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  • Institute of Physics  (48,948)
  • American Geophysical Union  (11,551)
  • Cell Press  (10,040)
  • Annual Reviews
  • 2005-2009  (71,707)
  • 1955-1959
  • 2007  (36,231)
  • 2006  (35,476)
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  • 2005-2009  (71,707)
  • 1955-1959
Year
  • 1
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    Coulomb stress changes caused by repeated normal faulting earthquakes during the 1997 Umbria-Marche (central Italy) seismic sequence (2007)
    American Geophysical Union
    Details
    Publication Date: 2021-01-05
    Description: We investigate fault interaction through elastic stress transfer among a sequence of moderate-magnitude main shocks (5 〈 Mw 〈 6) which ruptured distinct normal fault segments during a seismic sequence in the Umbria-Marche region (central Apennines). We also model the spatial pattern of aftershocks and their faulting mechanisms through Coulomb stress changes. We compute stress perturbations caused by earthquake dislocations in a homogeneous half-space. Our modeling results show that seven out of eight main shocks of the sequence occur in areas of enhanced Coulomb stress, implying that elastic stress transfer may have promoted the occurrence of these moderate- magnitude events. Our modeling results show that stress changes caused by normal faulting events reactivated and inverted the slip of a secondary N-S trending strike-slip fault inherited from compressional tectonics in its shallowest part (1–3 km). Of the 1517 available aftershocks, 82% are located in areas of positive stress changes for optimally oriented planes (OOPs) for Coulomb failure. However, only 45% of the 322 available fault plane solutions computed from polarity data is consistent with corresponding focal mechanisms associated with the OOPs. The comparison does not improve if we compute the optimally oriented planes for Coulomb failure by fixing the strike orientation of OOPs using information derived from structural geology. Our interpretation of these modeling results is that elastic stress transfer alone cannot jointly explain the aftershock spatial distribution and their focal mechanisms.
    Description: Published
    Description: B05S20
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Coulomb Stress Changes ; Normal Faulting ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 1. Flow direction and deposition (2007)
    American Geophysical Union
    Details
    Publication Date: 2021-06-15
    Description: To assess ways in which the products of explosive eruptions interact with human settlements, we performed volcanological and rock magnetic analyses on the deposits of the A.D. 79 eruption at the Pompeii excavations (Italy). During this eruption the Roman town of Pompeii was covered by 2.5 m of fallout pumice and then partially destroyed by pyroclastic density currents (PDCs). Anisotropy of magnetic susceptibility measurements performed on the fine matrix of the deposits allowed the quantification of the variations in flow direction and emplacement mechanisms of the parental PDCs that entered the town. These results, integrated with volcanological field investigations, revealed that the presence of buildings, still protruding through the fallout deposits, strongly affected the distribution and accumulation of the erupted products. All of the PDCs that entered the town, even the most dilute ones, were density stratified currents in which interaction with the urban fabric occurred in the lower part of the current. The degree of interaction varied mainly as a function of obstacle height and density stratification within the current. For examples, the lower part of the EU4pf current left deposits up to 3 m thick and was able to interact with 2- to 4-m-high obstacles. However, a decrease in thickness and grain size of the deposits across the town indicates that even though the upper portion of the current was able to decouple from the lower portion, enabling it to flow over the town, it was not able to fully restore the sediment supply to the lower portion in order to maintain the deposition observed upon entry into the town.
    Description: Published
    Description: B05213
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Pompeii ; facies ; magnetic fabric ; pyroclastic density currents ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 2. Temperature of the deposits and hazard implications (2007)
    American Geophysical Union
    Details
    Publication Date: 2021-06-15
    Description: During the A.D. 79 eruption of Vesuvius, Italy, the Roman town of Pompeii was covered by 2.5 m of pyroclastic fall pumice and then partially destroyed by pyroclastic density currents (PDCs). Thermal remanent magnetization measurements performed on the lithic and roof tile fragments embedded in the PDC deposits allow us to quantify the variations in the temperature (Tdep) of the deposits within and around Pompeii. These results reveal that the presence of buildings strongly influenced the deposition temperature of the erupted products. The first two currents, which entered Pompeii at a temperature around 300–360°C, show drastic decreases in the Tdep, with minima of 100–140°C, found in the deposits within the town. We interpret these decreases in temperature as being the result of localized interactions between the PDCs and the city structures, which were only able to affect the lower part of the currents. Down flow of Pompeii, the lowermost portion of the PDCs regained its original physical characteristics, emplacing hot deposits once more. The final, dilute PDCs entered a town that was already partially destroyed by the previous currents. These PDCs left thin ash deposits, which mantled the previous ones. The lack of interaction with the urban fabric is indicated by their uniform temperature everywhere. However, the relatively high temperature of the deposits, between 140 and 300°C, indicates that even these distal, thin ash layers, capped by their accretionary lapilli bed, were associated with PDCs that were still hot enough to cause problems for unsheltered people.
