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  • American Chemical Society  (106,103)
  • American Geophysical Union  (17,034)
  • 2010-2014  (94,823)
  • 1995-1999  (28,314)
  • 1985-1989
  • 2011  (45,866)
  • 2010  (48,957)
  • 1999  (28,314)
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  • 2010-2014  (94,823)
  • 1995-1999  (28,314)
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  • 1
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    Evolution of temperature, O3, CO, and N2O profiles during the exceptional 2009 Arctic major stratospheric warming as observed by lidar and mm-wave spectroscopy at Thule (76.5°N, 68.8°W), Greenland. (2010)
    American Geophysical Union
    Details
    Publication Date: 2020-12-18
    Description: The 2009 Arctic sudden stratospheric warming (SSW) was the most intense event of this kind ever observed. Unique ground-based measurements of middle atmospheric profiles for temperature, O3, CO, and N2O obtained at Thule (76.5°N, 68.8°W), Greenland, in the period January – early March are used to show the evolution of the 2009 SSW in the region of its maximum intensity. The first sign of the SSW was detected at θ~2000 K on January 19, when a rapid decrease in CO mixing ratio took place. The first evidence of a temperature increase was observed at the same level on 22 January, the earliest date on which lidar measurements reached above ~50 km. The warming propagated from the upper to the lower stratosphere in 7 days and the record maximum temperature of 289 K was observed between 1300 and 1500 K potential temperature on 22 January. A strong vortex splitting was associated with the SSW. Stratospheric backward trajectories indicate that airmasses arriving to Thule during the warming peak underwent a rapid compression and an intense adiabatic warming of up to 50 K. The rapid advection of air from the extra-tropics was also occasionally observed to produce elevated values of N2O mixing ratio. Starting from mid-February the temperature profile and the N2O mixing ratio returned to the pre-warming values in the mid and upper stratosphere, indicating the reformation of the vortex at these levels. In late winter, vertical descent from starting altitudes of ~60 km is estimated from CO profiles to be 0.25±0.05 km/day.
    Description: Published
    Description: D24315
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 1.10. TTC - Telerilevamento
    Description: JCR Journal
    Description: open
    Keywords: sudden stratospheric warming ; winter polar stratosphere ; temperature ; O3 ; N2O ; CO ; 01. Atmosphere::01.01. Atmosphere::01.01.01. Composition and Structure ; 01. Atmosphere::01.01. Atmosphere::01.01.04. Processes and Dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    An unloading foam model to constrain Etna’s 11–13 January 2011 lava fountaining episode (2011)
    American Geophysical Union
    Details
    Publication Date: 2021-06-09
    Description: The 11–13 January 2011 eruptive episode at Etna volcano occurred after several months of increasing ash emissions from the summit craters, and was heralded by increasing SO2 output, which peaked at ∼5000 megagrams/day several hours before the start of the eruptive activity. The eruptive episode began with a phase of Strombolian activity from a pit crater on the eastern flank of the SE‐Crater. Explosions became more intense with time and eventually became transitional between Strombolian and fountaining, before moving into a lava fountaining phase. Fountaining was accompanied by lava output from the lower rim of the pit crater. Emplacement of the resulting lava flow field, as well as associated lava fountain‐ and Strombolian‐phases, was tracked using a remote sensing network comprising both thermal and visible cameras. Thermal surveys completed once the eruptive episode had ended also allowed us to reconstruct the emplacement of the lava flow field. Using a high temporal resolution geostationary satellite data we were also able to construct a detailed record of the heat flux during the fountain‐fed flow phase and its subsequent cooling. The dense rock volume of erupted lava obtained from the satellite data was 1.2 × 106 m3; this was emplaced over a period of about 6 h to give a mean output rate of ∼55 m3 s−1. By comparison, geologic data allowed us to estimate dense rock volumes of ∼0.85 × 106 m3 for the pyroclastics erupted during the lava fountain phase, and 0.84–1.7 × 106 m3 for lavas erupted during the effusive phase, resulting in a total erupted dense rock volume of 1.7–2.5 × 106 m3 and a mean output rate of 78–117 m3 s−1. The sequence of events and quantitative results presented here shed light on the shallow feeding system of the volcano.
    Description: Published
    Description: B11207
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: partially_open
    Keywords: Etna ; lava fountains ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 3
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    Turbulent times in the northern polar ionosphere? (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-12-03
    Description: A model is presented of the growth rate of turbulently generated irregularities in the electron concentration of northern polar cap plasma patches. The turbulence is generated by the short‐term fluctuations in the electric field imposed on the polar cap ionosphere by electric field mapping from the magnetosphere. The model uses an ionospheric imaging algorithm to specify the state of the ionosphere throughout. The growth rates are used to estimate mean amplitudes for the irregularities, and these mean amplitudes are compared with observations of the scintillation indices S4 and s by calculating the linear correlation coefficients between them. The scintillation data are recorded by GPS L1 band receivers stationed at high northern latitudes. A total of 13 days are analyzed, covering four separate magnetic storm periods. These results are compared with those from a similar model of the gradient drift instability (GDI) growth rate. Overall, the results show better correlation between the GDI process and the scintillation indices than for the turbulence process and the scintillation indices. Two storms, however, show approximately equally good correlations for both processes, indicating that there might be times when the turbulence process of irregularity formation on plasma patches may be the controlling one.
    Description: Published
    Description: A04310
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: ionospheric irregularities ; scintillations ; Gradient Drift Instability ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.07. Scintillations ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 4
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    Shallow subduction beneath Italy: Three-dimensional images of the Adriatic-European-Tyrrhenian lithosphere system based on high-quality P wave arrival times (2010)
    American Geophysical Union
    Details
    Publication Date: 2020-10-26
    Description: This paper presents a velocity model of the Italian (central Mediterranean) lithosphere in unprecedented detail. The model is derived by inverting a set of 166,000 Pg and Pn seismic wave arrival times, restricted to the highest-quality data available. The tomographic images reveal the geometry of the subduction-collision system between the European, Adriatic, and Tyrrhenian plates, over a larger volume and with finer resolution than previous studies. We find two arcs of low-Vp anomalies running along the Alps and the Apennines, describing the collision zones of underthrusting continental lithospheres. Our results suggest that in the Apennines, a significant portion of the crust has been subducted below the mountain belt. From the velocity model we can also infer thermal softening of the crustal wedge above the subducting Adriatic plate. In the Tyrrhenian back-arc region, strong and extensive low-Vp anomalies depict upwelling asthenospheric material. The tomographic images also allow us to trace the boundary between the Adriatic and the Tyrrhenian plates at Moho depth, revealing some tears in the Adriatic-Ionian subducting lithosphere. The complex lithospheric structure described by this study is the result of a long evolution; the heterogeneities of continental margins, lithospheric underthrusting, and plate indentation have led to subduction variations, slab tears, and asthenospheric upwelling at the present day. The high-resolution model provided here greatly improves our understanding of the central Mediterranean’s structural puzzle. The results of this study can also shed light on the evolution of other regions experiencing both oceanic and continental subduction.
    Description: Published
    Description: B05305
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: lithosphere ; crust ; italy ; plates ; subduction ; europe ; seismicity ; adria ; tyrrhenian ; boundary ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 5
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    High resolution velocity structure beneath Mount Vesuvius from seismic array data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: A high resolution P-wave image of Mt. Vesuvius edifice has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes, land based shots and small aperture array data. The results give detailsdownto300 – 500m.Therelocatedlocalseismicity appears to extend down to 5 km below the central crater, distributed in a major cluster, centered at 3 km below the central crater and in a minor group, with diffuse hypocenters inside the volcanic edifice. The two clusters are separated by an anomalously high Vp region at around 1 km depth. A zone with high Vp/Vs in the upper layers is interpreted as produced by the presence of intense fluid circulation. The highest energy quakes (up to M = 3.6) are located in the deeper cluster, in a high P-wave velocity zone. Our results favor an interpretation in terms of absence of shallow magma reservoirs.
    Description: Published
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Velocity Tomography ; Mt. Vesuvius ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 6
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    Topography of the Calabria subduction zone (southern Italy): Clues for the origin of Mt. Etna (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Calabria represents an ideal site to analyze the topography of a subduction zone as it is located on top of a narrow active Wadati-Benioff zone and shows evidence of rapid uplift. We analyzed a pattern of surface deformation using elevation data with different filters and showed the existence of a long wavelength (〉100 km) relatively positive topographic signal at the slab edges. The elevation of MIS 5.5 stage marine terraces supports this pattern, although the record is incomplete and partly masked by the variable denudation rate. We performed structural analyses along the major active or recently reactivated normal faults showing that the extensional direction varies along the Calabrian Arc and laterally switches from arc-normal, within the active portion of the slab, to arc-oblique or even arc-parallel, along the northern and southern slab edges. This surface deformation pattern was compared with a recent high resolution P wave tomographic model showing that the high seismic velocity anomaly is continuous only within the active Wadati-Benioff zone, whereas the northern and southwestern sides are marked by low velocity anomalies, suggesting that large-scale topographic bulges, volcanism, and uplift could have been produced by mantle upwelling. We present numerical simulations to visualize the three-dimensional mantle circulation around a narrow retreating slab, ideally similar to the one presently subducting beneath Calabria. We emphasize that mantle upwelling and surface deformation are expected at the edges of the slab, where return flows may eventually drive decompression melting and the Mount Etna volcanism.
    Description: Published
    Description: TC1003
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: topography ; Calabrian Arc ; subduction ; tomography ; mantle flow ; uplift ; retreat ; anisotropy ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 7
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    The 16 November 2006 flank collapse of the south-east crater at Mount Etna, Italy: Study of the deposit and hazard assessment (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On 16 November 2006 a flank collapse affected the unstable eastern slope of the South-East Crater (SEC) of Mount Etna. The collapse occurred during one of the paroxysmal events with sustained strombolian activity that characterized the August–December 2006 eruption and was triggered by erosion of loose, hydrothermally altered material of the steep south-east sector of SEC from the outpour of lava. The collapse produced a debris avalanche that involved both lithic and juvenile material and resulted in a deposit emplaced on the eastern flank of the volcano up to 1.2 km away from the source. The total volume of the deposit was estimated to be in the order of 330,000–413,000 m3. The reconstruction of the collapse event was simulated using TITAN2D software designed to model granular avalanches and landslides. This approach can be used to estimate areas that may be affected by similar collapse events in the future. The area affected by the 16 November 2006 lateral collapse of SEC was a small portion of the Mount Etna summit area, but the fact that no one was killed or injured should be considered fortuitous. The summit and adjacent areas of the volcano, in fact, are usually visited by many tourists who are not prepared to face this type of danger. The 16 November 2006 collapse points to the need to be prepared for similar events through scientific investigation (analysis of flank instability, numerical simulation of flows) and development of specific civil protection plans.
    Description: Published
    Description: B02204
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: Mount Etna ; flank instability ; volcaniclastic deposit ; granular flows ; numerical simulation ; volcanic hazard ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 8
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    Seismic and landslide source of the 1908 Straits of Messina tsunami (Sicily, Italy) (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One hundred years ago (December 1908) a devastating tsunami associated with an earthquake struck the Straits of Messina area, causing many casualties. On the basis of seismic data and observed runups and arrival times, we suggest that the tsunami was likely generated by coseismic seafloor displacement coupled with a small submarine landslide triggered by the earthquake. Backwards ray-tracing using a depth-dependent velocity field, submarine slope analysis and inferences form the main drainage network allowed us to identify possible locations for the source of the submarine landslide. We then performed direct simulations of tsunamis generated by the earthquake and landslides and identified the tsunami source (earthquake plus landslide) that best fits observational data in a small volume submarine landslide (1–5 km3) located offshore Nizza, Sicily.
    Description: Published
    Description: L16304
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale
    Description: 4.6. Oceanografia operativa per la valutazione dei rischi in aree marine
    Description: JCR Journal
    Description: reserved
    Keywords: earthquake ; landslide ; tsunami ; 03. Hydrosphere::03.01. General::03.01.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 9
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    Kinematics and Source Zone Properties of the 2004 Sumatra-Andaman Earthquake and Tsunami: Nonlinear Joint Inversion of Tide-Gage, Satellite Altimetry and GPS data (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We (re)analyzed the source of the 26 December 2004 Sumatra-Andaman earthquake and tsunami through a nonlinear joint inversion of an in-homogeneous dataset made up of tide-gages, satellite altimetry, and far-field GPS recordings. The purpose is two-fold: (1) the retrieval of the main kinematics rupture parameters (slip, rake, rupture velocity); (2) the inference of the rigidity of the source zone. We independently estimate the slip from tsunami data and the seismic moment from geodetic data, so to derive the rigidity. Our results confirm that the source of the 2004 Sumatra-Andaman earthquake has a complex geometry, constituted by three main slip patches, with slip peaking at ~30 meters in the Southern part of the source. The rake direction rotates counter-clockwise at North, according to the direction of convergence along the trench. The rupture velocity is higher in the deeper than in the shallower part of the source, consistently with the expected increase of rigidity with depth. It is also lower in the Northern part, consistently with known variations of the incoming plate properties and shear velocity. Our model features a rigidity (20-30 GPa), that is lower than PREM average for the seismogenic volume [Dziewonski and Anderson, 1981]. The source rigidity is one of the factors controlling the tsunamigenesis: for a given seismic moment, the lower the rigidity, the higher the induced seafloor displacement. The general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation.
    Description: In press
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: Source process ; Sumatra ; Tsunami ; joint inversion ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 10
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    Laboratory measurements of the frictional properties of the Zuccale 3 low-angle normal fault, Elba Island, Italy (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Using a case study from the island of Elba, Italy, we seek to test the hypothesis that 7 the presence of minerals with low frictional strengths can explain prolonged slip on 8 low-angle normal faults. The central core of the Zuccale low-angle normal fault 9 contains a distinctive fault rock zonation that developed during progressive exhumation. 10 Most fault rock components preserve microstructural evidence for having accommodated 11 deformation entirely, or partly, by frictional mechanisms. One millimeter thick sample 12 powders of all the major fault rock components were deformed in a triaxial deformation 13 apparatus under water-saturated conditions, at room temperature, and at constant effective 14 normal stresses of 25, 50, and 75 MPa. Pore fluid pressure was maintained at 50 MPa 15 throughout. Overall, the coefficient of friction (m) of the fault rocks varies between 16 0.25 and 0.8, emphasizing the marked strength heterogeneity that may exist within 17 natural fault zones. Also, m is strongly dependent on fault rock mineralogy and is 18 〈0.45 for fault rocks containing talc, chlorite, and kaolinite and 〉0.6 for fault rocks 19 dominated by quartz, dolomite, calcite, and amphibole. Localization of frictional slip 20 within talc-rich portions of the fault core can potentially explain movements along the 21 Zuccale fault over a wide range of depths within the upper crust, although the 22 mechanical importance of the talc-bearing fault rocks likely decreased following their 23 dismemberment into a series of poorly connected fault rock lenses. Additionally, slip 24 within clay-bearing fault gouges with m between 0.4 and 0.5 may have facilitated 25 movements in the uppermost (〈2 km) crust. For several other fault rock components, 26 m varies between 0.5 and 0.8, and mineralogical weakening alone is insufficient to 27 account for low-angle slip. In the latter fault rock components, other weakening 28 mechanisms such as the development of high fluid pressures, or dissolution-precipitation 29 creep, may have been particularly important in reducing fault strength.
    Description: In press
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: Friction ; Low-Angle Normal Faults ; Experiments ; Weakening ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
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  • 11
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    On the transient behavior of frictional melt during seismic slip (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In a recent work on the problem of sliding surfaces under the presence of frictional melt (applying in particular to earthquake fault dynamics), we derived from first principles an expression for the steady state friction compatible with experimental observations. Building on the expressions of heat and mass balance obtained in the above study for this particular case of Stefan problem (phase transition with a migrating boundary) we propose here an extension providing the full time-dependent solution (including the weakening transient after pervasive melting has started, the effect of eventual steps in velocity and the final decelerating phase). A system of coupled equations is derived and solved numerically. The resulting transient friction and wear evolution yield a satisfactory fit (1) with experiments performed under variable sliding velocities (0.9-2 m/s) and different normal stresses (0.5-20 MPa) for various rock types and (2) with estimates of slip weakening obtained from observations on ancient seismogenic faults that host pseudotachylite (solidified melt). The model allows to extrapolate the experimentally observed frictional behavior to large normal stresses representative of the seismogenic Earth crust (up to 200 MPa), high slip rates (up to 9 m/s) and cases where melt extrusion is negligible. Though weakening distance and peak stress vary widely, the net breakdown energy appears to be essentially independent of either slip velocity and normal stress. In addition, the response to earthquake-like slip can be simulated, showing a rapid friction recovery when slip rate drops. We discuss the properties of energy dissipation, transient duration, velocity weakening, restrengthening in the decelerating final slip phase and the implications for earthquake source dynamics.
    Description: S.N. and G.D.T. were supported by a European Research Council Starting Grant Project (acronym USEMS) and by a Progetti di Eccellenza Fondazione Cassa di Risparmio di Padova e Rovigo. We are grateful to Nick Beeler (and to an anonymous referee) for their constructive reviews and their help to improve the clarity of the manuscript.
    Description: Published
    Description: B10301
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: Friction ; Melt ; Earthquake dynamics ; fault mechanics ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 12
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    Energy radiation from intermediate to large magnitude earthquakes: implications for dynamic fault weakening (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The amount of energy radiated from an earthquake can be measured using recent methods based on earthquake coda signals and spectral ratios. Such methods are not altered by either site or directivity effects, with the advantage of a greatly improved accuracy. Several studies of earthquake sequences based on the above measurements showed evidence of a breakdown in self-similarity in the moment to energy relation. Radiated energy can be also used as a gauge to estimate the average dynamic stress drop on the fault. Here we compute the dynamic stress drop, infer the co-seismic friction and estimate the co-seismic heating resulting from the frictional work during events from different main shock-aftershock earthquake sequences. We relate the dynamic friction to the maximum temperature rise estimated on the faults for each earthquake. Our results are strongly indicative that a thermally triggered dynamic frictional weakening is present, responsible for the breakdown in self-similarity. These observations from seismic data are compatible with recent laboratory evidence of thermal weakening in rock friction under seismic slip-rates, associated to various physical processes such as melting, decarbonation or dehydration.