    Description: Published
    Description: B05214
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Pompeii ; temperature ; magnetic fabric ; pyroclastic density currents ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    Real-time measurement of volcanic H2S and SO2 concentrations by UV spectroscopy (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Sulphur speciation in volcanic gases acts as a major redox buffer, and H2S/SO2 ratios represent a valuable indicator of magmatic conditions and interactions between magmatic and hydrothermal fluids. However, measurement of H2S/SO2 even by direct sampling techniques, is not straightforward. We report here on application of a small ultraviolet spectrometer for real-time field measurement of H2S and SO2 concentrations, using open-path and extractive configurations. The device was tested at fumaroles on Solfatara and Vulcano, Italy, in November 2002. H2S concentrations of up to 220ppmm(400 ppmv) were measured directly above the Bocca Grande fumarole at Solfatara, and H2S/SO2 molar ratios of 2 and 2.4, respectively, were determined for the ‘F11’ and ‘F0’ fumaroles at Vulcano. In comparison with other optical techniques capable of multiple volcanic gas measurements, such as laser and FTIR spectroscopy, this approach is considerably simpler and cheaper, with the potential for autonomous, sustained hightime resolution operation.
    Description: Published
    Description: 1652
    Description: partially_open
    Keywords: Remote monitoring ; Plume chemistry ; sulphur species ; 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
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Lithospheric rheology in southern Italy inferred from postseismic viscoelastic relaxation following the 1980 Irpinia earthquake (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Postseismic relaxation is modeled for the Irpinia earthquake, which struck southern Italy in 1980. Our goal is to understand the mechanism of surface deformation due to stress relaxation in the deep portion of the crust-lithosphere system for a shallow normal fault source and to infer the rheological properties of the lithosphere in the extensional environment of peninsular Italy. The modeling is carried out within the framework of our normal mode viscoelastic theory at high spatial resolution in order to accurately resolve the vertical surface displacements for a seismic source. The slip distribution over the faults is first inverted from coseismic leveling data, the misfit between observed and modeled vertical displacements being minimized by means of the L2 norm. Slip distribution is then used within the viscoelastic model to invert for the viscosities of the lower crust and generally of the lithosphere. Inversion is based on leveling data sampled along three lines crossing the epicentral area. Postseismic deformation in the Irpinia area is characterized by a broad region of crust upwarping in the footwall of the major fault and downwarping in the hanging wall that is responsible for the long-wavelength features of the vertical displacement pattern. The c2 analysis indicates that the Irpinia earthquake cannot constrain the rheology of the upper mantle but only of the crust; a full search in the viscosity spaces makes it possible to constrain the crustal viscosity to values of the order of 1019 Pa s, in agreement with previous studies carried out in different tectonic environments.
    Description: Published
    Description: 1-16
    Description: partially_open
    Keywords: Lithospheric rheology ; Irpinia earthquake ; 04. Solid Earth::04.01. Earth Interior::04.01.05. Rheology ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 6
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    Connecting seismically active normal faults with Quaternary geological structures in a complex extensional environment: The Colfiorito 1997 case history (northern Apennines, Italy) (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The northern Apennines of Italy are characterized by a complex Tertiary tectonic history, where superposed compressional and extensional deformation occurred. In such regions, characterized by low active extensional strain rate, the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between ‘‘geological’’ faults (i.e., faults which can be mapped at the surface) and ‘‘seismological’’ faults (i.e., faults which actually generate earthquakes). The availability of detailed geological mapping and high-resolution seismological data for the Colfiorito area, struck in 1997 by a sequence of six 5 〈 Mw 6 normal faulting earthquakes, allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological Quaternary faults and the activated structures. In map view, the earthquakes distribution reflects the fault pattern mapped at the surface, the length of activated and mapped faults is quite similar (7–10 km), the coseismic subsided region imaged by interferometric synthetic aperture radar data, is located in the hanging wall of the mapped normal faults that bound the Quaternary basins. In section view, there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth. Comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency. This study points out that the Quaternary tectonosedimentary evolution and the present-day geological and geomorphologic setting of the Colfiorito area can be interpreted as the result of repeated, extensional earthquakes, similar to the 1997 events, occurring on NW-SE trending normal faults. Our data also show that the main shocks of the Colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional/transpressional structures, which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size.