    Description: Kevin Mayeda was supported under Weston Geophysical subcontract No. GC19762NGD and AFRL contract No. FA8718-06-C-0024. Work by L. Malagnini was performed under the auspices of the Dipartimento della Protezione Civile, under contract S3 – INGV-DPC (2007-2009), project: “Valutazione rapida dei parametri e degli effetti dei forti terremoti in Italia e nel Mediterraneo”.
    Description: Published
    Description: B06319
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: earthquake radiation ; coda ; friction ; self-similarity ; dynamic weakening ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 13
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    On claimed ULF seismogenic fractal signatures in the geomagnetic field (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: During the last ten years, fractal analysis of ultra-low-frequency (ULF) geomagnetic field components has been proposed as one of the most promising tools to highlight magnetic precursor signals possibly generated by the preparation processes of earthquakes. Several papers claim seismogenic changes in the fractal features of the geomagnetic field some months before earthquakes occur. The target of the present paper is to put forth a qualitative investigation on the fractal characteristics of ULF magnetic signatures that previous authors have claimed to be related without doubt to strong earthquakes. This analysis takes into account both the temporal evolution of the geomagnetic field fractal parameters reported in previous researches and the temporal evolution of global geomagnetic activity. Running averages of the geomagnetic indices ΣKp and Ap are plotted into the original figures from the previous publications. This simple analysis shows that the fractal features of the ULF geomagnetic field are closely related to the geomagnetic activity both before and after the earthquake occurs. The correlation between the geomagnetic field fractal parameters and geomagnetic activity is clearly shown over both long and short time scales. In light of this, the present paper shows that fractal behaviors of previously claimed seismogenic ULF magnetic signatures depend mainly on geomagnetic activity due to solar-terrestrial interaction. Therefore, previously reported association with the preparation process of the earthquake is dubious.
    Description: Published
    Description: A10236
    Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake precursors ; Geomagnetic field ; ULF ; Fractal analysis ; SOC ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.08. Instruments and techniques
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  • 14
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    Water vapor sounding with the far infrared REFIR-PAD spectroradiometer from a high-altitude ground-based station during the ECOWAR campaign (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: The Radiation Explorer in the Far InfraRed-Prototype for Applications and Development (REFIR-PAD) spectroradiometer was operated from the Testa Grigia Italian-Alps station in March 2007 during the Earth Cooling by Water Vapour Radiation (ECOWAR) measurement campaign, obtaining downwelling radiance spectra in the 100–1100 cm−1 range, under clear-sky conditions and in the presence of cirrus clouds. The analysis of these measurements has proven that the instrument is capable of determining precipitable water vapor with a total uncertainty of 5–7% by using the far-infrared rotational band of water. The measurement is unaffected by the presence of cirri, whose optical depth can be instead retrieved as an additional parameter. Information on the vertical profiles of water vapor volume mixing ratio and temperature can also be retrieved for three altitude levels. The ability to measure the water vapor column with a simple, uncooled instrument, capable of operating continuously and with a time resolution of about 10 min, makes REFIR-PAD a very valuable instrument for meteorological and climatological studies for the characterization of the water vapor distribution.
    Description: Published
    Description: D02310
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 1.10. TTC - Telerilevamento
    Description: JCR Journal
    Description: reserved
    Keywords: tropospheric water vapor ; IR spectroscopy ; REFIR-PAD ; ECOWAR ; 01. Atmosphere::01.01. Atmosphere::01.01.01. Composition and Structure ; 01. Atmosphere::01.01. Atmosphere::01.01.08. Instruments and techniques
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  • 15
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    Evolution of an active lava flow field using a multitemporal LIDAR acquisition (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Application of light detection and ranging (LIDAR) technology in volcanology has 7 developed rapidly over the past few years, being extremely useful for the generation 8 of high‐spatial‐resolution digital elevation models and for mapping eruption products. 9 However, LIDAR can also be used to yield detailed information about the dynamics of 10 lava movement, emplacement processes occuring across an active lava flow field, and the 11 volumes involved. Here we present the results of a multitemporal airborne LIDAR survey 12 flown to acquire data for an active flow field separated by time intervals ranging from 13 15 min to 25 h. Overflights were carried out over 2 d during the 2006 eruption of Mt. Etna, 14 Italy, coincident with lava emission from three ephemeral vent zones to feed lava flow in 15 six channels. In total 53 LIDAR images were collected, allowing us to track the volumetric 16 evolution of the entire flow field with temporal resolutions as low as ∼15 min and at a 17 spatial resolution of 〈1 m. This, together with accurate correction for systematic errors, 18 finely tuned DEM‐to‐DEM coregistration and an accurate residual error assessment, 19 permitted the quantification of the volumetric changes occuring across the flow field. We 20 record a characteristic flow emplacement mode, whereby flow front advance and channel 21 construction is fed by a series of volume pulses from the master vent. Volume pulses 22 have a characteristic morphology represented by a wave that moves down the channel 23 modifying existing channel‐levee constructs across the proximal‐medial zone and building 24 new ones in the distal zone. Our high‐resolution multitemporal LIDAR‐derived DEMs 25 allow calculation of the time‐averaged discharge rates associated with such a pulsed flow 26 emplacement regime, with errors under 1% for daily averaged values.
    Description: This work was partially funded by the Italian 930 Dipartimento della Protezione Civile in the frame of the 2007–2009 Agree- 931 ment with Istituto Nazionale di Geofisica e Vulcanologia–INGV. A.F. 932 benefited from the MIUR‐FIRB project “Piattaforma di ricerca multi‐disci- 933 plinare su terremoti e vulcani (AIRPLANE)” n. RBPR05B2ZJ. S.T. 934 benefited from the project FIRB “Sviluppo di nuove tecnologie per la prote- 935 zione e difesa del territorio dai rischi naturali (FUMO)” funded by the Italian 936 Ministero dell’Istruzione, dell’Università e della Ricerca.
    Description: Published
    Description: B11203
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 1.10. TTC - Telerilevamento
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: LIDAR ; lava flow ; Etna ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
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  • 16
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    A completeness analysis of the national seismic network of Italy (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Accepted for publication in Journal of Geophysical Research. Copyright (2009) American Geophysical Union. Further reproduction or electronic distribution is not permitted.
    Description: We present the first detailed study of earthquake detection capabilities of the Italian National Seismic Network and of the completeness threshold of its earthquake catalog. The network in its present form started operating on 16 April 2005 and is a significant improvement over the previous networks. For our analysis, we employed the PMC method as introduced by Schorlemmer and Woessner (2008). This method does not estimate completeness from earthquakes samples as traditional methods, mostly based on the linearity of earthquake-size distributions. It derives detection capabilities for each station of the network and synthesizes them into maps of detection probabilities for earthquakes of a given magnitude. Thus, this method avoids the many assumptions about earthquake distributions that traditional methods make. The results show that the Italian National Seismic Network is complete at $M=2.9$ for the entire territory excluding the islands of Sardinia, Pantelleria, and Lampedusa. At the $M=2.5$ level, which is the reporting threshold level of the Italian Civil Protection, the network may miss events in southern parts of Apulia and the western part of Sicily. The stations are connected through many different telemetry links to the operational datacenter in Rome. Scenario computations show that no significant drop in completeness occurs if one of the three major links fail, indicating a well-balanced network setup.
    Description: In press
    Description: 1.1. TTC - Monitoraggio sismico del territorio nazionale
    Description: JCR Journal
    Description: open
    Keywords: Italian seismicity ; earthquake detection capability ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
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  • 17
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    Real-time forecasting following a damaging earthquake (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An edited version of this paper was published by AGU. Copyright (2009) American Geophysical Union.
    Description: We describe the results of a prospective, real-time earthquake forecast experiment made during a seismic emergency. A $M_w$ 6.3 earthquake struck the city of L'Aquila, Italy on April 6, 2009, causing hundreds of deaths and vast damage. Immediately following this event, we began producing daily earthquake forecasts for the region, and we provided these forecasts to Civil Protection -- the agency responsible for managing the emergency. The forecasts are based on a stochastic model that combines the Gutenberg-Richter distribution of earthquake magnitudes and power-law decay in space and time of triggered earthquakes. The results from the first month following the L'Aquila earthquake exhibit a good fit between forecasts and observations, indicating that accurate earthquake forecasting is now a realistic goal. Our experience with this experiment demonstrates an urgent need for a connection between probabilistic forecasts and decision-making in order to establish -- before crises -- quantitative and transparent protocols for decision support.
    Description: Published
    Description: L21302
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: partially_open
    Keywords: earthquake forecast ; L'Aquila earthquake ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
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  • 18
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    Topographic control on lava flow paths at Mount Etna, Italy: Implications for hazard assessment (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Assessment of the hazard from lava flow inundation at the active volcano of Mount Etna, Italy, was performed by calculating the probability of lava flow inundation at each position on the volcano. A probability distribution for the formation of new vents was calculated using geological and volcanological data from past eruptions. The simulated lava flows from these vents were emplaced using a maximum expected flow length derived from geological data on previous lava flows. Simulations were run using DOWNFLOW, a digital-elevation-model-based model designed to predict lava flow paths. Different eruptive scenarios were simulated by varying the elevation and probability distribution of eruptive points. Inundation maps show that the city of Catania and the coastal zone may only be impacted by flows erupted from low-altitude vents (〈1500 m elevation) and that flank eruptions at elevations 〉2000 m preferentially inundate the northeast and southern sectors of the volcano as well as the Valle del Bove. Eruptions occurring in the summit area (〉3000 m elevation) pose no threat to the local population. Discrepancies between the results of simple, hydrological models and those of the DOWNFLOW model show that hydrological approaches are inappropriate when dealing with Etnean lava flows. Because hydrological approaches are not designed to reproduce the full complexity of lava flow spreading, they underestimate the catchment basins when the fluid has a complex rheology.
    Description: Published
    Description: F01019
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: volcanic hazard ; lava flow ; Mount Etna ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 19
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    Predicting the impact of lava flows at Mount Etna, Italy (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Forecasting the time, nature, and impact of future eruptions is difficult at volcanoes such as Mount Etna, in Italy, where eruptions occur from the summit and on the flanks, affecting areas distant from each other. Nonetheless, the identification and quantification of areas at risk from new eruptions are fundamental for mitigating potential human casualties and material damage. Here, we present new results from the application of a methodology to define flexible high‐resolution lava invasion susceptibility maps based on a reliable computational model for simulating lava flows at Etna and on a validation procedure for assessing the correctness of susceptibility mapping in the study area. Furthermore, specific scenarios can be extracted at any time from the simulation database, for land use and civil defense planning in the long term, to quantify, in real time, the impact of an imminent eruption, and to assess the efficiency of protective measures.
    Description: This work was sponsored by the Italian Ministry for Education, University and Research, FIRB project RBAU01RMZ4 “Lava flow simulations by Cellular Automata,” and by the National Civil Defense Department and INGV (National Institute of Geophysics and Volcanology), project V3_6/09 “V3_6 – Etna.”
    Description: Published
    Description: B04203
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 4.4. Scenari e mitigazione del rischio ambientale
    Description: JCR Journal
    Description: reserved
    Keywords: lava flows ; volcanic hazard ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.03. Geomorphology ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.01. Computational geophysics::05.01.02. Cellular automata, fuzzy logic, genetic alghoritms, neural networks ; 05. General::05.01. Computational geophysics::05.01.05. Algorithms and implementation ; 05. General::05.02. Data dissemination::05.02.99. General or miscellaneous ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions ; 05. General::05.08. Risk::05.08.99. General or miscellaneous ; 05. General::05.09. Miscellaneous::05.09.99. General or miscellaneous
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  • 20
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    Slip Distribution of the 2003 Tokachi-oki Mw 8.1 earthquake from joint inversion of tsunami waveforms and geodetic data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: We study the 2003 Mw 8.1 Tokachi‐oki earthquake, a great interplate event that occurred along the southwestern Kuril Trench and generated a significant tsunami. To determine the earthquake slip distribution, we perform the first joint inversion of tsunami waveforms measured by tide gauges and of coseismic displacement measured both by GPS stations and three ocean bottom pressure gauges (PG) for this event. The resolution of the different data sets on the slip distribution is assessed by means of several checkerboard tests. Results show that tsunami data constrain the slip distribution offshore, whereas GPS data constrain the slip distribution in the onshore zone. The three PG data only coarsely constrain the offshore slip, indicating that denser networks should be installed close to subduction zones. Combining the three data sets significantly improves the inversion results. Joint inversion of the 2003 Tokachi‐oki earthquake data leads to maximum slip values (∼6 m) confined at depths greater than ∼25 km, between 30 and 80 km northwest of the hypocenter, with a patch of slip (3 m) in the deepest part of the source (∼50 km depth). Slip values are very low (≤1 m) updip from the hypocenter. Furthermore, the rupture does not extend on the plate interface off Akkeshi. As a significant back slip amount (∼4 m) has accumulated there since the last 1952 earthquake, this segment could rupture during the next large interplate event along the Kuril Trench.
    Description: Published
    Description: B11313
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: tsunami ; coseismic displacement ; joint inversion ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 21
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    A relation between lava discharge rate, thermal insulation, and flow area set using lidar data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: A simple linear relation can be used to link time averaged discharge rate (TADR) and lava flow area (A). The relation applies to given insulation conditions, as described by the characteristic flow surface temperature (Te), and will vary from case-to-case depending on rheological and topographic influences on flow spreading. Most flows have insulation conditions that change through time, modifying the relationship between TADR and area as insulation conditions evolve. Using lidar data we can define TADR, the flow area that the discharge feeds and Te, allowing generation of a case-specific relation to convert satellite-data-derived flow areas to TADR. For Etna's 2006 lava flow field we obtain a relation whereby TADR = 5.6 × 10−6 A for well insulated conditions (Te = 100°C) and TADR = 1.5 × 10−4 A for poorly insulated conditions (Te = 600°C).
    Description: Published
    Description: L20308
    Description: 1.10. TTC - Telerilevamento
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: lava flow ; discharge rate ; area ; surface temperature ; lidar ; Etna. ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 22
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    Magnetic properties of sedimentary greigite (Fe3S4): an update (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Greigite (Fe3S4) is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction. It can also grow at any time when dissolved iron and sulfide are available during diagenesis. Greigite is important in paleomagnetic, environmental, biological, biogeochemical, tectonic, and industrial processes. Much recent progress has been made in understanding its magnetic properties. Greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites. The crystallographic c axis is the easy axis of magnetization, with magnetic properties dominated by magnetocrystalline anisotropy. Robust empirical estimates of the saturation magnetization, anisotropy constant, and exchange constant for greigite have been obtained recently for the first time, and the first robust estimate of the low‐field magnetic susceptibility is reported here. The Curie temperature of greigite remains unknown but must exceed 350°C. Greigite lacks a low‐temperature magnetic transition. On the basis of preliminary micromagnetic modeling, the size range for stable single domain behavior is 17–200 nm for cubic crystals and 17–500 nm for octahedral crystals. Gradual variation in magnetic properties is observed through the pseudo‐single‐domain size range. We systematically document the known magnetic properties of greigite (at high, ambient, and low temperatures and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties. Recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite, which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records, including widespread remagnetizations.
    Description: Published
    Description: RG1002
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: greigite ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
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  • 23
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    Principles of volcanic risk metrics: theory and the case study of Mt. Vesuvius and Campi Flegrei (Italy) (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An edited version of this paper was published by AGU. Copyright (2009) American Geophysical Union.
    Description: Despite volcanic risk having been defined quantitatively more than 30 years ago, this risk has been managed without being effectively measured. The recent substantial progress in quantifying eruption probability paves the way for a new era of rational science-based volcano risk management, based on what may be termed ‘‘volcanic risk metrics’’ (VRM). In this paper, we propose the basic principles of VRM, based on coupling probabilistic volcanic hazard assessment and eruption forecasting with cost-benefit analysis. The VRM strategy has the potential to rationalize decision making across a broad spectrum of volcanological questions. When should the call for evacuation be made? What early preparations should be made for a volcano crisis? Is it worthwhile waiting longer? What areas should be covered by an emergency plan? During unrest, what areas of a large volcanic field or caldera should be evacuated, and when? The VRM strategy has the paramount advantage of providing a set of quantitative and transparent rules that can be established well in advance of a crisis, optimizing and clarifying decision-making procedures. It enables volcanologists to apply all their scientific knowledge and observational information to assist authorities in quantifying the positive and negative risk implications of any decision.
    Description: Published
    Description: B03213
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: risk assessment ; decision making ; campi flegrei ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 24
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    Vesiculation in magmas from Stromboli and implications for normal Strombolian activity and paroxysmal explosions in basaltic systems (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We performed a series of X-ray tomographic experiments and lattice Boltzmann permeability simulations on pyroclastic products from explosive activity at Stromboli between December 2004 and May 2006. We reconstructed the 3-D textures of vesicles to investigate the relationship between the nature of vesiculation in the erupted products and the dynamics of gas transport in the shallow conduit in order to derive implications for the eruptive behavior of basaltic volcanoes. Scoriae from normal Strombolian explosions display remarkably consistent vesicle volume distributions fit by power laws with an exponent of 1 (±0.2). We ascribe the origin of such distributions to the combined effect of coalescence and continuous nucleation events in the steady state, shallow magma system that supplies normal Strombolian activity. Volume distributions and textures of vesicles in pumice clasts from the 5 April 2003 and 15 March 2007 paroxysmal activity are markedly different from those in the scoriae. Besides a power law function with a higher exponent, portions of these distributions can be also fit by an exponential function, suggesting the attempt of the system to reach near-equilibrium conditions. The investigated pumice clasts also lack the large, connecting vesicles responsible for the development of degassing pathways in the Stromboli magma that erupts the scoriae. This testifies to a decreased degassing efficiency of the magma associated with paroxysmal explosions and potential overpressure buildup at depth. By comparison with degassing experiments on basaltic melts, we derive a time constraint on the order of minutes to hours for the incubation of paroxysms at Stromboli.