    Description: Published
    Description: TC1002
    Description: reserved
    Keywords: faults ; colfiorito 1997 ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
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  • 7
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    Seismotectonics of the Southern Apennines and Adriatic foreland: insights on active regional E-W shear zones from analogue modeling (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The active tectonics at the front of the Southern Apennines and in the Adriatic foreland is characterized by E-W striking, right-lateral seismogenic faults, interpreted as reactivated inherited discontinuities. The best studied among these is the Molise-Gondola shear zone (MGsz). The interaction of these shear zones with the Apennines chain is not yet clear. To address this open question we developed a set of scaled analogue experiments, aimed at analyzing: 1) how dextral strike-slip motion along a pre-existing zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge; 2) the propagation of deformation as a function of displacement; 3) any insights on the active tectonics of Southern Italy. Our results stress the primary role played by these inherited structures when reactivated, and confirm that regional E-W dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the Southern Apennines.
    Description: INGV, Università degli Studi di Pavia
    Description: Published
    Description: 21
    Description: open
    Keywords: Active strike-slip fault ; sandbox model ; southern Italy ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
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    Great Sumatra Earthquake Registers on Electrostatic Sensor (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Strong electrical signals that correspond to the Mw = 9.3 earthquake of 26 December 2004, which occurred at 0058:50.7 UTC off the west coast of northern Sumatra, Indonesia, were recorded by an electrostatic sensor (a device that detects short-term variations in Earth’s electrostatic fi eld) at a seismic station in Italy, which had been installed to study the infl uence of local earthquakes on a new landslide monitoring system. Electrical signals arrived at the station practically instantaneously and were detected up to several hours before the onset of the Sumatra earthquake (Figure 1) as well as before local quakes. The corresponding seismic signals (p-waves) arrived 740 seconds after the start of the earthquake. Because the electrical signals travel at the speed of light, electrical monitoring for the global detection of very strong earthquakes could be an important tool in signifi cantly increasing the hazard alert window.
    Description: Published
    Description: 445-460
    Description: open
    Keywords: Sumatra earthquake ; electrostatic signals ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    Rock properties of the upper-crust in Central Apennines (Italy) derived from high-resolution 3-D tomography (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: High-resolution 3-D P and S-wave velocity models of a central sector of the Apennines (Central Italy) are computed by inverting first arrival times from an aftershock sequence (September–December, 1997) following the Mw 5.7 and Mw 6.0 Umbria-Marche earthquakes that occurred on September 26, 1997. The high quality of the data set, especially for the S-wave, allows us to compute 3-D variations in Vp, Vp/Vs and Vp · Vs. The anomalies can be interpreted as lateral changes in rock type and fracturing, which control fluid diffusion and variation in pore pressure. This is in agreement with a poro-elastic view that can be inferred from the spatio-temporal evolution of the seismic sequence.
    Description: Published
    Description: 61-4
    Description: open
    Keywords: Physical properties of rocks ; Seismicity and seismotectonics ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 10
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    Teleseismic tomography of the southern Tyrrhenian subduction zone: New results from seafloor and land recordings (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Teleseismic traveltime data, recorded by temporary ocean bottom seismographs deployed in Tyrrhenian Sea around the Aeolian Islands (Tyrrhenian Deep-sea Experiment (TYDE)), have been used for the first time in Italy to refine the 3-D model for the deep P wave velocity structure of the southern Tyrrhenian subduction zone. The arrival times of 35 teleseisms have been combined with those recorded by the Italian National Network. In order to obtain a more complete azimuthal coverage of teleseismic rays, 80 events recorded by land stations from 1990 to 2002 have been included in the data set. In total, 2904 P and 314 PKPdf phases, 1300 recorded by ocean bottom instruments, have been collected. The upper mantle structure is reconstructed down to 500 km by a nonlinear inversion of the relative residuals computed with respect to the reference 1-D velocity model ak135. The obtained tomographic model has a higher resolution than those previously published thanks to the recordings of TYDE seafloor stations. Tomographic results confirm the presence of the Tyrrhenian slab imaged as a high-velocity body extending from the uppermost mantle down to the bottom velocity model with dip 70–75 NW. The model better defines the geometry of the seismogenic part of the slab. Its lateral extension is about 200 km in the depth interval 150–300 km, where most of the deep seismicity is concentrated. At uppermost mantle depths the fast structure has smaller lateral dimensions (about 100 km). The inversion also points out a wide well-resolved low-velocity zone completely surrounding the steeply dipping fast structure from the lower crust down to about 300 km. This feature suggests the presence of a threedimensional circulation of asthenospheric flow around the Ionian slab caused by retreat and roll-back of the slab. Our results are in agreement with recent laboratory experiments, mantle anisotropy studies, geochemical and isotopic analyses, and modeling based on residual topography.