    Description: Published
    Description: B01206
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: basaltic explosions ; vesicle textures ; third dimension ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
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  • 25
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    Long term variations of the Campi Flegrei (Italy) volcanic system as revealed by the monitoring of hydrothermal activity (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Long duration time-series of the chemical composition of fumaroles and of soil CO2 flux reveal that important variations in the activity of the Solfatara fumarolic field, the most important hydrothermal site of Campi Flegrei, occurred in the 2000-2008 period. A continuous increase of the CO2 concentrations, and a general decrease of the CH4 concentrations are interpreted as the consequence of the increment of the relative amount of magmatic fluids, rich in CO2 and poor in CH4, hosted by the hydrothermal system. Contemporaneously, the H2O-CO2-He-N2 gas system shows remarkable compositional variations in the samples collected after July 2000 with respect to the previous ones, indicating the progressive arrival at the surface of a magmatic component different from that involved in the 1983-84 episode of volcanic unrest (1983-1984 bradyseism). The change starts in 2000 concurrently with the occurrence of relatively deep, long-period seismic events which were the indicator of the opening of an easy-ascent pathway for the transfer of magmatic fluids towards the shallower, brittle domain hosting the hydrothermal system. Since 2000, this magmatic gas source is active and causes ground deformations, seismicity as well as the expansion of the area affected by soil degassing of deeply derived CO2. Even though the activity will most probably be limited to the expulsion of large amounts of gases and thermal energy, as observed in other volcanoes and in the past activity of Campi Flegrei, the behavior of the system in the future is, at the moment, unpredictable.
    Description: Published
    Description: B03205
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: 2.4. TTC - Laboratori di geochimica dei fluidi
    Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi
    Description: JCR Journal
    Description: reserved
    Keywords: Campi Flegrei ; CO2 ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 26
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    A new velocity field for Greece: Implications for the kinematics and dynamics of the Aegean (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: A new set of geodetic velocities for Greece and the Aegean, derived from 254 survey-mode and continuous GPS sites, is used to test kinematic and dynamic models for this area of rapid continental deformation. Modeling the kinematics of the Aegean by the rotation of a small number (3–6) of blocks produces RMS misfits of ~5 mm yr−1 in the southern Aegean and western Peloponnese, indicating significant internal strain within these postulated blocks. It is possible to fit the observed velocities to within 2–3 mm yr−1 (RMS) by models that contain 10 or more blocks, but many such models can be found, with widely varying arrangements of blocks, that fit the data equally well provided that the horizontal dimension of those blocks is not larger than 100–200 km. A continuous field of velocity calculated from the GPS velocities by assuming that strain rates are homogeneous on the scale of ~120 km fits the observed velocities to better than 2–3 mm yr−1 (RMS), with systematic misfits, representing more localized strain, confined to a region approximately 100 × 100 km in size around the western Gulf of Corinth. This velocity field accounts for the major active tectonic features of Greece and the Aegean, including the widespread north-south extensional deformation and the distributed strike-slip deformation in the NE Aegean and western Greece. The T axes of earthquakes are aligned with the principal axes of elongation in the geodetic field, major active normal fault systems are perpendicular to those axes, and ~90% of the large earthquakes in this region during the past 120 years took place within the areas in which the geodetic strain rate exceeds 30 nanostrain yr−1. These observations suggest that the faulting within the upper crust of the Aegean region is driven by forces that are coherent over a scale that is significantly greater than 100 km. It is likely that those forces arise primarily from differences in gravitational potential energy within the lithosphere of the region.
    Description: Published
    Description: B10403
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: GPS ; Greece ; 04. Solid Earth::04.03. Geodesy::04.03.99. General or miscellaneous
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  • 27
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    Patterns in the recent 2007–2008 activity of Mount Etna volcano investigated by integrated geophysical and geochemical observations (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union
    Description: Seismic, deformation, and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment. In spite of their wide use, there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques. Here we combine seismic (volcanic tremor and long‐period seismicity), deformation (GPS), and geochemical (volcanic gas plume CO2/SO2 ratios) measurements in an attempt to interpret trends in the recent (2007–2008) activity of Etna volcano. We show that each eruptive episode occurring at the Southeast Crater (SEC) was preceded by a cyclic phase of increase‐decrease of plume CO2/SO2 ratios and by inflation of the volcano’s summit captured by the GPS network. These observations are interpreted as reflecting the persistent supply of CO2‐rich gas bubbles (and eventually more primitive magmas) to a shallow (depth of 1–2.8 km asl) magma storage zone below the volcano’s central craters (CCs). Overpressuring of the resident magma stored in the upper CCs’ conduit triggers further magma ascent and finally eruption at SEC, a process which we capture as an abrupt increase in tremor amplitude, an upward (〉2800 m asl) and eastward migration of the source location of seismic tremor, and a rapid contraction of the volcano’s summit. Resumption of volcanic activity at SEC was also systematically anticipated by declining plume CO2/SO2 ratios, consistent with magma degassing being diverted from the central conduit area (toward SEC).
    Description: Published
    Description: Q09008
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: 1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: volcano monitoring ; Mt. Etna volcano ; geochemistry and geophysics ; volcanic tremor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
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  • 28
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    Response of Mount Etna to dynamic stresses from distant earthquakes (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Influences of distant earthquakes on volcanic systems by dynamic stress transfer are well documented. We analyzed seismic signals and volcanic activity at Mount Etna during two periods, January 2006 and May 2008, that clearly showed variations coincident with distant earthquakes. In the first period, characterized by mild volcano activity, the effect of the dynamic stress transfer, caused by an earthquake in Greece (M = 6.8), was twofold: (1) banded tremor activity changed its features and almost disappeared; (2) a swarm of volcano‐tectonic (VT) earthquakes took place. The changes of the banded tremor were likely due to variations in rock permeability, caused by fluid flows driven by dynamic strain. The VT earthquake swarm probably developed as a secondary process, promoted by the dynamically triggered activation of magmatic fluids. The second period, May 2008, showed an intense explosive activity. During this interval, the dynamic stress transfer, associated with the arrival of the seismic waves of the Sichuan earthquake (M = 7.9), affected the character of the seismo‐volcanic signals and on the following day triggered an eruption. In particular, we observed changes in volcanic tremor and increases of both occurrence rate and energy of long period events. In this case, we suggest that dynamic stress transfer caused nucleation of new bubbles in volatile‐rich magma bodies with consequent buildup of pressure, highlighted by the increase of long period activity, followed by the occurrence of an eruption. We conclude that stresses from distant earthquakes are capable of modifying the state of the volcano.
    Description: Published
    Description: B12304
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Mt. Etna volcano ; dynamic stress transfer ; triggered eruption ; triggered seismicity ; volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 29
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    Anatomy of an unstable volcano from InSAR: Multiple processes affecting flank instability at Mt. Etna, 1994–2008 (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Volcano deformation may occur under different conditions. To understand how a volcano deforms, as well as relations with magmatic activity, we studied Mt. Etna in detail using interferometric synthetic aperture radar (InSAR) data from 1994 to 2008. From 1994 to 2000, the volcano inflated with a linear behavior. The inflation was accompanied by eastward and westward slip on the eastern and western flanks, respectively. The portions proximal to the summit showed higher inflation rates, whereas the distal portions showed several sectors bounded by faults, in some cases behaving as rigid blocks. From 2000 to 2003, the deformation became nonlinear, especially on the proximal eastern and western flanks, showing marked eastward and westward displacements, respectively. This behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002–2003 eruptions. From 2003 to 2008, the deformation approached linearity again, even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002. The eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those (largely inactive) to the south. In addition, from 1994 to 2008 part of the volcano base (south, west, and north lower slopes) experienced a consistent trend of uplift on the order of ∼0.5 cm/yr. This study reveals that the flanks of Etna have undergone a complex instability resulting from three main processes. In the long term (103–104 years), the load of the volcano is responsible for the development of a peripheral bulge. In the intermediate term (≤101 years, observed from 1994 to 2000), inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks. In the short term (≤1 year, observed from 2001 to 2002), the emplacement of feeder dikes along the NE and south rifts results in a nonlinear, focused, and asymmetric deformation on the eastern and western flanks. Deformation due to flank instability is widespread at Mt. Etna, regardless of volcanic activity, and remains by far the predominant type of deformation on the volcano.
    Description: ESA provided the SAR data (Cat‐1 no. 4532 and GEO Supersite initiative). The DEM was obtained from the SRTM archive, while the ERS‐1/2 orbits are courtesy of the TU‐Delft, The Netherlands. This work was partially funded by INGV and the Italian DPC (DPCINGV project V4 “Flank”), the Italian DPC (under special agreement with IREA‐CNR), and the Italian Space Agency under contract “sistema rischio vulcanico (SRV).” The authors thank Francesco Casu, Paolo Berardino, and Riccardo Lanari for their support and Geoff Wadge and Michael Poland for their helpful and constructive review of the manuscript.
    Description: Published
    Description: B10405
    Description: 1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 1.10. TTC - Telerilevamento
    Description: 3.2. Tettonica attiva
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: Flank instability ; InSAR ; volcanoes ; Etna ; 04. Solid Earth::04.01. Earth Interior::04.01.99. General or miscellaneous ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.02. Exploration geophysics::04.02.99. General or miscellaneous ; 04. Solid Earth::04.03. Geodesy::04.03.99. General or miscellaneous ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.07. Tectonophysics::04.07.99. General or miscellaneous ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions ; 05. General::05.04. Instrumentation and techniques of general interest::05.04.99. General or miscellaneous ; 05. General::05.08. Risk::05.08.99. General or miscellaneous
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  • 30
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    A buried volcano in the Calabrian Arc (Italy) revealed by high‐resolution aeromagnetic data (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Aeromagnetic data collected between the Aeolian volcanoes (southern Tyrrhenian Sea) and the Calabrian Arc (Italy) highlight a WNW‐ESE elongated positive magnetic anomaly centered on the Capo Vaticano morphological ridge (Tyrrhenian coast of Calabria), characterized by an apical, subcircular, flat surface. Results of forward and inverse modeling of the magnetic data show a 20 km long and 3–5 km wide magnetized body that extends from sea floor to about 3 km below sea level. The magnetic properties of this body are consistent with those of the medium to highly evolved volcanic rocks of the Aeolian Arc (i.e., dacites and rhyolites). In the Calabria mainland, widespread dacitic to rhyolitic pumices with calc‐alkaline affinity of Pleistocene age (1–0.7 Ma) are exposed. The tephra falls are related to explosive activity and show a decreasing thickness from the Capo Vaticano area southeastward. The presence of lithics indicates a provenance from a source located not far from Capo Vaticano. The combined interpretation of the magnetic and available geological data reveal that (1) the Capo Vaticano WNW‐ESE elongated positive magnetic anomaly is due to the occurrence of a WNW‐ESE elongated sill; (2) such a sill represents the remnant of the plumbing system of a Pleistocene volcano that erupted explosively producing the pumice tephra exposed in Calabria; and (3) the volcanism is consistent with the Aeolian products, in terms of age, magnetic signature, and geochemical affinity of the erupted products,. The results indicate that such volcanism developed along seismically active faults transversal to the general trend of the Aeolian Arc and Calabria block, in an area where uplift is maximized (∼4 mm/yr). Such uplift could also be responsible for fragmentation of the upper crust and formation of transversal faults along which seismic activity and volcanism occur.
    Description: Published
    Description: B11101
    Description: 3.2. Tettonica attiva
    Description: 3.4. Geomagnetismo
    Description: 5.7. Consulenze in favore di istituzioni nazionali e attività nell'ambito di trattati internazionali
    Description: JCR Journal
    Description: restricted
    Keywords: aeromagnetic anomalies ; volcanic arc ; tectonics of the Calabrian Arc ; risk assessment ; 04. Solid Earth::04.02. Exploration geophysics::04.02.99. General or miscellaneous ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.07. Tectonophysics::04.07.08. Volcanic arcs
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  • 31
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    Focal mechanisms for sub‐crustal earthquakes in the Gulf of Cadiz from a dense OBS deployment (2010)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: An eleven‐month deployment of 25 ocean bottom seismometers provides an unprecedented opportunity to study low‐magnitude local earthquakes in the complex transpressive plate boundary setting of the Gulf of Cadiz, known for the 1755 Lisbon earthquake and tsunami. 36 relocated earthquakes (ML 2.2 to 4.8) concentrate at 40– 60 km depth, near the base of the seismogenic layer in ∼140 Ma old oceanic mantle lithosphere, and roughly align along two perpendicular, NNE‐SSW and WNWESE striking structures. First motion focal mechanisms indicate compressive stress for the cluster close to the northern Horseshoe fault termination which trends perpendicular to plate convergence. Focal mechanisms for the second cluster near the southern termination of the Horseshoe fault indicate a strike‐slip regime, providing evidence for present‐day activity of a dextral shear zone proposed to represent the Eurasia‐Africa plate contact. We hypothesize that regional tectonics is characterized by slip partitioning.
    Description: Published
    Description: L18309
    Description: 3.1. Fisica dei terremoti
    Description: 3.2. Tettonica attiva
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: oceanic lithospheric mantle ; focal mechanisms ; stress tensor inversion ; Gulf of Cadiz ; ocean bottom seismometer ; 1755 Lisbon earthquake ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
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  • 32
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    Characterization of GPS time series at the Neapolitan volcanic area by statistical analysis (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: The GPS time series recorded at the Neapolitan volcanic area reveals a very peculiar behavior. When a clear deformation is observed, the amplitude distribution evolves from a super‐Gaussian to a broader distribution. This behavior can be characterized by evaluating the kurtosis. Spurious periodic components were evidenced by independent component analysis and then removed by filtering the original signal. The time series for all stations was modeled with a fifth‐order polynomial fit, which represents the deformation history at that place. Indeed, when this polynomial is subtracted from the time series, the distributions again become super‐Gaussian. A simulation of the deformation time evolution was performed by superposing a Laplacian noise and a synthetic deformation history. The kurtosis of the obtained signals decreases as the superposition increases, enlightening the insurgence of the deformation. The presented approach represents a contribution aimed at adding further information to the studies about the deformation at the Neapolitan volcanic area by revealing geologically relevant data.
    Description: Published
    Description: B10416
    Description: 1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: GPS time series ; Neapolitan volcanic ; statistical analysis ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
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  • 33
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    Predicting the impact of lava flows at Mount Etna (Italy) (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Forecasting the time, nature and impact of future eruptions is difficult at volcanoes such as Mount Etna, in Italy, where eruptions occur from the summit and on the flanks, affecting areas distant from each other. Nonetheless, the identification and quantification of areas at risk from new eruptions is fundamental for mitigating potential human casualties and material damage. Here, we present new results from the application of a methodology to define flexible high-resolution lava invasion susceptibility maps based on a reliable computational model for simulating lava flows at Etna and on a validation procedure for assessing the correctness of susceptibility mapping in the study area. Furthermore, specific scenarios can be extracted at any time from the simulation database, for land-use and civil defence planning in the long-term, to quantify, in real-time, the impact of an imminent eruption, and to assess the efficiency of protective measures.
    Description: This work was sponsored by the Italian Ministry for Education, University and Research, FIRB project n° RBAU01RMZ4 “Lava flow simulations by Cellular Automata”, and by the National Civil Defence Department and INGV (National Institute of Geophysics and Volcanology), project V3_6/09 “V3_6 – Etna”.
    Description: In press
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 4.4. Scenari e mitigazione del rischio ambientale
    Description: JCR Journal
    Description: open
    Keywords: lava flows ; Etna ; hazard evaluation ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous ; 05. General::05.01. Computational geophysics::05.01.02. Cellular automata, fuzzy logic, genetic alghoritms, neural networks ; 05. General::05.02. Data dissemination::05.02.99. General or miscellaneous ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions ; 05. General::05.08. Risk::05.08.99. General or miscellaneous ; 05. General::05.09. Miscellaneous::05.09.99. General or miscellaneous
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  • 34
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    Submarine Hydrothermal Activity on the Aeolian Arc: New evidence from Helium Isotopes (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In November 2007 we conducted a water-column and seafloor mapping study of the submarine volcanoes of the Aeolian Arc in the southern Tyrrhenian Sea aboard the R/V Urania. A total of 26 CTD casts were completed, 13 vertical casts and 13 tows. In addition to in situ measurements of temperature, conductivity, pressure and suspended particles, we also collected discrete samples for helium isotopes, methane, and trace metals. The helium isotope ratio, which is known to be an unambiguous indicator of hydrothermal input, showed a clear excess above background at 5 out of the 10 submarine volcanoes surveyed. We found the strongest helium anomaly over Marsili seamount, where the 3He/4He ratio reached maximum values of 3He = 23% at 610 m depth compared with background values of ~ 7%. We also found smaller but distinct 3He anomalies over Enerato, Eolo, Palinuro, and Secca del Capo. We interpret these results as indicating the presence of hydrothermal activity on these 5 seamounts. Hydrothermal venting has been documented at subsea vents offshore of the islands of Panarea, Stromboli, and Vulcano (Dando et al., 1999; Di Roberto et al., 2008), and hydrothermal deposits have been sampled on many of the submarine volcanoes of the Aeolian Arc (Dekov and Savelli, 2004). However, as far as we know this is the first evidence of present day hydrothermal activity on Marsili, Enerato, and Eolo. Samples collected over Filicudi, Glabro, Lamentini, Sisifo, and Alcioni had 3He very close to the regional background values, suggesting either absence of or very weak hydrothermal activity on these seamounts. Helium isotope measurements from the background hydrocasts positioned between the volcanoes revealed the presence of an excess in 3He throughout the SE Tyrrhenian Sea. These background profiles reach a consistent maximum of about 3He = 11% at 2300 m depth. Historical helium profiles collected in the central and northern Tyrrhenian Sea in 1987 and 1997 do not show this deep 3He maximum (W. Roether and B. Klein, private comm.). Furthermore, the maximum is too deep to be attributed to the volcanoes of the Aeolian Arc, which are active at 〈1000 m depth. We are currently conducting additional measurements to determine whether this deep 3He maximum is from a local hydrothermal source or is somehow related to the deep water mass transient which occurred in the eastern Mediterranean in the 1990’s.
    Description: American Geophysical Union
    Description: Published
    Description: San Francisco
    Description: 4.6. Oceanografia operativa per la valutazione dei rischi in aree marine
    Description: open
    Keywords: submarine ; hydrothermalism ; helium isotopes ; 04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration
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  • 35
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    Long term variations at Campi Flegrei (Italy) volcanic system highlighted by the monitoring of hydrothermal activity (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Long duration time-series of the chemical composition of fumaroles and of soil CO2 flux reveal that important variations in the activity of the Solfatara fumarolic field, the most important hydrothermal site of Campi Flegrei, occurred in the 2000-2008 period. A continuous increase of the CO2 concentrations, and a general decrease of the CH4 concentrations are interpreted as the consequence of the increment of the relative amount of magmatic fluids, rich in CO2 and poor in CH4, hosted by the hydrothermal system. Contemporaneously, the H2O-CO2-He-N2 gas system shows remarkable compositional variations in the samples collected after July 2000 with respect to the previous ones, indicating the progressive arrival at the surface of a magmatic componentdifferent from that involved in the 1983-84 episode of volcanic unrest (1983-1984 bradyseism). The change starts in 2000 concurrently with the occurrence of relatively deep, long-period seismic events which were the indicator of the opening of an easy-ascent pathway for the transfer of magmatic fluids towards the shallower, brittle domain hosting the hydrothermal system. Since 2000, this magmatic gas source is active and causes ground deformations, seismicity as well as the expansion of the area affected by soil degassing of deeply derived CO2. Even though the activity will most probably be limited to the expulsion of large amounts of gases and thermal energy, as observed in other volcanoes and in the past activity of Campi Flegrei, the behavior of the system in the future is, at the moment, unpredictable.
    Description: In press
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: JCR Journal
    Description: open
    Keywords: Solfatara crater ; CO2 content ; hydrothermal system ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 36
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    Heterogeneous large total CO2 abundance in the shallow magmatic system of Kilauea volcano, Hawaii (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Due to its very low solubility in silicate melts, CO2 concentrations in melt inclusions (MIs) within crystals are commonly orders of magnitude less than the total concentration in the multiphase magma, strongly limiting the possibility to constrain CO2 abundance based on the dissolved quantities. Here we develop a statistical method to process MI data, which allows analytical uncertainties to be taken into account together with the peculiar features of the local saturation surface. The method developed leads to retrieve total H2O and CO2 concentrations in magma as well as the gas phase abundance at the time of magma crystallization. Application to a set of 29 high-resolution secondary ion mass spectrometry (SIMS) MI data from a single specimen of the 1842–1844 eruption of Kilauea, Hawaii, reveals the existence of heterogeneous total CO2 abundance, and of at least 2–6 wt % total CO2 in some magma batches, two orders of magnitude higher than the dissolved amounts and 30–50 times more abundant than the corresponding total H2O content. Heterogeneous total volatile concentrations are interpreted as due to a combination of degassing and gas flushing in magma subject to convective motion at shallow depth where P 〈 100 MPa. In such a view, the magma rising to shallow depth in the volcanic system carries initially a total volatile content ≤1 wt %, corresponding to the determined low total CO2 population, and consistent with previous global estimates. The high CO2 populations correspond to progressive CO2 enrichment due to degassing at low P and flushing from a deep CO2-rich gas. A total CO2 content 〉1 wt % is likely to characterize the 〉30 km deep magma, not represented in the analyzed inclusions, from which a CO2-rich gas phase exsolves and decouples from the liquid.
    Description: Published
    Description: B12201
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: carbon dioxide ; Kilauea volcano ; conduit dynamics ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
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  • 37
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    CO2/CH4 ratio in fumaroles a powerful tool to detect magma degassing episodes at quiescent Volcanoes (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Long time series of fumarolic compositions at Campi Flegrei (Italy), Mammoth Mountain (California), Panarea (Italy) and Nisyros (Greece) show rapid increases, up to orders of magnitude, of the CO2/CH4 ratio systematically with the occurrence of volcanic unrest periods. These easily detected anomalies originate with the arrival of CH4-poor magmatic fluids in the shallower levels of the volcanoes. The data suggest that volcanoes are characterized by magmatic activity at depth also in periods of apparent quiescence. The activity is constituted by the pulsing release of large amount of fluids which either cause unrest periods (seismicity and ground deformation) or possibly could precede volcanic eruption. This type of volcanic activity can be monitored trough the classical geophysical techniques together with the systematic sampling and analysis of fumaroles.
    Description: Published
    Description: L02302
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: 2.4. TTC - Laboratori di geochimica dei fluidi
    Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi
    Description: JCR Journal
    Description: reserved
    Keywords: CO2/CH4 ; magma degassing ; quiescent volcanoes ; 03. Hydrosphere::03.04. Chemical and biological::03.04.05. Gases ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
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  • 38
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    Signals from the Campi Flegrei hydrothermal system: Role of a ‘‘magmatic’’ source of fluids (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: This is a parametric study that was carried out to investigate the signals generated by a hydrothermal system fed by a pulsating source of magmatic fluids. This study focuses on the effects that selected properties of the source have on the evolution of hydrothermal activity at Campi Flegrei, Italy. Numerical simulations are carried out to describe a multiphase and multicomponent hydrothermal system. Each simulation describes a short unrest phase, followed by a prolonged quiet period. During the unrest, specific properties of the fluid source (flow rate, fluid composition, source size, and unrest duration) are modified with respect to selected baseline values. The evolution of the system is tracked by looking at two parameters that can be monitored in active volcanic areas: the composition of fumarolic gases and gravity changes. The results describe the temporal evolution of these two observables and allow comparisons of the effects of different source properties. All of the simulated unrest events cause measurable changes in gas composition and gravity. For the geometry and system properties considered, these changes always last beyond the end of the unrest period, and can often persist for decades. Fluid flow rate is the source property that mostly affects the observable evolution. Gravity is more sensitive to source properties than gas composition, and it undergoes the largest and quickest changes. The results also highlight the major role that rock properties and initial conditions have in the evolution of these observable signals.
    Description: Department of Civil Protection
    Description: Published
    Description: B05201
    Description: 3.6. Fisica del vulcanismo
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: hydrothermal fluids ; modeling ; monitoring ; signals ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 39
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    Intermediate-focus earthquakes under South Shetland Islands (Antarctica) (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Intermediate-focus seismicity (50〈H〈100km) related to the underplating zone of the South Shetland plate have been recorded at a small aperture seismic array set up in Deception Island, Antarctica.
    Description: Published
    Description: 531-534
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Deep earthquakes ; Antarctica ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 40
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    Array tracking of the volcanic tremor source at Deception Island Antarctica (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We have found experimental evidence which shows that the volcanic tremor recorded at Deception Island (South Shetland Islands, Antarctica) is a superposition in time of overlapping hybrid events.
    Description: Published
    Description: 3069-3072
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Arrays ; volcanictremor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 41
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    On the mechanism of seasonal and solar cycle NmF2 variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Seasonal (winter/summer) and solar cycle NmF2 variations as well as summer saturation effect in NmF2 have been analyzed using Millstone Hill incoherent scatter radar (ISR) daytime observations. A self‐consistent approach to the Ne(h) modeling has been applied to extract from ISR observations a consistent set of main aeronomic parameters and to estimate their quantitative contribution to the observed NmF2 variations. The retrieved aeronomic parameters are independent of uncertainties in thermosphere and solar EUV empirical models, and this is a distinguishing feature of the present consideration. Different temperatures in winter and in summer in the course of solar cycle overlapped on the O++N2 reaction rate coefficient temperature dependence result in different NmF2 dependences on solar activity: a steep practically linear increase with a tendency to turn up in January (contrary to international reference ionosphere prediction) and a slow increase with a tendency to saturate at high solar activity in July despite increasing solar EUV irradiation. In winter the EUV flux and thermospheric parameters provide approximately equal contributions to the NmF2 increase, while in summer the contribution of thermospheric parameters is small. Both in winter and in summer the variations of atomic oxygen [O] are small at the F2 layer peak, and its contribution is small compared to linear loss coefficient, b. It is shown that the summer saturation effect in NmF2 under high solar activity is not just reduced to O/N2 or EUV flux solar cycle variations but is determined by b via the g1 temperature dependence. A new mechanism (qualitative) to explain the December anomaly in NmF2 is proposed. It is based on the idea that the areas of atomic oxygen production and its loss are spatially separated and that time is required to transfer [O] from one area to the other where [O] associates in a three‐body collision. Therefore, under a 7% increase in the O2 dissociation rate due to the Sun‐Earth distance decrease in December–January compared to June–July, an accumulation of atomic oxygen should take place in the thermosphere in the vicinity of the December solstice resulting in a 21% NmF2 increase, which is close to the observed global December effect.
    Description: Published
    Description: A03319
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: mid-latitude ionosphere ; thermosphere composition and chemistry ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.01. Ion chemistry and composition ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics
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    An information theory approach to the storm‐substorm relationship (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One of the most interesting aspects of the global magnetospheric response to solar wind changes is the relationship between storms and substorms. Here we present new results on the relationship between these two different classes of magnetospheric phenomena by approaching the problem on the side of information theory. Using the Auroral Electrojet AL and SYM‐H indices as representative proxies of magnetic substorms and storms, we investigate the transfer of information by means of transfer entropy analysis (Schreiber, 2000). The obtained results seem, on average, to indicate the presence of a net transfer of information from AL to SYM‐H on time scales shorter than 10 h. On the basis of this result, geomagnetic substorms may act as a driver for the occurrence of geomagnetic storms. However, carrying out a more careful analysis which takes into account the global geomagnetic daily activity, we suggest that the direction of information flow between substorms and storms depends on the global activity level. Indeed, if it is true that a sequence of magnetospheric substorms may drive a moderate storm, it is also true that very large storms may dominate and drive the occurrence of magnetospheric substorms.
    Description: Published
    Description: A08225
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: Storm-substorm relationship ; Information theory ; 01. Atmosphere::01.03. Magnetosphere::01.03.02. Magnetic storms ; 01. Atmosphere::01.03. Magnetosphere::01.03.03. Magnetospheric physics ; 05. General::05.01. Computational geophysics::05.01.04. Statistical analysis
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  • 43
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    Detecting young, slow‐slipping active faults by geologic and multidisciplinary high‐resolution geophysical investigations: A case study from the Apennine seismic belt, Italy. (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The Southern Apennines range of Italy presents significant challenges for active fault detection due to the complex structural setting inherited from previous contractional tectonics, coupled to very recent (Middle Pleistocene) onset and slow slip rates of active normal faults. As shown by the Irpinia Fault, source of a M6.9 earthquake in 1980, major faults might have small cumulative deformation and subtle geomorphic expression. A multidisciplinary study including morphological-tectonic, paleoseismological, and geophysical investigations has been carried out across the extensional Monte Aquila Fault, a poorly known structure that, similarly to the Irpinia Fault, runs across a ridge and is weakly expressed at the surface by small scarps/warps. The joint application of shallow reflection profiling, seismic and electrical resistivity tomography, and physical logging of cored sediments has proved crucial for proper fault detection because performance of each technique was markedly different and very dependent on local geologic conditions. Geophysical data clearly (1) image a fault zone beneath suspected warps, (2) constrain the cumulative vertical slip to only 25–30 m, (3) delineate colluvial packages suggesting coseismic surface faulting episodes. Paleoseismological investigations document at least three deformation events during the very Late Pleistocene (〈20 ka) and Holocene. The clue to surface-rupturing episodes, together with the fault dimension inferred by geological mapping and microseismicity distribution, suggest a seismogenic potential of M6.3. Our study provides the second documentation of a major active fault in southern Italy that, as the Irpinia Fault, does not bound a large intermontane basin, but it is nested within the mountain range, weakly modifying the landscape. This demonstrates that standard geomorphological approaches are insufficient to define a proper framework of active faults in this region. More in general, our applications have wide methodological implications for shallow imaging in complex terrains because they clearly illustrate the benefits of combining electrical resistivity and seismic techniques. The proposed multidisciplinary methodology can be effective in regions characterized by young and/or slow slipping active faults.
    Description: Published
    Description: B11307
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: partially_open
    Keywords: active fault ; integrated geophysical investigations ; morpho-tectonic analysis ; paleoseismology ; Val d'Agri ; Southern Italy ; 1857 Earthquake ; 04. Solid Earth::04.02. Exploration geophysics::04.02.04. Magnetic and electrical methods ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods ; 04. Solid Earth::04.02. Exploration geophysics::04.02.07. Instruments and techniques ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.04. Geology::04.04.11. Instruments and techniques
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  • 44
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    New insights into banded tremor from the 2008–2009 Mount Etna eruption (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We investigated the banded tremor activity occurring at Mt. Etna volcano between August-October 2008 during the 2008-2009 eruption. The banded tremor occurred in episodes lasting 25-30 minutes with intervals in between the episodes of about 25 minutes. Seismic signal analyses showed that the banded tremor was characterised by spectral contents, wavefields and source locations that differed from the “ordinary” volcanic tremor. The infrasound recordings exhibited an intermittent infrasonic tremor alternating with the banded tremor episodes. Finally, nonlinear analyses suggested that banded tremor system can be considered chaotic, implying: i) sensitive dependence on initial conditions, suggesting not only that a banded tremor system requires particular conditions to generate, but also that slight variations of these conditions are able to greatly change the features of the banded tremor or even to stop it; ii) long-term unpredictability, that is, the impossibility to forecast the long-term evolution of the banded tremor. On the basis of all these results and analogies with geyser models, we suggest a model of banded tremor that invokes alternating recharge-discharge phases. Banded tremor is due to “perturbations” in shallow aquifers, such as fluid movement and bubble growth or collapse due to hydrothermal boiling, triggered by the heat and hot fluid transfer from the underlying magma bodies. This heat-fluid transfer also causes an increasing pressure in the aquifer leading to fluid-discharge. During this process the seismic radiation decreases and, if the fluid-discharge is well coupled with the atmosphere, acoustic signals are generated.
    Description: Published
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Banded tremor ; Mt. Etna volcano ; volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 45
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    Active tectonics in Northern Victoria Land (Antarctica) inferred from the integration of GPS data and geologic setting. (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Accepted for publication in Journal of Geophysical Research. Copyright (2010) American Geophysical Union.
    Description: A semi-permanent global positioning system (GPS) network of 30 vertices known as the Victoria Land Network for Deformation Control (VLNDEF) was set-up in the Austral summer of 1998 in Northern Victoria Land (NVL), including Terra Nova Bay (TNB), Antarctica. The locations were selected according to the known Cenozoic fault framework that is characterized by a system of NW-SE regional faults with right-lateral, strike-slip kinematics. The TNB1 permanent GPS station is within the VLNDEF, and following its installation on a bedrock monument in October 1998 it has been recording almost continuously. The GPS network has been surveyed routinely every two summers, using high-quality, dual-frequency GPS receivers. In this study, we present the results of a distributed session approach applied to the processing of the GPS data of the VLNDEF. An improved reference frame definition was implemented, including a new Euler pole, to compute the Antarctic intra-plate residual velocities. The projection of the residual velocities on the main faults in NVL show present-day activities for some faults, including the Tucker, Leap Year, Lanterman, Aviator, and David faults, with rightlateral strike-slip kinematics and local extensional/ compressional components. This active fault pattern divides NVL into eight rigid blocks, each characterized by their relative movements and rigid rotations. These show velocities of up to several mm/yr, which are comparable to those predicted by plate tectonic theory at active plate margins.
    Description: All researches were carried out in the framework of the Programma Nazionale di Ricerche in Antartide (PNRA) and financially supported by PNRA S.C.r.l.
    Description: Published
    Description: B12421
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: ANTARCTICA ; GEODESY ; MONITORING NETWORKS ; CRUSTAL DEFORMATION ; CONTINENTAL NEOTECTONICS ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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    Water vapor sounding with the far infrared REFIR-PAD spectroradiometer from a high-altitude ground-based station during the ECOWAR campaign (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The REFIR-PAD spectroradiometer was operated from the Testa Grigia Italian-Alps station in March 2007 during the Earth COoling by WAter vapouR emission (ECOWAR) measurement campaign, obtaining downwelling radiance spectra in the 100-1100 cm−1 range, under clear-sky condition and in the presence of cirrus clouds. The analysis of these mea surements has proven that the instrument is capable of determining precipitable water vapor with a total uncertainty of 5–7% by using the far-infrared rotational band of water. The measurement is unaffected by the presence of cirri, whose optical depth can be instead retrieved as an additional parameter. Information on the vertical profiles of water vapor volume mixing ratio and temperature can also be retrieved for three altitude levels. The ability to measure the water vapor column with a simple, uncooled instrument, capable of operating continuously and with a time resolution of about 10 minutes makes REFIR-PAD a very valuable instrument for meteorological and climatological studies for the characterization of the water vapor distribution.
    Description: In press
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 1.10. TTC - Telerilevamento
    Description: JCR Journal
    Description: restricted
    Keywords: tropospheric water vapor ; IR spectroscopy ; REFIR-PAD ; ECOWAR ; 01. Atmosphere::01.01. Atmosphere::01.01.01. Composition and Structure ; 01. Atmosphere::01.01. Atmosphere::01.01.08. Instruments and techniques
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  • 47
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    Bipolar climatology of GPS ionospheric scintillation at solar minimum (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: High-rate sampling data of GNSS (Global Navigation Satellite Systems) ionospheric scintillation acquired by a network of GISTM (GPS Ionospheric Scintillation and TEC Monitor) receivers located in the Svalbard Islands, in Norway and in Antarctica have been analyzed. The aim is to describe the “scintillation climatology” of the high latitude ionosphere over both the poles under quiet conditions of the near-Earth environment. For climatology we mean to assess the general recurrent features of the ionospheric irregularities dynamics and temporal evolution on long data series, trying to catch eventual correspondences with scintillation occurrence. In spite of the fact that the sites are not geomagnetically conjugate, long series of data recorded by the same kind of receivers provide a rare opportunity to draw a picture of the ionospheric features characterizing the scintillation conditions over high latitudes. The method adopted is the Ground Based Scintillation Climatology, which produces maps of scintillation occurrence and of TEC relative variation to investigate ionospheric scintillations scenario in terms of geomagnetic and geographic coordinates, Interplanetary Magnetic Field conditions and seasonal variability. By means of such a novel and original description of the ionospheric irregularities, our work provides insights to speculate on the cause-effect mechanisms producing scintillations, suggesting the roles of the high latitude ionospheric trough, of the auroral boundaries and of the polar cap ionosphere in hosting those irregularities causing scintillations over both the hemispheres at high latitude. The method can constitute a first step towards the development of new algorithms to forecast the scintillations during space weather events.
    Description: Published
    Description: RS0D05
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: ionospheric scintillations ; climatology ; high latitude ionosphere ; space weather ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.07. Scintillations ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 48
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    Forearc extension and slow rollback of the Calabrian Arc from GPS measurements (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Here we describe the horizontal velocities of continuous GPS stations in the Calabrian Arc (CA) and surrounding regions. The appropriate reference frame to evaluate the crustal motion of the CA is considered by assessing the internal deformation and the relative motion of the crustal blocks in the foreland of the Apennines␣Ionian␣Maghrebides subduction system. We propose that the motion of CA rela- tive to the subducting Ionian lower plate is most properly assessed by minimizing the GPS velocities in Apulia. In this reference frame the significant ␣2 mm/yr southeast- ward motion of the stations on the Ionian flank of the CA shows that the arc is still moving towards the trench in agreement with the observations of active shortening in the Ioanian wedge. This southeastward migration is associated to 1.4 ± 0.3 mm/yr E␣W extension of the forearc in northern Calabria, comparable with the seismic strain averaged in the last 500 years. The limited subaerial exposure decreases the resolution on locking of the subduction interface but the distribution and direction of crustal extension along the CA impose important constraints on geodynamic interpreta- tions of the area.