    Description: Published
    Description: B03311
    Description: 3.1. Fisica dei terremoti
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: P-wave teleseismic tomography ; ocean bottom seismometers and hydrophones (OBS/Hs) ; southern Tyrrhenian subduction zone ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 11
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    Simultaneous statospheric aerosol and ozone LIDAR measurements after the Piantubo volcanic eruption (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Preliminary results of simultaneous ozone and aerosol lidar measurements taken in the preriod July-early October 1991 are presented. The main problem for retrieving the ozone profile is the correction of the on and off DIAL signials. The backscattering ratio obtained by the off signal is used for this purpose and ozone profile are validated against ozonesonde data. A number ao cases are oresented including a few occasions of layers with large backscattering ratio.
    Description: ING
    Description: Published
    Description: 393-396
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: JCR Journal
    Description: open
    Keywords: volcanic aerosols ; stratospheric ozone ; 01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous
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  • 12
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    Contemporary total dissolved gas pressure and soil temperature anomalies recorded at Stromboli volcano (Italy) (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Soil temperature and total dissolved gas pressure(TDGP) data were recorded by two continuous monitoring stations on the volcano of Stromboli (Italy) between March and October 2006. During this period several TDGP and soil temperature anomalies, unrelated to external causes and characterized by a similar shape and occurrence time, were recorded. These anomalies were interpreted as transients due to changes in the degassing regime of the volcano,which was in turn related to changes in the partition ratio of the volcanic fluidsbetweenthe conduitandthe soil. In thesame period Stromboli experienced an anomalous phase of volcanic and tectonic activity. The close correlation found between volcano-tectonic activity and variations in anomalousmonitored parameters suggests that their continuous monitoring may be a useful tool for the surveillance of volcanic activity on the island.
    Description: Published
    Description: L08301
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Dissolved gases ; Soil temperature ; Total dissolved gas pressure ; Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 05. General::05.02. Data dissemination::05.02.01. Geochemical data
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  • 13
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    Real-time simultaneous detection of volcanic Hg and SO2 at La Fossa Crater Vulcano (Aeolian Islands, Sicily) (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Measuring Hg/SO2 ratios in volcanic emissions is essential for better apportioning the volcanic contribution to the global Hg atmospheric cycle. Here, we report the first real-time simultaneous measurement Hg and SO2 in a volcanic plume, based on Lumex and MultiGAS techniques, respectively. We demonstrate that the use of these novel techniques allows the measurements of Hg/SO2 ratios with a far better time resolution than possible with more conventional methods. The Hg/SO2 ratios in the plume of F0 fumarole on La Fossa Crater, Vulcano Island spanned an order of magnitude over a 30 minute monitoring period, but was on average in qualitative agreement with the Hg/SO2 ratio directly measured in the fumarole (mean plume and fumarole ratios being 1.09 x 10-6 and 2.9 x 10-6, respectively). The factor 2 difference between plume and fumarole compositions provides evidence for fast Hg chemical processing the plume.
    Description: Published
    Description: L21307
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: JCR Journal
    Description: partially_open
    Keywords: Mercury ; Fumarolic condensates ; Volcanic emissions ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 14
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    Probabilistic eruption forecasting and the call for an evacuation (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One of the most critical practical actions to reduce volcanic risk is the evacuation of people from threatened areas during volcanic unrest. Despite its importance, this decision is usually arrived at subjectively by a few individuals, with little quantitative decision support. Here, we propose a possible strategy to integrate a probabilistic scheme for eruption forecasting and cost-benefit analysis, with an application to the call for an evacuation of one of the highest risk volcanoes: Vesuvius. This approach has the following merits. First, it incorporates a decision-analysis framework, expressed in terms of event probability, accounting for all modes of available hazard knowledge. Secondly, it is a scientific tool, based on quantitative and transparent rules that can be tested. Finally, since the quantitative rules are defined during a period of quiescence, it allows prior scrutiny of any scientific input into the model, so minimizing the external stress on scientists during an actual emergency phase. Whilst we specifically report the case of Vesuvius during the MESIMEX exercise, the approach can be generalized to other types of natural catastrophe.