    Description: Published
    Description: L17304
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: Calabrian Arc ; GPS ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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    Evidence for surface faulting events along the Paganica fault prior to the 6 April 2009 L’Aquila earthquake (central Italy) (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: main article
    Description: We performed paleoseismological investigations at four sites across the normal Paganica fault (PF) (source of the 2009 Mw 6.3 L’Aquila earthquake), with the goal of reconstructing the rupture history and of contributing to the evaluation of the maximum event expected along the PF. We recognized five distinct surface faulting earthquakes (including the 2009) in the trenches. The age of the penultimate event is consistent with the 1461 earthquake; the third event back occurred around 1000 AD. The two oldest events have larger uncertainties and occurred in the interval 760 BC–670 AD and 2900–760 BC, respectively. The along‐strike vertical displacement for each paleoevent has a limited variability consistently with the fairly homogeneous slip observed in 2009 along the northern part of the rupture. Conversely, the throws change between distinct events and range between 0.15 m in 2009 (maximum estimate) and close to 0.4 (lower bound estimate) in earlier events. These paleorecords and the high fault escarpments imply that earthquakes larger than 2009 occurred on the PF, with implications for the level of hazard. Recurrence intervals also reflect a change with time, the average interval before ∼1000 AD is longer compared to that after this date. Two events occurred in the 2000– 4000 years preceding ∼1000 AD, while three events occurred since ∼1000 AD. The age uncertainties affecting the interpreted events prevent the evaluation of a unique value for interevent interval; the older events appear closely spaced in time or far apart depending on the upper or lower boundary of the age interval. We tentatively assign an average interevent time of ∼500 years for the three youngest events, whereas the time elapsed between the previous ones could be larger, in the order of 1000–2000 years. We calculate a late Pleistocene dip‐slip rate for the PF of 0.2–0.4 mm/yr, consistent with 0.25–0.5 mm/yr for the early Pleistocene. Using age and throw of individual events, we calculate a similar late Holocene average dip‐slip rate of ∼0.3–0.4 mm/yr. This suggests that the portion of the PF where the 2009 continuous surface faulting occurred has fairly a constant average slip release since late Pleistocene. Finally, we discuss different rupture scenarios and alternative models of occurrence compatible with our data and their variability.
    Description: This work was partially funded by the Italian Dipartimento della Protezione Civile in the frame of the 2007–2009 Agreement with Istituto Nazionale di Geofisica e Vulcanologia (INGV).
    Description: Published
    Description: B07308
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: reserved
    Keywords: 2009 L'Aquila seismic sequence ; paleoearthquakes ; Paganica fault ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
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  • 50
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    Late Quaternary sediments from deep!sea sediment drifts on the Antarctic Peninsula Pacific margin: Climatic control on provenance of minerals (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present results of detailed paleomagnetic investigations on deep!sea cores from sediment drifts located along the Pacific continental margin of the Antarctic Peninsula. High!resolution magnetic measurements on u channel samples provide detailed age models for three cores collected from drift 7, which document an age of 122 ka for the oldest sediments recovered near the drift crest at site SED!07 and a high sedimentation rate (11 cm/kyr) at site SED!12 located close to the Alexander Channel system. Low! and high!temperature magnetic measurements in conjunction with microscopic and mineralogic observations from drifts 4, 5 and 7 indicate that pseudosingle!domain detrital titanomagnetite (partially oxidized and with limited Ti substitution) is the dominant magnetic mineral in the drift sediments. The titanomagnetite occurs in two magnetic forms: (1) a low!coercivity form similar to laboratory!synthesized titanomagnetite and (2) a high!coercivity form (Bcr 〉 60 mT). These two forms vary in amount and stratigraphic distribution across the drifts. We did not find evidence for diagenetic magnetic iron sulfides as has been previously suggested for these drift deposits. The observed change of magnetic mineralogy in sediments deposited during Heinrich events on drift 7 appears to be related to warming periods, which temporarily modified the normal glacial transport pathways of glaciogenic detritus to and along the continental rise and thus resulted in deposition of sediments with a different provenance. Understanding this sediment provenance delivery signature at a wider spatial scale should provide information about ice sheet dynamics in West Antarctica over the last !100 kyr.
    Description: Published
    Description: B06104
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: partially_open
    Keywords: Antarctic Peninsula ; Pacific margin ; sediment drift ; late Pleistocene ; Mineral magnetism ; relative palaeointensity ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
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    A new extended software package for quantitative paleoenvironmental reconstrutions (1999)
    American Geophysical Union
    In:  EPIC3EOS, Transactions of the American Geophysical Union, American Geophysical Union, 80(19), 223 p., pp. 223-223
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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    Thirty years of satellite‐derived lava discharge rates at Etna: Implications for steady volumetric output (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: We present a 30 year long data set of satellite‐derived time‐averaged lava discharge rates (TADR) for Mount Etna volcano (Sicily, Italy), spanning 1980–2010 and comprising 1792 measurements during 23 eruptions. We use this to classify eruptions on the basis of magnitude and intensity, as well as the shape of the TADR time series which characterizes each effusive event. We find that while 1983–1993 was characterized by less frequent but longer‐duration effusive eruptions at lower TADRs, 2000–2010 was characterized by more frequent eruptions of shorter duration and higher TADRs. However, roughly the same lava volume was erupted during both of these 11 year long periods, so that the volumetric output was linear over the entire 30 year period, increasing at a rate of 0.8 m3 s−1 between 1980 and 2010. The cumulative volume record can be extended back in time using data available in the literature. This allows us to assess Etna’s output history over 5 centuries and to place the current trend in historical context. We find that output has been stable at this rate since 1971. At this time, the output rate changed from a low discharge rate phase, which had characterized the period 1759 to 1970, to a high discharge rate phase. This new phase had the same output rate as the high discharge rate phase that characterized the period 1610–1669. The 1610–1669 phase ended with the most voluminous eruption of historic times.
    Description: This contribution is in support of the LMV‐based (PI: Franck Donnadieu) TerMex‐MYSTRALS project “Contribution à l’évaluation des risques associés aux activités éruptives majeures de l’Etna: approche multidisciplinaire des processus et précurseurs.”
    Description: Published
    Description: B08204
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: partially_open
    Keywords: Etna ; time averaged effusion rate ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
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    Modeling of unrest signals in heterogeneous hydrothermal systems (2010)
    American Geophysical Union
    Details
    Publication Date: 2019-10-10
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Monitoring of quiescent volcanoes, such as Campi Flegrei (Italy), involves the measurement of geochemical and geophysical parameters that are expected to change as eruptive conditions approach. Some of these changes are associated with the hydrothermal activity that is driven by the release of heat and magmatic fluids. This work focuses on the properties of the porous medium and on their effects on the signals generated by the circulating fluids. The TOUGH2 porous media flow model is applied to simulate a shallow hydrothermal system fed by a source of magmatic fluids. The simulated activity of the source, with periods of increased fluid discharge, generates changes in gas composition, gravity, and ground deformation. The same boundary conditions and source activity were applied to simulate the evolution of homogeneous and heterogeneous systems, characterized by different rock properties. Phase distribution, fluid composition, and the related signals depend on the nature and properties of the rock sequence through which the fluids propagate. Results show that the distribution of porosity and permeability affects all the observable parameters, controlling the timing and the amplitude of their changes through space and time. Preferential pathways for fluid ascent favor a faster evolution, with larger changes near permeable channels. Slower changes over wider areas characterize less permeable systems. These results imply that monitoring signals do not simply reflect the evolution of the magmatic system: intervening rocks leave a marked signature that should be taken into account when monitoring data are used to infer system conditions at depth.
    Description: This work was carried out within the research project V1-UNREST, founded by the Italian Civil Protection Department
    Description: Published
    Description: B09213
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: open
    Keywords: hydrothermal circulation ; observable ; volcanic unrest ; permeability ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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    Shallow structure of Mt. Vesuvius volcano, Italy, from seismic array analysis (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-05-23
    Description: SPAC method applied to data from a small aperture seismic array on Mt. Vesuvius gives the shallow velocity model.
    Description: Published
    Description: 481-484
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Array analysis ; shallow structure ; SPAC method ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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    Source Mechanism of Long Period events recorded by a high density seismic network during the 2008 eruption on Mt Etna (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: 129 Long Period (LP) events, divided in two families were recorded by 50 stations deployed on Mount Etna within an eruptive context in the second half of June 2008. In order to understand the mechanisms of these events, we perform moment tensor inversion. Numerical tests show that unconstrained inversion leads to reliable moment tensor solutions because of the close proximity of numerous stations to the source positions. However, single forces cannot be accurately determined as they are very sensitive to uncertainities in the velocity model. These tests emphasize the importance of using stations located as close as possible to the source in the inversion of LP events. Inversion of LP signals is initially unconstrained, in order to estimate the most likely mechanism. Constrained inversions then allow us to accurately determine the structural orientations of the mechanisms. Inversions for both families show mechanisms with strong volumetric components. These events are generated by cracks striking SW-NE for both families and dipping 70± SE (fam. 1) and 50± NW (fam. 2). The geometries of the cracks are different from the structures obtained by the location of these events. The orientation of the cracks is consistent with the local tectonic context on Mount Etna. The LP events seem to be a response to the lava fountain occuring on the 10th of May, 2008.
    Description: In press
    Description: (38)
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: Long-Period events ; earthquake source mechanism ; Etna Volcano ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 56
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    Kinematics and source zone properties of the 2004 Sumatra-Andaman earthquake and tsunami: Nonlinear joint inversion of tide gauge, satellite altimetry, and GPS data (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We (re)analyzed the source of the 26 December 2004 Sumatra-Andaman earthquake and tsunami through a nonlinear joint inversion of an inhomogeneous data set made up of tide gauges, satellite altimetry, and far-field GPS recordings. The purpose is twofold: (1) the retrieval of the main kinematics rupture parameters (slip, rake, and rupture velocity) and (2) the inference of the rigidity of the source zone. We independently estimate the slip from tsunami data and the seismic moment from geodetic data to derive the rigidity. Our results confirm that the source of the 2004 Sumatra-Andaman earthquake has a complex geometry, constituted by three main slip patches, with slip peaking at ~30 m in the southern part of the source. The rake direction rotates counterclockwise at the northern part of the source, according to the direction of convergence along the trench. The rupture velocity is higher in the deeper than in the shallower part of the source, consistent with the expected increase of rigidity with depth. It is also lower in the northern part, consistent with known variations of the incoming plate properties and shear velocity. Our model features a rigidity (20–30 GPa) that is lower than the preliminary reference Earth model (PREM) average for the seismogenic volume. The source rigidity is one of the factors controlling the tsunami genesis: for a given seismic moment, the lower the rigidity, the higher the induced seafloor displacement. The general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation.
    Description: Published
    Description: B02304
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Source process ; Sumatra ; Tsunami ; Joint Inversion ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 57
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    Radon and thoron emission from lithophysae-rich tuff under increasing deformation: An experimental study (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Radon and thoron emissions from lithophysae‐rich tuff under increasing deformation are measured to determine how mechanical damage affects gas emission levels in tuffs. Mechanical properties of rocks under stresses should be carefully considered to properly interpret data from geochemical field monitoring. Two samples are uniaxially loaded up to failure, while two others are unloaded at the end of the elastic phase, in order to achieve the highest compaction of existing pores. Changes in the porosity of deformed samples are evidenced by helium pycnometer and microscopy analyses. Radon and thoron exhalation rates are measured on groups of two samples by alpha spectrometer technique. Results show that tuff samples are characterised by a dual porosity consisting of a macroporosity, given by isolated large pores with sizes from mm‐ up to cm‐scale and a microporosity ranging between microns to hundreds of microns. At the end of the elastic phase pervasive pore collapse is observed, due to the closure of the cm‐scale macropores. This is mirrored by a significant decrease of radon and thoron release. After failure, a further reduction of porosity in the rock adjacent to the fault planes is observed due to extensive closure of both macropores and micropores. At this stage radon and thoron emissions increase. The formation of new exhaling surfaces is the main carrier of the bulk increase of radon and thoron exhalations, strongly prevailing over the densification carried out from the compaction mechanisms. In terms of volcanic hazard, negative anomalies in radon emissions should be considered as indicators of forthcoming ruptures. Key words: radon and thoron exhalation, tuff deformation, seismic precursor.
    Description: Published
    Description: L05305
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: Radon ; Rock deformation ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
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  • 58
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    Seismoacoustic investigations of paroxysmal activity at Mt. Etna volcano: New insights into the 16 November 2006 eruption (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On 16 November 2006, a 1 day long paroxysmal eruption occurred at the summit craters of Mt. Etna volcano. A multiparametric approach, consisting of analyzing infrasonic, seismic, and video camera recordings, was carried out to follow its evolution. Volcanological and geophysical observations identified three eruptive phases. In the first phase, infrasonic and seismic characteristics reflected the highly explosive nature of the activity. Waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of Southeast Crater (SEC). During the second phase, results highlighted the decoupling between seismic and infrasonic sources, which was due to the decrease in explosive activity and the reactivation of effusive vents located south of Bocca Nuova and on the saddle between Bocca Nuova and SEC. The third phase was the most intense and was characterized by various volcanic phenomena (pyroclastic flows, jets of dark ash, and white steam). The very high radiated infrasonic energy, together with infrasound event features, led us to infer a gas enrichment of the shallow magma column, preceding by a few minutes and likely related to the pyroclastic flows in the SEC area. After the eruption at SEC, variations in infrasound events related to the activity of Northeast Crater (NEC) were found. The observed spectral changes and the source mechanism modeling of the NEC infrasound events suggest the existence of a link in the plumbing system feeding the two craters.
    Description: Published
    Description: B09301
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Etna ; Infrasound ; volcanic tremor ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 59
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    FORMOSAT-3/COSMIC E region observations and daytime foE at middle latitudes (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Ionosonde observations at Rome and Gibilmanna (Sicily) for some months of 2006–2007 were analyzed in the connection with recent COSMIC NmE results. Italy was completely located in the NmE enhanced zone according to COSMIC observations for the periods in question. COSMIC‐observed NmE values in the NmE enhanced zone do not coincide with NmE scaled from ionograms in accordance with the URSI Recommendations, but the IRI model correctly describes monthly median NmE contrary to the Chu et al. (2009) conclusion. Three month averaged COSMIC NmE values turn out to be close to monthly median NmE corresponding to the blanketing frequency fbEs. A conclusion is made that sporadic E practically permanently existing during daytime hours in summer strongly contributes to NmE observed by COSMIC. Possible reasons for the occurrence of the NmE enhanced zones at middle latitudes are discussed.
    Description: Published
    Description: A06307
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: JCR Journal
    Description: restricted
    Keywords: mid-latitude ionosphere ; sporadic E layer ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 01. Atmosphere::01.02. Ionosphere::01.02.02. Dynamics
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  • 60
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    The initial phases of the 2008–2009 Mount Etna eruption: A multidisciplinary approach for hazard assessment (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Between 2007 and early 2008, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) monitoring networks on Etna volcano recorded a recharging phase that climaxed with a new effusive eruption on 13 May 2008 and lasted about 14 months. A dike‐forming intrusion was accompanied by a violent seismic swarm, with more than 230 events recorded in the first 6 h, the largest being ML = 3.9. In the meanwhile, marked ground deformation was recorded by the permanent tilt and GPS networks, and sudden changes in the summit area were detected by five continuously recording magnetic stations. Poor weather conditions did not allow direct observation of the eruptive events, but important information was provided by infrared satellite images that detected the start of lava fountains from the eruptive fissure, feeding a lava flow. This flow spread within the Valle del Bove depression, covering 6.4 km on the southeastern flank of the volcano in a few hours. The seismicity and deformation pattern indicated that the dike‐forming intrusion was propagating northward. It produced a dry fracture field, which generated concern for the possibility that the eruptive fissures could expand downslope toward populated areas. Monitoring and modeling of the multidisciplinary data, together with the simulations of ash dispersal and lava flows, allowed us both to infer the eruptive mechanisms and to provide correct interpretation of the ongoing phenomena, furnishing useful information for civil defense purposes. We describe how this approach of feedback between monitoring and research provides critical support to risk evaluation.
    Description: We wish to thank all our colleagues from INGV Sezione di Catania for data collection, for the maintenance of the monitoring networks during the whole eruption, and for the many discussions about the interpretation of the eruptive events; the Etna Guides, the Funivia dell’Etna, and especially Alfio Mazzaglia and Nino Mazzaglia for the prompt information pertaining any news about the summit eruptive activity at Mount Etna; the Italian Civil Defense (DPC) for the close and efficient collaboration built up during the last height years of activity at Etna and other Sicilian volcanoes. We obtained MODIS data from NASA and SEVIRI data from EUMETSAT. We are indebted to Paul Davis for his B03203 BONACCORSO ET AL.: ETNA MULTIDISCIPLINARY HAZARD ASSESSMENT B03203 17 of 19 positive and encouraging comments. We thank the Associate Editor Michael P. Ryan, who helped greatly in improving the form of the manuscript. This study was undertaken with partial financial support from the INGV‐DPC 2007–2009 Agreement. Scientific papers funded by DPC do not represent its official opinion and politics. We thank Stephen Conway for revising the English language of this manuscript.
    Description: Published
    Description: B03203
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: Etna ; effusive eruption ; hazard evaluation ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 61
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    Seismovolcanic signals at Deception Island volcano,Antarctica: Wave field analysis and source modeling (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-11-17
    Description: Island (Antarctica), recorded during three Antarctic summers (1994- 1995, 1995-1996 and 1996-1997), are analyzed using a dense small-aperture (500 m) seismic array. The visual and spectral classification of the seismic events shows the existence of long-period and hybrid isolated seismic events, and of low-frequency, quasi-monochromatic and spasmodic continuous tremors, All spectra have the highest amplitudes in the frequency band between 1 and 4 Hz, while hybrids and spasmodic tremors have also significant amplitudes in the high-frequency band (4-10 Hz). The array analysis indicates that almost all the well-correlated low-frequency signals share similar array parameters (slowness and back azimuth) and have the same source area, close to the array site. The polarization analysis shows that phases at high-frequency are mostly composed of P waves, and those phases dominated by low frequencies can be interpreted as surface waves. No clear shear waves are evidenced. From the energy evaluation, we have found that the reduced displacement values for surface and body waves are confined in a narrow interval. Volcano-tectonic seismicity is located close to the array, at a depth shallower than 1 km. The wave-field properties of the seismovolcanic signals allow us to assume a unique source model, a shallow resonating fluid-filled crack system at a depth of some hundreds of meters. All of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process. The differences observed in the back azimuth between low and high frequencies are a near-field effect. A few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe.
    Description: Published
    Description: 13905-13931
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Long Period Events ; Deception Island ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 62
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    A Holocene paleosecular variation record from the northwestern Barents Sea continental margin (2011)
    American Geophysical Union
    Details
    Publication Date: 2019-06-17
    Description: A high‐resolution paleomagnetic and rock magnetic study has been carried out on sediment cores collected in glaciomarine silty‐clay sequences from the continental shelf and slope of the southern Storfjorden trough‐mouth fan, on the northwestern Barents Sea continental margin. The Storfjorden sedimentary system was investigated during the SVAIS and EGLACOM cruises, when 10 gravity cores, with a variable length from 1.03 m to 6.41 m, were retrieved. Accelerator mass spectrometry (AMS) 14C analyses on 24 samples indicate that the cores span a time interval that includes the Holocene, the last deglaciation phase and in some cores the last glacial maximum. The sediments carry a well‐defined characteristic remanent magnetization and have a valuable potential to reconstruct the paleosecular variation (PSV) of the geomagnetic field, including relative paleointensity (RPI) variations. The paleomagnetic data allow reconstruction of past dynamics and amplitude of the geomagnetic field variations at high northern latitudes (75°–76° N). At the same time, the rock magnetic and paleomagnetic data allow a high‐resolution correlation of the sedimentary sequences and a refinement of their preliminary age models. The Holocene PSV and RPI records appear particularly sound, since they are consistent between cores and they can be correlated to the closest regional stacking curves (UK PSV, FENNOSTACK and FENNORPIS) and global geomagnetic model for the last 7 ka (CALS7k.2). The computed amplitude of secular variation is lower than that outlined by some geomagnetic field models, suggesting that it has been almost independent from latitude during the Holocene.
    Description: Published
    Description: Q11Z33
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Barents Sea ; Holocene ; Storfjorden ; geomagnetic paleosecular variation ; relative paleointensity ; 04. Solid Earth::04.05. Geomagnetism::04.05.01. Dynamo theory ; 04. Solid Earth::04.05. Geomagnetism::04.05.02. Geomagnetic field variations and reversals ; 04. Solid Earth::04.05. Geomagnetism::04.05.05. Main geomagnetic field ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
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  • 63
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    Laboratory measurements of the frictional properties of the Zuccale low-angle normal fault, Elba Island, Italy (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Using a case study from the island of Elba, Italy, we seek to test the hypothesis that the presence of minerals with low frictional strengths can explain prolonged slip on low-angle normal faults. The central core of the Zuccale low-angle normal fault contains a distinctive fault rock zonation that developed during progressive exhumation. Most fault rock components preserve microstructural evidence for having accommodated deformation entirely, or partly, by frictional mechanisms. One millimeter thick sample powders of all the major fault rock components were deformed in a triaxial deformation apparatus under water-saturated conditions, at room temperature, and at constant effective normal stresses of 25, 50, and 75 MPa. Pore fluid pressure was maintained at 50 MPa throughout. Overall, the coefficient of friction (m) of the fault rocks varies between 0.25 and 0.8, emphasizing the marked strength heterogeneity that may exist within natural fault zones. Also, m is strongly dependent on fault rock mineralogy and is 〈0.45 for fault rocks containing talc, chlorite, and kaolinite and 〉0.6 for fault rocks dominated by quartz, dolomite, calcite, and amphibole. Localization of frictional slip within talc-rich portions of the fault core can potentially explain movements along the Zuccale fault over a wide range of depths within the upper crust, although the mechanical importance of the talc-bearing fault rocks likely decreased following their dismemberment into a series of poorly connected fault rock lenses. Additionally, slip within clay-bearing fault gouges with m between 0.4 and 0.5 may have facilitated movements in the uppermost (〈2 km) crust. For several other fault rock components, m varies between 0.5 and 0.8, and mineralogical weakening alone is insufficient to account for low-angle slip. In the latter fault rock components, other weakening mechanisms such as the development of high fluid pressures, or dissolution-precipitation creep, may have been particularly important in reducing fault strength.
    Description: Published
    Description: B02407
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: Friction ; Low-Angle Normal Fault ; Elba ; Zuccale Fault ; Microstructure ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
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  • 64
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    A completeness analysis of the national seismic network of Italy (2010)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: We present the first detailed study of earthquake detection capabilities of the Italian National Seismic Network and of the completeness threshold of its earthquake catalog. The network in its present form started operating on 16 April 2005 and is a significant improvement over the previous networks. For our analysis, we employed the PMC method as introduced by Schorlemmer and Woessner (2008). This method does not estimate completeness from earthquakes samples as traditional methods, mostly based on the linearity of earthquake-size distributions. It derives detection capabilities for each station of the network and synthesizes them into maps of detection probabilities for earthquakes of a given magnitude. Thus, this method avoids the many assumptions about earthquake distributions that traditional methods make. The results show that the Italian National Seismic Network is complete at M=2.9 for the entire territory excluding the islands of Sardinia, Pantelleria, and Lampedusa. At the M=2.5 level, which is the reporting threshold level of the Italian Civil Protection, the network may miss events in southern parts of Apulia and the western part of Sicily. The stations are connected through many different telemetry links to the operational datacenter in Rome. Scenario computations show that no significant drop in completeness occurs if one of the three major links fail, indicating a well-balanced network setup.
    Description: Published
    Description: B04308
    Description: 5.2. TTC - Banche dati di sismologia strumentale
    Description: JCR Journal
    Description: open
    Keywords: Completeness Analysis ; Italian Seismicity ; Minimum Magnitude of Completeness ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
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  • 65
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    Increase in radon emission due to rock failure: An experimental study (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-02-24
    Description: Radon anomalies are commonly observed prior to dynamic failure in the crust and are interpreted as cracking of the medium, thus attracting considerable attention in understanding the precursory phenomena of earthquakes and volcanic activity. In this study we have compared the starting radon emissions from low porosity crystalline lava (phonolite) samples with those from damaged and failed samples. The damaged sample was loaded up to just beyond the end of the linear elastic phase, as evidenced by the output of AE energy, the increase in total porosity and a decrease in P‐wave and S‐wave velocity relative to the intact sample. Whereas, the failed sample showed deformation behaviour characteristically brittle with increasing values of AE output and porosity as the sample approached macroscopic failure. Radon measurements have evidenced that dilatational microcracking of deformed sample produced no significant variation in radon emanation with respect to the intact sample. In contrast, after macroscopic failure, radon emanation drastically increased. Therefore, major finding from this study is that, in the case of low porosity and relatively high strength crystalline lavas, the development of a macroscopic fracture provides new large exhaling surface resulting in a substantial increase in radon emission rate.
    Description: Published
    Description: L14304
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: Radon ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
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  • 66
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    Short‐term and long‐term tremor migration patterns of the Cascadia 2004 tremor and slow slip episode using small aperture seismic arrays (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union.
    Description: Tectonic tremor has been recorded at many subduction zones, including the Nankai, Cascadia, Mexican, and Alaskan subduction zones. This study, the first to use small aperture seismic arrays to track tremor, deployed three small aperture seismic arrays along the Cascadia subduction zone during a tremor and slow slip episode in July 2004. The tremor was active during virtually all (up to 99%) minutes of the analyzed tremor episode using 5 min sample windows. Individual wave phases were tracked across the arrays and used to derive slowness vectors. These were compared with slowness vectors computed from a standard layered Earth model to derive tremor locations. Locations were stable within a volume roughly 250 km2 in epicenter and 20 km in depth for hours to days before moving to a new volume. The migration between volumes was not smooth, and the movement of the sources within the volume followed no specific pattern. Overall migration speeds along the strike of the subduction zone were between 5 and 15 km/d; smaller scale migration speeds between volumes reached speeds up to 2 km/min. Uncertainties in the best locations were 5 km in epicenter and 10 km in depth. For this data set and processing methodology, tremor does not locate predominately on the primary subduction interface. Our favored model for the generation of tectonic tremor signals is that the tremor is triggered by stress and fluid pressure changes caused by slow slip and is composed, at least in part, of low‐frequency earthquakes broadly distributed in location
    Description: Published
    Description: B00A24
    Description: 3.2. Tettonica attiva
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: tremor migration ; Cascadia 2004 ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics
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  • 67
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    Modeling Earth Dynamics: Complexity, Uncertainty, and Validation (2011)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: 28th IUGG Conference on Mathematical Geophysics; Pisa, Italy, 7–11 June 2010; The capabilities and limits of mathematical models applied to a variety of geophysical processes were discussed during the 28th international Conference on Mathematical Geophysics, held in Italy (see the conference Web site (http://cmg2010.pi.ingv.it), which includes abstracts). The conference was organized by the International Union of Geodesy and Geophysics (IUGG) Commission on Mathematical Geophysics (CMG) and the Istituto Nazionale di Geofisica e Vulcanologia and was cosponsored by the U.S. National Science Foundation. The meeting was attended by more than 160 researchers from 26 countries and was dedicated to the theme “Modelling Earth Dynamics: Complexity, Uncertainty, and Validation.” Many talks were dedicated to illustration of the complexities affecting geophysical processes. Novel applications of geophysical fluid dynamics were presented, with specific reference to volcanological and ­subsurface/surface flow processes. In most cases, investigations highlighted the need for multidimensional and multiphase flow models able to describe the nonlinear effects associated with the nonhomogeneous nature of the matter. Fluid dynamic models of atmospheric, oceanic, and environmental systems also illustrated the fundamental role of nonlinear couplings between the different subsystems. Similarly, solid Earth models have made it possible to obtain the first tomographies of the planet; to formulate nonlocal and dynamic damage models of rocks; to investigate statistically the triggering, clustering, and synchronization of faults; and to develop realistic simulators of the planetary dynamo, plate tectonics, and gravity and magnetic fields.
    Description: Published
    Description: 506
    Description: 3.6. Fisica del vulcanismo
    Description: N/A or not JCR
    Description: reserved
    Keywords: mathematical models ; geophysics ; uncertainty ; validation ; 05. General::05.01. Computational geophysics::05.01.99. General or miscellaneous ; 05. General::05.05. Mathematical geophysics::05.05.99. General or miscellaneous
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  • 68
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    Tectonic evidence for the ongoing Africa-Eurasia convergence in central Mediterranean foreland areas: A journey among long-lived shear zones, large earthquakes, and elusive fault motions. (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An edited version of this paper was published by AGU. Copyright (2010) American Geophysical Union
    Description: We investigate the role of the Africa-Eurasia convergence in the recent tectonic evolution of the central Mediterranean. To this end we focused on two sectors of the Adriatic-Hyblean foreland of the Apennine-Maghrebian chain as they allow tectonic evidence for relative plate motions to be analyzed aside from the masking effect of other more local tectonic phenomena (e.g., subduction, chain building, etc.). We present a thorough review of data and interpretations on two major shear zones cutting these foreland sectors: the E-W Molise-Gondola in central Adriatic and the N-S Vizzini-Scicli in southern Sicily. The selected foreland areas exhibit remarkable similarities, including an unexpectedly high level of seismicity and the presence of the investigated shear zones since the Mesozoic. We analyze the tectonic framework, active tectonics, and seismicity of each of the foreland areas, highlighting the evolution of the tectonic understanding. In both areas, we find that current strains at midcrustal levels seem to respond to the same far-field force oriented NNW-SSE to NW-SE, similar to the orientation of the Africa-Eurasia convergence. We conclude that this convergence plays a primary role in the seismotectonics of the central Mediterranean and is partly accommodated by the reactivation of large Mesozoic shear zones.
    Description: The work has been funded by project “Sviluppo Nuove Tecnologie per la Protezione e Difesa del Territorio dai Rischi Naturali,” by the Italian Ministry of Education and Research (MIUR), and by the Italian Presidenza del Consiglio dei Ministri – Dipartimento della Protezione Civile (DPC).
    Description: Published
    Description: B12404
    Description: 3.2. Tettonica attiva
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: partially_open
    Keywords: Molise-Gondola shear zone ; Vizzini-Scicli shear zone ; Gargano Promontory ; Hyblean Plateau ; slip reversal ; 1627 earthquake ; 1693 earthquake ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Remote sensing for monitoring of land surface hydrology at high latitudes within the framework of the ESA DUE Permafrost and STSE ALANIS-Methane projects (GC41C-0820 Poster) (2011)
    American Geophysical Union
    In:  EPIC32011 AGU Fall Meeting, San Francisco, USA, 2011-12-05-2011-12-09San Francisco, American Geophysical Union
    Details
    Publication Date: 2019-07-17
    Description: Time series of a wide range of biogeophysical parameters from satellite data are available to date on a global scale. A few initiatives focus on their improvement and validation in high latitudes. For example the DUE Permafrost and STSE ALANIS-Methane, which are activities funded by the European Space Agency, focus on this issue. ALANIS Methane is a research project to produce and use a suite of relevant earth observation (EO) derived information to validate and improve one of the next generation land-surface models and thus reduce current uncertainties in wetland-related CH4 emissions. The task of the ESA DUE Permafrost project is to build up an Earth observation service for high-latitudinal permafrost applications. Results which are shown in this paper contribute to both. Microwave sensors are of special interest in this context due to their independence on cloud conditions and illumination of the Earth Surface. They can be used for derivation of land surface temperature, snow properties and land surface hydrology. The latter includes near surface soil moisture and inundation. Such parameters are of importance for studies on e.g. permafrost and land-atmosphere exchange. Datasets derived from active microwave instruments operating in C-band have been analysed with respect to their usability at high latitudes. Several examples from western Siberia are discussed.
    Repository Name: EPIC Alfred Wegener Institut
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    ESA DUE PERMAFROST: Remote Sensing Service for Permafrost - Adaption for Models (GC41B-0798 Poster) (2011)
    American Geophysical Union
    In:  EPIC32011 AGU Fall Meeting, San Francisco, USA, 2011-12-05-2011-12-09San Francisco, USA, American Geophysical Union
    Details
    Publication Date: 2019-07-16
    Description: The ESA DUE Permafrost project (2009-2011) is developing a suite of parameters indicative of the subsurface phenomenon permafrost using satellite remote sensing: Land Surface Temperature (LST), Surface Soil Moisture (SSM), Surface Frozen and Thawed State (Freeze/Thaw), Terrain, Land Cover (LC), and Surface Water (SW). Snow parameters (Snow Extent and Snow Water Equivalent) are being developed through the DUE GlobSnow project, Global Snow Monitoring for Climate Research (2008-2011). The final DUE Permafrost remote sensing products cover the years 2007 to 2011 with a circumpolar coverage that will soon be released (early 2012), and then be used to analyze the temporal dynamics and map the spatial patterns of indicators. Further information is available at www.ipf.tuwien.ac.at/ permafrost. Since the beginning, scientific stakeholders and the International Permafrost Association (IPA) have been involved in the science and implementation plan. Interactive international user workshops took place in 2010 at the Technical University of Vienna, Vienna (AT), and in 2011 at the International Arctic Research Center (IARC), Fairbanks, Alaska (US). This involvement and the ongoing evaluation of the indicators derived from remote sensing for the high-latitude permafrost regions make the DUE Permafrost products trustworthy for the permafrost and the climate research community. The adaption of the remote sensing products for the permafrost and climate modelling is experimental and highly dependent on the users’ involvement. For a few years already, the Geophysical Institute Permafrost Laboratory (GIPL), University of Alaska Fairbanks, US, (http://www.gi.alaska.edu/research/snowicepermafrost/Permafrost) has successfully demonstrated the value of using LST derived from remote sensing data for driving its permafrost models. Further experimental testing of the DUE Permafrost products for use by the modeling community (permafrost and climate) will range from (i) the evaluation of external data of the models, with modifying or providing new external data (e.g. tundra land cover, surface water ratio, soil distribution), to (ii) new drivers for regional models derived from remote sensing (e.g., LST), to (iii) the evaluation of the output data from the models (e.g. spatial patterns of moisture and temperature).
    Repository Name: EPIC Alfred Wegener Institut
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    ESA DUE Permafrost: Evaluation of remote sensing derived products using ground data from the Global Terrestrial Network of Permafrost (GTN-P) (2011)
    American Geophysical Union
    In:  EPIC3AGU 2011 Fall Meeting, San Francisco, 2011-12-05-2011-12-09SanFrancisco, American Geophysical Union
    Details
    Publication Date: 2019-07-16
    Description: The task of the ESA DUE Permafrost project is to build up an Earth observation service for high-latitudinal permafrost applications with extensive involvement of the permafrost research community. The DUE Permafrost products derived from remote sensing are land surface temperature (LST), surface soil moisture (SSM), surface frozen and thawed state (freeze/ thaw), terrain, land cover, and surface waters. Weekly and monthly averages for most of the DUE Permafrost products will be made available for the years 2007-2010. The DUE Permafrost products are provided for the circumpolar permafrost area (north of 55°N) with 25 km spatial resolution. In addition, regional products with higher spatial resolution (300-1000 m/ pixel) were developed for five case study regions. These regions are: (1) the Laptev Sea and Eastern Siberian Sea Region (RU, continuous very cold permafrost/ tundra), (2) the Yakutsk Region (RU, continuous cold permafrost/ taiga), (3) the Western Siberian transect including Yamal Peninsula and Ob Region (RU, continuous to discontinuous/ taiga-tundra), (4) the Alaska Highway Transect (US, continuous to discontinuous/ taiga-tundra), and (5) the Mackenzie Delta and Valley Transect (CA, continuous to discontinuous/ taiga-tundra). The challenge of the programme is to adapt remote sensing products that are well established and tested in agricultural low and mid-latitudinal areas for highly heterogeneous taiga/ tundra permafrost landscapes in arctic regions. Ground data is essential for the evaluation of DUE Permafrost products and is provided by user groups and global networks. A major part of the DUE Permafrost core user group is contributing to GTN-P, the Global Terrestrial Network of Permafrost. Its main programmes, the Circumpolar Active Layer Monitoring (CALM) and the Thermal State of Permafrost (TSP) have been thoroughly overhauled during the last International Polar Year (2007-2008). Their spatial coverage has been extended to provide a true circumpolar network. Ground data ranges from active layer- and snow depths, to air-, ground-, and borehole temperature data as well as soil moisture measurements and the description of landform and vegetation. The GTN-P sites, with their position in different permafrost zones in the DUE Permafrost case study regions, are highly suitable for the evaluation of DUE Permafrost remote sensing products. Air and surface temperatures with high-temporal resolution are available for three GTN-P sites in Siberia and compared to LST products. Daily average GTN-P borehole- and air temperature data for 22 sites in Alaska and 6 sites in Western Siberia were used to validate surface frozen and thawed state. The preliminary results are promising. In addition, landform and vegetation descriptions of circumpolar GTN-P sites are used for the evaluation of global ‘landcover’ remote-sensing datasets like GlobeCover, Landcover2000 and EcoClimap – global datasets used as input for climate modeling.