    Description: Published
    Description: L22310
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: partially_open
    Keywords: evacuation ; probabilistic eruption forecasting ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 15
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    Ground deformations in the Island of Pantelleria (Italy): Insights into the dynamic of the current intereruptive period (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The Island of Pantelleria, located between the coasts of Sicily (Italy) and Tunisia, is deforming due to volcanic and tectonic activity. Here we use electro-optical distance meter, leveling, GPS, and differential interferometry synthetic aperture radar data to constrain the inter-eruptive deformation pattern. We observe subsidence affecting the main caldera of Pantelleria, in the central southern sector of the island. Subsidence is mainly related to hydrothermal cooling and/or fluid withdrawal from a shallow (4 km below sea level) magma chamber located beneath the caldera. The relationships between the caldera area and the remnant part of the island are also investigated through a review of petrographic, geochemical, and structural data.
    Description: INGV-DPC V3-7
    Description: Published
    Description: B11406
    Description: 1.3. TTC - Sorveglianza geodetica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Pantelleria ; Caldera ; SAR ; EDM ; 04. Solid Earth::04.03. Geodesy::04.03.06. Measurements and monitoring
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  • 16
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    Valle del Bove, Eastern Flank of Etna Volcano: a Comprehensive Model for the Opening of the Depression and Implications for Future Hazards (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In this paper we integrate stratigraphic and sedimentological analyses of the volcaniclastic deposits, emplaced during initial opening and later widening of the Valle del Bove depression, with the available stratigraphy of the inner walls, and marine offshore data, structural data, and magnetic surveys to develop a comprehensive model for the opening of the Valle del Bove depression. The resulting model adds new insight into the triggering mechanisms of the flank collapse. Additionally, it suggests a three-stage evolution of the eastern flank of Etna. (1) About 10 Kyr ago, the extinct Ellittico volcano (60 80 (per uniformità anche con Acireale) to 15 Kyr) collapsed, forming the early Valle del Bove. The collapse produced an avalanche deposit that spread ESE and formed the base of the Milo Lahar and the Chiancone deposits. (2) The second stage involved instability-related minor collapses within the valley, causing southward and westward enlargement of the depression and the emplacement of the debris flow sequence that comprises the upper part of the Milo Lahar deposit. (3) Available debris that accumulated within the Valle del Bove from smaller subsequent collapses was deposited at the mouth of the Valle del Bove in the fluvial sequence that forms most of the exposed part of the Chiancone deposit. The emplacement of the whole volcaniclastic sequence occurred between 10 and 2 Kyr ago. Since then, the Valle del Bove has acted as a basin protecting the lower eastern flank of Etna from lava flows or inundations of volcaniclastic debris.
    Description: Published
    Description: 65-75
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: open
    Keywords: Etna ; flank collapse ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 17
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    Fluid flow and seismicity pattern: Evidence from the 1997 Umbria-Marche (central Italy) seismic sequence (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We model the spatial and temporal evolution of seismicity during the 1997 Umbria-Marche seismic sequence in terms of subsequent failures promoted by fluid flow. The diffusion process of pore-pressure relaxation is represented as a pressure perturbation generated by coseismic stress changes and propagating through a fluid saturated medium. The values of isotropic diffusivity range between 22 and 90 m /s. The calculated value of anisotropic diffusivity (Daniso = 250 m /s) is largest along the average strike (N140) direction of activated faults. Our results suggest that the observed spatio-temporal migration of seismicity is consistent with fluid flow.