    Repository Name: EPIC Alfred Wegener Institut
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  • 72
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    Use of SF5CF3 for ocean tracer release experiments (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L04602, doi:10.1029/2007GL032799.
    Description: SF6 tracer release experiments (TREs) have provided fundamental insights in many areas of Oceanography. Recently, SF6 has emerged as a powerful transient tracer, generating a need for an alternative tracer for large-scale ocean TREs. SF5CF3 has the potential to replace SF6 in TREs, due to similarities in their properties and behavior, as well as techniques for injection, sampling, and analysis. The suitability of SF5CF3 for TREs was examined in Santa Monica Basin, off the coast of Southern California. In January 2005, a mixture of ca. 10 mol of both SF6 and SF5CF3 was injected on an isopycnal surface near 800 m depth. Over the next 23 months, concentrations of the two tracers mirrored each other very closely, indicating that SF5CF3 is a viable replacement for SF6 in ocean TREs. The mixing parameters inferred from the experiment confirmed the results from an earlier SF6 TRE in the Santa Monica Basin.
    Description: Funding was provided by the US National Science Foundation through OCE0425404 to W. Smethie and D. Ho and OCE0425197 to J. Ledwell.
    Keywords: Tracer release experiment ; 5-SF3-CF ; 6-SF
    Repository Name: Woods Hole Open Access Server
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  • 73
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    Variability in the Slope Water and its relation to the Gulf Stream path (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L03606, doi:10.1029/2007GL032183.
    Description: Sea Surface Temperature (SST) and Sea Surface Height (SSH) data for 1993–2007 for the North Atlantic are combined with hydrographic data at 69W to investigate the relation between the Gulf Stream (GS) position and the Slope Water properties. SST anomalies north of the GS are correlated with changes in its path. The lag of this correlation is such that positive temperature anomalies precede northward shifts of the GS, and suggests that SST anomalies move westward with speeds of several cm/s. EOF analysis of the SST and SSH fields shows that cooling and strengthening of the SW flow are in phase over the Slope Water, which is mirrored in the vertical structure of these fields at 69W, indicating larger transports in the Deep Western Boundary Current lead to southward shifts of the mean GS path. This relation between the Slope Water and the GS path provides some predictability for the latter.
    Keywords: Slope water ; Gulf Stream ; Variability
    Repository Name: Woods Hole Open Access Server
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  • 74
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    Wave dissipation by muddy seafloors (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L07611, doi:10.1029/2008GL033245.
    Description: Muddy seafloors cause tremendous dissipation of ocean waves. Here, observations and numerical simulations of waves propagating between 5- and 2-m water depths across the muddy Louisiana continental shelf are used to estimate a frequency- and depth-dependent dissipation rate function. Short-period sea (4 s) and swell (7 s) waves are shown to transfer energy to long-period (14 s) infragravity waves, where, in contrast with theories for fluid mud, the observed dissipation rates are highest. The nonlinear energy transfers are most rapid in shallow water, consistent with the unexpected strong increase of the dissipation rate with decreasing depth. These new results may explain why the southwest coast of India offers protection for fishing (and for the 15th century Portuguese fleet) only after large waves and strong currents at the start of the monsoon move nearshore mud banks from about 5- to 2-m water depth. When used with a numerical nonlinear wave model, the new dissipation rate function accurately simulates the large reduction in wave energy observed in the Gulf of Mexico.
    Description: The Office of Naval Research provided support.
    Keywords: Wave dissipation ; Muddy seafloor ; Coastal processes
    Repository Name: Woods Hole Open Access Server
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  • 75
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    Lability of DOC transported by Alaskan rivers to the Arctic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L03402, doi:10.1029/2007GL032837.
    Description: Arctic rivers transport huge quantities of dissolved organic carbon (DOC) to the Arctic Ocean. The prevailing paradigm is that DOC in arctic rivers is refractory and therefore of little significance for the biogeochemistry of the Arctic Ocean. We show that there is substantial seasonal variability in the lability of DOC transported by Alaskan rivers to the Arctic Ocean: little DOC is lost during incubations of samples collected during summer, but substantial losses (20–40%) occur during incubations of samples collected during the spring freshet when the majority of the annual DOC flux occurs. We speculate that restricting sampling to summer may have biased past studies. If so, then fluvial inputs of DOC to the Arctic Ocean may have a much larger influence on coastal ocean biogeochemistry than previously realized, and reconsideration of the role of terrigenous DOC on carbon, microbial, and food-web dynamics on the arctic shelf will be warranted.
    Description: This material is based on work supported by the National Science Foundation under grant numbers OPP-0436106, OPP- 0519840, and EAR-0403962, and is a contribution to the Study of Environmental Arctic Change (SEARCH).
    Keywords: DOC ; Arctic ; Rivers
    Repository Name: Woods Hole Open Access Server
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    Mixing across the Arctic Ocean : microstructure observations during the Beringia 2005 Expedition (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L08606, doi:10.1029/2008GL033532.
    Description: Turbulent-scale temperature and conductivity were measured during the pan-arctic Beringia 2005 Expedition. The rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from Alaska to the North Pole, across deep flat basins (Canada and Makarov Basins) and steep ridges (Alpha-Mendeleev and Lomonosov Ridges). The mixing rates are observed to be small relative to lower latitudes but also remarkably non-uniform. Relatively elevated turbulence is found over deep topography, confirming the dominant role of bottom-generated internal waves. Measured patterns of mixing in the Arctic are also associated with other mechanisms, such as double-diffusive structures and deep overflows. A better knowledge of the distribution of mixing is essential to understand the dynamics of the changing Arctic environment.
    Description: This work was funded by the National Science Foundation through a Small Grant for Exploratory Research (ARC-0527874) and grant ARC-0612342 with additional support from the Doherty Foundation and internal WHOI Funds.
    Keywords: Turbulence ; Arctic ; Topography
    Repository Name: Woods Hole Open Access Server
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    On the incompleteness of the historical record of North Atlantic tropical cyclones (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L11803, doi:10.1029/2008GL033546.
    Description: There is some question as to whether the historical record of observed North Atlantic tropical cyclones prior to the advent of satellite coverage is complete. This question is central to understanding the historical trend in tropical cyclone activity and the effect of environmental factors on it. To address this question, a statistical model of the relationship between annual cyclone counts between 1870 and 2004 and sea surface temperature and the state of the Southern Oscillation is extended to allow for non-decreasing observation probability prior to 1966. The estimated observation probabilities increase from 0.72 in 1870 to 1 in 1964. Allowing for record incompleteness reduces the estimated effect of sea surface temperature on annual tropical cyclone activity.
    Description: This work was supported by NOAA Grant NA17RJ1223.
    Keywords: Poisson regression model ; Observation probability ; North Atlantic tropical cyclones
    Repository Name: Woods Hole Open Access Server
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    Sea ice drift in the Arctic since the 1950s (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L19704, doi:10.1029/2008GL034791.
    Description: Sea ice drift data (from Russian North Pole stations, various ice camps, and the International Arctic Buoy Program) and surface wind stress data from the NCAR/NCEP Reanalysis are analyzed to determine their long-term trends and causality. The study finds that both parameters (ice drift and wind stress) show gradual acceleration over last 50 years. Significant positive trends are present in both winter and summer data. The major cause of observed positive trends is increasing Arctic storm activity over the Transpolar Drift Stream caused by a shift of storm tracks toward higher latitudes. It is speculated, with some observational evidence, that the increased stirring of the ocean by winds could hasten the transition of the Arctic toward a weakly stratified ocean with a potential for deep convection and a new sink for atmospheric CO2.
    Description: We are grateful for funding from the NASA Headquarters, NSF and IARC.
    Keywords: Climate variability ; Arctic and Antarctic oceanography ; Ice mechanics and air/sea/ice exchange processes
    Repository Name: Woods Hole Open Access Server
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    A comparison of in situ bottom pressure array measurements with GRACE estimates in the Kuroshio Extension (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L17601, doi:10.1029/2008GL034778.
    Description: Ocean bottom pressure estimates from Gravity Recovery and Climate Experiment (GRACE) have been validated by comparisons with an array of in situ bottom pressure measurements. The 600 km by 600 km array comprised 46 bottom pressure sensors that were part of the Kuroshio Extension System Study (KESS). Validations in other ocean regions have been limited by available data to pointwise bottom pressure measurements. Spatially-averaged monthly-mean bottom pressure over the KESS array is highly correlated with GRACE bottom pressure estimated at the center of the array. The correlations are nearly equally high for three standard choices of spatial smoothing radius applied to GRACE estimates, 300, 500, and 750 km. In contrast, pointwise comparisons between GRACE and individual bottom pressures are high or low in sub-regions of KESS, depending partially upon the local variance of deep mesoscale eddies whose energetic length scales are shorter than 300 km. KESS is a suitable validation experiment for the GRACE estimates at monthly scales with 300 to 750 km spatial radius of smoothing.
    Description: This work was supported by NSF grant OCE-0221008.
    Keywords: Ocean bottom pressure ; GRACE ; Kuroshio Extension
    Repository Name: Woods Hole Open Access Server
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  • 80
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    Low-frequency interaction between horizontal and overturning gyres in the ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L18614, doi:10.1029/2008GL035206.
    Description: Low-frequency variability of the horizontal circulation in an idealized, eddy-permitting, numerical model drives the dominant mode of low-frequency variability in the meridional overturning circulation. This coupling takes place through the influence of lateral advection in the cyclonic high-latitude boundary current on the mixed layer depth along the boundary. The mean and low-frequency variability of the meridional overturning circulation are well predicted by a diagnostic estimate that assumes the downwelling is controlled by the thermal wind shear within the mixed layer along the boundary, which is in turn determined by a simple balance between lateral advection and surface cooling. The more general result is the demonstration that the mean and low frequency variability of the meridional overturning streamfunction are controlled by the baroclinic pressure gradient within the mixed layer along the boundary, which may be influenced by numerous factors such as low-frequency variability in lateral advection, wind stress, surface buoyancy fluxes, or ice melt and freshwater runoff.
    Description: This work was supported by NSF grants OCE-0423975 and OCE-0726339.
    Keywords: Thermohaline circulation ; Climate variability
    Repository Name: Woods Hole Open Access Server
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    A nonparametric test for change in variability using a proxy record with an application to ENSO (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L19708, doi:10.1029/2008GL035400.
    Description: A common problem in climate science is determining whether the pattern of variability in a particular process or variable has changed over time. When the modern observational record is short, this problem can be addressed by comparing its variability to that of an historical proxy record. In doing so, it is important to recognize that the statistical properties of the modern and proxy records are different. Here, a nonparametric test for a change in variability in this situation is described that accounts for this difference. The method is illustrated by testing for a change in ENSO variability using a record of an ENSO index over the period 1871–2007 and oxygen isotope records extracted from corals at Palmyra Island that cover four different periods spanning the past millennium. The results are mixed.
    Description: Partial funding for this work was provided by NSF Grant DEB-0515639.
    Keywords: ENSO ; Proxy record
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    Significance of Langmuir circulation in upper ocean mixing : comparison of observations and simulations (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L10603, doi:10.1029/2009GL037620.
    Description: Representing upper ocean turbulence accurately in models remains a great challenge for improving weather and climate projections. Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum, heat, and mass in the oceanic surface layer. We present a direct comparison between observations and large eddy simulations, based on the wave-averaged Navier-Stokes equation, of an LC growth event. The evolution of cross-wind velocity variance and spatial scales, as well as mixed layer deepening are only consistent with simulations if LC effects are included in the model. Our results offer a validation of the large eddy simulation approach to understanding LC dynamics, and demonstrate the importance of LC in ocean surface layer mixing.
    Description: This research was supported by the Office of Naval Research through grants N00014-09-M-0112 (TK) and N00014-06-1-0178 (AP, JT). TK also received support from a Woods Hole Oceanographic Institution Cooperative Institute for Climate and Ocean Research Postdoctoral Scholarship.
    Keywords: Langmuir circulation
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    Reduced Antarctic meridional overturning circulation reaches the North Atlantic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L22601, doi:10.1029/2008GL035619.
    Description: We analyze abyssal temperature data in the western North Atlantic Ocean from the 1980s–2000s, showing that reductions in Antarctic Bottom Water (AABW) signatures have reached even that basin. Trans-basin oceanographic sections occupied along 52°W from 1983–2003 and 66°W from 1985–2003 quantify abyssal warming resulting from deepening of the strong thermal boundary between AABW and North Atlantic Deep Water (NADW), hence a local AABW volume reduction. Repeat section data taken from 1981–2004 along 24°N also show a reduced zonal gradient in abyssal temperatures, consistent with decreased northward transport of AABW. The reduction in the Antarctic limb of the MOC within the North Atlantic highlights the global reach of climate variability originating around Antarctica.
    Description: NOAA and NSF supported the 2003 U.S. CLIVAR/CO2 Repeat Hydrography Program reoccupations of the 52 W and 66 W sections, led by Chief Scientists John Toole and Terrence Joyce, respectively. The U.K. National Environment Research Council supported the 2004 reoccupation of the 24 N section, led by Chief Scientist Stuart Cunningham. The hard work of all contributing to the collection and processing of data analyzed here is gratefully acknowledged. The NOAA Office of Oceanic and Atmospheric Research and the NOAA Climate Program Office supported the analysis.
    Keywords: Antarctic bottom water ; Meridional overturning circulation
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    Flow-weighted values of runoff tracers (δ18O, DOC, Ba, alkalinity) from the six largest Arctic rivers (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L18606, doi:10.1029/2008GL035007.
    Description: We present new flow-weighted data for δ 18OH2O, dissolved organic carbon (DOC), dissolved barium and total alkalinity from the six largest Arctic rivers: the Ob', Yenisey, Lena, Kolyma, Yukon and Mackenzie. These data, which can be used to trace runoff, are based upon coordinated collections between 2003 and 2006 that were temporally distributed to capture linked seasonal dynamics of river flow and tracer values. Individual samples indicate significant variation in the contributions each river makes to the Arctic Ocean. Use of these new flow-weighted estimates should reduce uncertainties in the analysis of freshwater transport and fate in the upper Arctic Ocean, including the links to North Atlantic thermohaline circulation, as well as regional water mass analysis. Additional improvements should also be possible for assessing the mineralization rate of the globally significant flux of terrigenous DOC contributed to the Arctic Ocean by these major rivers.
    Description: Supported by the U.S. National Science Foundation (OPP-0229302), the U.S. Geological Survey and the Water Resources Division of Canada’s Department of Indian Affairs and Northern Development.
    Keywords: Arctic rivers ; Tracers
    Repository Name: Woods Hole Open Access Server
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    High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice cores (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L13501, doi:10.1029/2009GL037643.
    Description: Semi-volatile organic compounds derived from burned and fresh vascular plant sources and preserved in high-altitude ice fields were detected and identified through use of recently developed analytical tools. Specifically, stir bar sorptive extraction and thermal desorption coupled with gas chromatography/time-of-flight mass spectrometry allowed measurement of multiple biomarkers in small sample volumes (≤30 ml). Among other compounds of interest, several diterpenoids, which suggest inputs from conifers and conifer burning, were identified in post-industrial era and older Holocene ice from the Sajama site in the Bolivian Andes, but not in a glacial period sample, consistent with aridity changes. Differences in biomarker assemblages between sites support the use of these compounds as regionally constrained recorders of vegetation and climate change. This study represents the first application of these analytical techniques to ice core research and the first indication that records of vegetation fires may be reconstructed from diterpenoids in ice.
    Description: This project was supported in part by NSF-OCE (0402533), and NSF-EAR (0094475).
    Keywords: Biomass burning ; Molecular markers
    Repository Name: Woods Hole Open Access Server
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    The subtropical nutrient spiral (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 17 (2003): 1110, doi:10.1029/2003GB002085.
    Description: We present an extended series of observations and more comprehensive analysis of a tracer-based measure of new production in the Sargasso Sea near Bermuda using the 3He flux gauge technique. The estimated annually averaged nitrate flux of 0.84 ± 0.26 mol m−2 yr−1 constitutes only that nitrate physically transported to the euphotic zone, not nitrogen from biological sources (e.g., nitrogen fixation or zooplankton migration). We show that the flux estimate is quantitatively consistent with other observations, including decade timescale evolution of the 3H + 3He inventory in the main thermocline and export production estimates. However, we argue that the flux cannot be supplied in the long term by local diapycnal or isopycnal processes. These considerations lead us to propose a three-dimensional pathway whereby nutrients remineralized within the main thermocline are returned to the seasonally accessible layers within the subtropical gyre. We describe this mechanism, which we call “the nutrient spiral,” as a sequence of steps where (1) nutrient-rich thermocline waters are entrained into the Gulf Stream, (2) enhanced diapycnal mixing moves nutrients upward onto lighter densities, (3) detrainment and enhanced isopycnal mixing injects these waters into the seasonally accessible layer of the gyre recirculation region, and (4) the nutrients become available to biota via eddy heaving and wintertime convection. The spiral is closed when nutrients are utilized, exported, and then remineralized within the thermocline. We present evidence regarding the characteristics of the spiral and discuss some implications of its operation within the biogeochemical cycle of the subtropical ocean.
    Description: This work was supported by grants from the National Science Foundation (OCE-0221247) and NSF/ONR NOPP (N000140210370).
    Keywords: Nutrients ; Productivity ; Tritium ; Helium-3
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    Cobalt and nickel in the Peru upwelling region : a major flux of labile cobalt utilized as a micronutrient (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 18 (2004): GB4030, doi:10.1029/2003GB002216.
    Description: The geochemistry of cobalt in the Peru upwelling region is dominated by its importance as a micronutrient. A large and previously undocumented flux of labile cobalt behaved as a micronutrient with correlations with major nutrients (nitrate, phosphate; r 2 = 0.90, 0.96) until depleted to ≤50 pM of strongly complexed cobalt. Co:P utilization ratios were an order of magnitude higher than in the North Pacific, comparable to utilization rates of zinc in other oceanic regions. Cobalt speciation measurements showed that available cobalt decreased over 4 orders of magnitude in this region, with shifts in phytoplankton assemblages occurring at transitions between labile and nonlabile cobalt. Only small changes in total dissolved nickel were observed, and nickel was present in a labile chemical form throughout the region. In the Peru upwelling region, cobalt uptake was highest at the surface and decreased with depth, suggesting phytoplankton uptake was a more important removal mechanism than co-oxidation with microbial manganese oxidation. These findings show the importance of cobalt as a micronutrient and that cobalt scarcity and speciation may be important in influencing phytoplankton species composition in this economically important environment.
    Description: This work was supported by the NSF under grant OCE-9618729 and OCE-0327225.
    Keywords: Cobalt speciation ; Nickel ; Peru upwelling ; Pacific ; Phytoplankton
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    A three-dimensional, multinutrient, and size-structured ecosystem model for the North Atlantic (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 18 (2004): GB3019, doi:10.1029/2003GB002146.
    Description: We incorporate multinutrient and size-structured ecosystem dynamics into a three-dimensional ocean general circulation model for the North Atlantic. The model reproduces the magnitude and general spatial and temporal patterns in nutrients, chlorophyll and primary production seen in in situ (BATS, NABE, and OWSI) and satellite (SeaWiFS) data, showing substantial improvements over prior basin-scale simulations. Model skill is evaluated quantitatively against SeaWiFS data using a Taylor diagram approach. Model-data correlation R for the overall surface chlorophyll time-space distribution is ∼0.6, with comparable model and observed total variability. The agreement relative to satellite-based primary production is somewhat weaker (0.2 〈 R 〈 0.5). The simulations capture observed ecological characteristics, e.g., the dominance of picoplankton and episodic diatom blooms in the subtropics, nutrient-controlled plankton succession at higher latitudes, and associated seasonal/depth changes in new and regenerated production and particle export. In a sensitivity experiment that mimics behavior of simpler single-species models, removal of diatom silica limitation leads to major shifts in community structure and export and larger model-data errors similar to previous model studies. Model results also suggest that episodic diatom blooms at BATS may be related to interannual variations in the southward transport of nutrients, mainly SiO3, and plankton cells.
    Description: Support for this work was provided by NASA SeaWiFS grant W-19,223 and NSF JGOFS SMP grant 0222033.
    Keywords: Ecosystem model ; North Atlantic ; Multinutrient ; Size-structure ; Silica limitation
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    Organic matter in river-influenced continental margin sediments : the land-ocean and climate linkage at the Late Quaternary Congo fan (ODP Site 1075) (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 4 (2003): 1109, doi:10.1029/2003GC000590.
    Description: Late Quaternary sections (1.2 Ma) of ODP-Site 1075 from the Congo deep-sea fan are investigated to reconstruct variations of terrigenous organic matter supply to the eastern equatorial Atlantic. To characterize the organic matter (OM) with regard to marine and terrigenous amounts we used elemental analysis (C, N, S), stable carbon isotopes (bulk δ13Corg), Rock-Eval pyrolysis, and terrigenous biomarkers (lignin phenols from CuO oxidation). The records of total organic carbon (TOC) contents, Corg/Ntot ratios, bulk OM degradation rates (Corg/Corg*), and the ratios of hydrocarbons (HC) from low-mature versus HC from high-mature OM (lm/hm) reveal pronounced cyclic changes in OM abundance, preservation, and reactivity that are closely related to the precessional controlled record of insolation, and thus, to variations in upwelling intensity and fluvial run-off. Primary productivity off the Congo is stimulated by both, enhanced nutrient supply in response to trade-induced upwelling during arid African climates (insolation minima) and fluvial nutrient delivery during humid stages (following insolation maxima), especially due to the contribution of dissolved silica that is taken up preferably by diatoms. However, results stemming from a multiparameter approach reveal that the fluvial supply of degraded OM and black carbon (BC) associated with fine-grained sediments from soil erosion is a decisive factor for the preservation of marine OM and, in addition, significantly influences the geochemical signature of bulk and terrigenous OM. Riverine and eolian supply of C4 plant matter, as well as enhanced concentrations of BC, during arid and arid-to-humid transitional climate stages, may lead to a severe underestimation of terrigenous organic carbon, if its amount is calculated from bulk isotopic ratios using binary end-member models. During the humid stages, it is the massive supply of 13C-enriched soil OM with low Corg/Ntot ratios that may suggest a mainly marine composition of bulk OM. In fact, terrigenous OM governs bulk OM geochemical signatures in the sediments of the Congo deep-sea fan, a result that is contradictory to earlier studies, especially to the conventional interpretation of the bulk δ13Corg signal.
    Description: This research was funded by the Deutsche Forschungsgemeinschaft, grant Wa 1036/5, and kindly supported by the Max-Planck Society.
    Keywords: Congo deep-sea fan ; Terrestrial organic matter ; Lignin ; Organic matter reactivity ; Insolation forcing ; Quaternary tropical Atlantic
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    A record of eruption and intrusion at a fast spreading ridge axis : axial summit trough of the East Pacific Rise at 9–10°N (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q10T07, doi:10.1029/2008GC002354.
    Description: High-resolution side-scan sonar, near-bottom multibeam bathymetry, and deep-sea photo and bathymetry traverses are used to map the axial summit trough (AST) at the East Pacific Rise between 9 and 10°N. We define three ridge axis morphologic types: no AST, narrow AST, and wide AST, which characterize distinct ridge crest domains spanning tens of kilometers along strike. Near-bottom observations, modeling of deformation above intruding dikes, and comparisons to the geologic and geophysical structure of the ridge crest are used to develop a revised model of AST genesis and evolution. This model helps constrain the record of intrusive and extrusive magmatism and styles of lava deposition along the ridge crest at time scales from hundreds to tens of thousands of years. The grabens in the narrow-AST domain (9°43′–53′N) are consistent with deformation above the most recent (〈10) diking events beneath the ridge crest. Frequent high–effusion rate extrusive volcanism in this domain (several eruptions every ∼100 years) overprints near-axis deformation and maintains a consistent AST width. The most recent eruption at the ridge crest occurred in this area and did not significantly modify the physical characteristics of the AST. The grabens in the wide-AST domain (9°23′–43′N) originated with similar dimensions to the narrow AST. Spreading, driven primarily by the intrusion of shallow dikes within a narrow axial zone, causes the initial graben bounding faults to migrate away from the axis. Infrequent extrusive volcanism (several eruptions every ∼1000 years) fills a portion of the subsidence that accumulates over time but does not significantly modify the width of the AST. Outside of these domains, lower–effusion rate constructional volcanism without efficient drain-back fills and erases the signature of the AST. The relative frequency of intrusive versus extrusive magmatic events controls the morphology of the ridge crest and appears to remain constant over millennial time scales within the domains we have identified; however, over longer time scales (∼10–25 ka), domain-specific intrusive-to-extrusive ratios do not appear to be fixed in space, resulting in a fairly consistent volcanic accretion over the length scale of the second-order ridge segment between 9°N and 10°N.
    Description: This work was supported by NSF grants OCE-0525863 to D. Fornari and S. A. Soule; OCE-0732366 to S. A. Soule; and OCE-9819261 to H. Schouten, M. Tivey, and D. Fornari and by CNRS to J. Escartın.
    Keywords: Mid-ocean ridge ; Submarine volcanism ; Diking ; Seafloor morphology ; Magmatism
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    A new automated method for measuring noble gases and their isotopic ratios in water samples (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q05008, doi:10.1029/2009GC002429.
    Description: A method is presented for precisely measuring all five noble gases and their isotopic ratios in water samples using multiple programmed multistage cryogenic traps in conjunction with quadrupole mass spectrometry and magnetic sector mass spectrometry. Multiple automated cryogenic traps, including a two-stage cryotrap used for removal of water vapor, an activated charcoal cryotrap used for helium separation, and a stainless steel cryotrap used for neon, argon, krypton, and xenon separation, allow reproducible gas purification and separation. The precision of this method for gas standards is ±0.10% for He, ±0.14% for Ne, ±0.10% for Ar, ±0.14% for Kr, and ±0.17% for Xe. The precision of the isotopic ratios of the noble gases in gas standards are ±1.9‰ for 20Ne/22Ne, ±2.0‰ for 84Kr/86Kr, ±2.5‰ for 84Kr/82Kr, ±0.9‰ for 132Xe/129Xe, and ±1.3‰ for 132Xe/136Xe. The precision of this method for water samples, determined by measurement of duplicate pairs, is ±1% for He, ±0.9% for Ne, ±0.3% for Ar, ±0.3% for Kr, and ±0.2% for Xe. An attached magnetic sector mass spectrometer measures 3He/4He with precisions of ±0.1% for air standards and ±0.14% for water samples.
    Description: We are grateful for support by the National Science Foundation Chemical Oceanography program (OCE-0221247), by the Department of Defense (graduate fellowship to RHRS), and by the Woods Hole Oceanographic Institution (postdoctoral fellowship for B.B.).
    Keywords: Noble gas ; Oceanography ; Mass spectrometry ; Seawater ; Isotope ; Cryogenic
    Repository Name: Woods Hole Open Access Server
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    Halocline structure in the Canada Basin of the Arctic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2005. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 32 (2005): L03605, doi:10.1029/2004GL021358.
    Description: We examine the varieties and spatial distributions of Pacific and Eastern Arctic origin halocline waters in the Canada Basin using 2002–2003 hydrographic data. The halocline structure in the Canada Basin is different from the Eastern Arctic halocline because it includes fresher Pacific Winter Waters that form a “cold halostad” which lies above the Eastern Arctic origin lower halocline waters. The structure of the halostad in the Canada Basin, however, is not spatially uniform, and depends on the pathway and history of the source water. Pacific Winter Water entering through the Bering Strait becomes salty due to sea ice formation and this, in turn, is dependent on the occurrence and distribution of polynyas. In particular, saline water from the eastern Chukchi Sea forms thick halostad and causes depression of the isohalines in the southern Canada Basin. This depression influences thermohaline structure of the oceanic Beaufort Gyre.
    Description: This work was funded in part by the Japan Agency for Marine-Earth Science and Technology, the Fisheries and Oceans Canada, and the U.S. National Science Foundation.
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    A potential bias in coral reconstruction of sea surface temperature (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L06308, doi:10.1029/2003GL019349.
    Description: Isotopic measurements in corals are used to reconstruct past sea surface temperature. These reconstructions are based on calibration regression analyses using paired measurements of modern isotopic composition and sea surface temperature. It is shown that error in these measurements of sea surface temperature can lead to substantial bias in reconstruction. Provided the variance of the measurement error is known or can be estimated, a simple correction can eliminate this bias.
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    An interlaboratory study of TEX86 and BIT analysis using high-performance liquid chromatography–mass spectrometry (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q03012, doi:10.1029/2008GC002221.
    Description: Recently, two new proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) were proposed, i.e., the TEX86 proxy for sea surface temperature reconstructions and the BIT index for reconstructing soil organic matter input to the ocean. In this study, fifteen laboratories participated in a round robin study of two sediment extracts with a range of TEX86 and BIT values to test the analytical reproducibility and repeatability in analyzing these proxies. For TEX86 the repeatability, indicating intra-laboratory variation, was 0.028 and 0.017 for the two sediment extracts or ±1–2°C when translated to temperature. The reproducibility, indicating among-laboratory variation, of TEX86 measurements was substantially higher, i.e., 0.050 and 0.067 or ±3–4°C when translated to temperature. The latter values are higher than those obtained in round robin studies of Mg/Ca and U37 k′ paleothermometers, suggesting the need to primarily improve compatibility between labs. The repeatability of BIT measurements for the sediment with substantial amounts of soil organic matter input was relatively small, 0.029, but reproducibility was large, 0.410. This large variance could not be attributed to specific equipment used or a particular data treatment. We suggest that this may be caused by the large difference in the molecular weight in the GDGTs used in the BIT index, i.e., crenarchaeol versus the branched GDGTs. Potentially, this difference gives rise to variable responses in the different mass spectrometers used. Calibration using authentic standards is needed to establish compatibility between labs performing BIT measurements.
    Keywords: TEX86 ; BIT ; Round robin ; HPLC/MS
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    Coastal ocean wind fields gauged against the performance of an ocean circulation model (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L14303, doi:10.1029/2003GL019261.
    Description: Atmosphere model-derived flux fields are used to force coastal ocean models. Coarse resolution and incomplete boundary layer dynamics limit the accuracy of these forcing fields and hence the performance of the ocean models. We address this limitation for the west Florida shelf using optimal interpolation to blend winds measured in situ with winds produced by model analyses. By improving the coastal wind field we improve the fidelity between currents modeled and currents observed. Comparisons between momentum analyses performed independently from the model and the data demonstrate the fidelity to be of a correct dynamical basis. We conclude that the primary limitation to coastal ocean model performance lies with the boundary conditions.
    Description: Support was provided by the Office of Naval Research, Grant #s N00014-98-1-0158 and N00014-02-1-0972.
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    Tidal modulation of Sr/Ca ratios in a Pacific reef coral (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L16310, doi:10.1029/2004GL020600.
    Description: The strontium-to-calcium ratio (Sr/Ca) of reef coral skeleton is an important tool for reconstructing past sea surface temperatures (SSTs). However, the accuracy of paleoSSTs derived from fossil coral Sr/Ca is challenged by evidence that physiological processes influence skeletal chemistry. Here we show that water level variations from tidal forcing are correlated with changes in coral Sr/Ca that cannot be accounted for by changes in SST. Ion microprobe measurements of Sr/Ca ratios in a Pacific Porites lutea reveal high-frequency variations at periods of ~6, ~10, and ~25 days. The relationship between Sr/Ca and temperature on these short timescales does not follow trends observed at longer periods, indicating that an additional forcing is required to explain our observations. We demonstrate that Sr/Ca is correlated with both tidal water level variations and SST, and that their contributions to the Sr/Ca content of the skeleton vary as a function of period. We propose that water level influences Sr/Ca indirectly via modulation of photosynthetically-active radiation (PAR) that drives large changes in zooxanthellate photosynthesis.
    Description: This research was supported by WHOI Ocean Life Institute grant 25051316 to ALC; NSF grants EAR-9628749 and EAR-9904400 to the WHOI Northeast National Ion Microprobe Facility; DAMD 17-93-J-3052 supported ALC’s fieldwork on JA.
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    Observation of very large and steep internal waves of elevation near the Massachusetts coast (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L22307, doi:10.1029/2004GL021052.
    Description: We report on near-bottom waves of elevation with amplitude nearly half the 25 m water column, very steep, and propagating into a sheared turbulent wave-guide. The waves contained trapped cores transporting parcels of water shoreward. These large waves depart strongly from weakly-nonlinear and weakly-nonhydrostatic conditions and challenge established paradigms. They can also represent an important factor in the across-shore transport of plankton and contaminants.
    Description: Funding provided by ONR, grants N00014-01-1-0172 and N00014-03-1-0553.
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    Seismic reflection imaging of water mass boundaries in the Norwegian Sea (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L23311, doi:10.1029/2004GL021325.
    Description: Results from the first joint temperature and seismic reflection study of the ocean demonstrate that water mass boundaries can be acoustically mapped. Multichannel seismic profiles collected in the Norwegian Sea show reflections between the Norwegian Atlantic Current and Norwegian Sea Deep Water. The images were corroborated with a dense array of expendable bathythermographs and expendable conductivity-temperature depth profiles delineating sharp temperature gradients over vertical distances of ∼5–15 m at depths over which reflections occur. Fine structure from both thermohaline intrusions and internal wave strains is imaged. Low-amplitude acoustic reflections correspond to temperature changes as small as 0.03°C implying that seismic reflection methods can image even weak fine structure.
    Description: Supported by NSF grants OCE-0221366 and OCE-0337289 to Holbrook.
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    Unraveling the sequence of serpentinization reactions : petrography, mineral chemistry, and petrophysics of serpentinites from MAR 15°N (ODP Leg 209, Site 1274) (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L13306, doi:10.1029/2006GL025681.
    Description: The results of detailed textural, mineral chemical, and petrophysical studies shed new light on the poorly constrained fluid-rock reaction pathways during retrograde serpentinization at mid-ocean ridges. Uniformly depleted harzburgites and dunites from the Mid-Atlantic Ridge at 15°N show variable extents of static serpentinization. They reveal a simple sequence of reactions: serpentinization of olivine and development of a typical mesh texture with serpentine-brucite mesh rims, followed by replacement of olivine mesh centers by serpentine and brucite. The serpentine mesh rims on relic olivine are devoid of magnetite. Conversely, domains in the rock that are completely serpentinized show abundant magnetite. We propose that low-fluid-flux serpentinization of olivine to serpentine and ferroan brucite is followed by later stages of serpentinization under more open-system conditions and formation of magnetite by the breakdown of ferroan brucite. Modeling of this sequence of reactions can account for covariations in magnetic susceptibility and grain density of the rocks.
    Description: Funding for this research was provided by USSSP and NSF-OCE grant 9986135. WB acknowledges support through a fellowship by the Deep Ocean Exploration Institute.
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    Pacific Ocean inflow : influence on catastrophic reduction of sea ice cover in the Arctic Ocean (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 33 (2006): L08605, doi:10.1029/2005GL025624.
    Description: The spatial pattern of recent ice reduction in the Arctic Ocean is similar to the distribution of warm Pacific Summer Water (PSW) that interflows the upper portion of halocline in the southern Canada Basin. Increases in PSW temperature in the basin are also well-correlated with the onset of sea-ice reduction that began in the late 1990s. However, increases in PSW temperature in the basin do not correlate with the temperature of upstream source water in the northeastern Bering Sea, suggesting that there is another mechanism which controls these concurrent changes in ice cover and upper ocean temperature. We propose a feedback mechanism whereby the delayed sea-ice formation in early winter, which began in 1997/1998, reduced internal ice stresses and thus allowed a more efficient coupling of anticyclonic wind forcing to the upper ocean. This, in turn, increased the flux of warm PSW into the basin and caused the catastrophic changes.
    Description: This work was funded in part by Japan Agency for Marine-Earth Science and Technology, Fisheries and Oceans Canada, and the U.S. National Science Foundation.
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