    Description: Published
    Description: L10311
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Diffusivity ; fluid flow ; Umbria-Marce ; normal fautling ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 18
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    Imaging the complexity of an active normal fault system: The 1997 Colfiorito (central Italy) case study (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Six moderate magnitude earthquakes (5 〈 Mw 〈 6) ruptured normal fault segments of the southern sector of the North Apennine belt (central Italy) in the 1997 Colfiorito earthquake sequence. We study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using1650 earthquake locations obtained by applying a double-difference location method, using travel time picks and waveform cross-correlation measurements. The lateral extent of the fault segments range from 5 to 10 km and make up a broad,45 km long, NW trending fault system. The geometry of each segment is quite simple and consists of planar faults gently dipping toward SW with an average dip of 40–45. The fault planes are not listric but maintain a constant dip through the entire seismogenic volume, down to 8 km depth. We observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure. The observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust: preexisting thrusts inherited from Neogene’s compressional tectonic intersect the active normal faults and control their maximum length. The stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the Apennine, revealing a clear NE trending extension direction. Aftershock focal mechanisms show a consistent extensional kinematics, 70% of which are mechanically consistent with the main shock stress field.
    Description: Published
    Description: 2294,
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Normal faulting ; double-difference ; Umbria-Marche ; corss-correlation ; relative location ; 05. General::05.02. Data dissemination::05.02.02. Seismological data
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  • 19
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    Constraints on mantle circulation around the deforming Calabrian slab (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Combining tectonics, with seismological and geochemical data, we reconstruct the deformation history of the presently narrow Calabrian slab and the path of mantle circulation during the last 10 Ma. We show that during the slab deformation the mantle laterally flowed inside the back arc region permitting its retrograde motion and giving a seismological and volcanological record after 1–2 myr.
    Description: Published
    Description: 1-4
    Description: partially_open
    Keywords: mantle circulation ; Calabrian slab ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.01. Earth Interior::04.01.03. Mantle and Core dynamics ; 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::04.07.06. Subduction related processes
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 20
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    Tectonic evolution of fault-bounded continental blocks: (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We report on new paleomagnetic and anisotropy of magnetic susceptibility (AMS) data from Plio-Pleistocene sedimentary units from Corinth and Megara basins (Peloponnesus, Greece). Paleomagnetic results show that Megara basin has undergone vertical axis CW rotation since the Pliocene, while Corinth has rotated CCW during the same period of time. These results indicate that the overall deformation in central Greece has been achieved by complex interactions of mostly rigid, rotating, fault bounded crustal blocks. The comparison of paleomagnetic results and existing GPS data shows that the boundaries of the rigid blocks in central Greece have changed over time, with faulting migrating into the hanging walls, sometimes changing in orientation. The Megara basin belonged to the Beotia-Locris block in the past but has now been incorporated into the Peloponnesus block, possibly because the faulting in the Gulf of Corinth has propagated both north and east. Paleomagnetic and GPS data from Megara and Corinth basins have significant implications for the deformation style of the continental lithosphere. In areas of distributed deformation the continental lithosphere behaves instantaneously like a small number of rigid blocks with well-defined boundaries. This means that these boundaries could be detected with only few years of observations with GPS. However, on a larger time interval the block boundaries change with time as the active fault moves. Paleomagnetic studies distinguishing differential rotational domains provide a useful tool to map how block boundaries change with time.
    Description: Published
    Description: 1-15
    Description: reserved
    Keywords: Paleomagnetism ; Greece, block rotations ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 21
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    Relationship between tremor and volcanic activity during the Southeast Crater eruption on Mount Etna in early 2000 (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The Southeast Crater of Mount Etna (Italy) was characterized by a violent eruptive activity between 26 January and 24 June 2000. This activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days. We estimated a volume of about 15–20 106 m3 lava and at least 2–3 106 m3 of tephra. We compared the paroxysmal volcanic activity to its associated seismic signature: The high number of events highlighted a strict correlation between tremor and volcanic activity. Seismic and volcanic characteristics, such as the frequency of occurrence, the duration of lava fountains and the associated tremor energy, suggested the subdivision of the studied period into two stages separated by the 20 February event. Combining volcanic with seismic data, we observed some useful relationships among lava fountain height, sustained column height and Reduced Displacement; in addition, we found that the entire episode was well correlated with the duration of the amplitude increase. Computing the tremor energy linked to each event, the total energy associated with lava fountains episodes results in 76% of the energy released during the whole period. Finally, the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode.
    Description: Published
    Description: open
    Keywords: Mount Etna ; lava fountain ; volcanic tremor ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 22
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    Continuos lidar maesurement of stratospheric aerosols and ozone after the Pinatubo eruption. Part II: Time evolution of ozone profiles and of aerosols properties. (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Two lidar systems, an aerosol lidar and an O$_3 DIfferential Absorption Lidar (DIAL), have been routinely operated at the same site (L'Aquila, Italy; 42°N, 13°E) since August 1991. The multiwavelength analysis of the lidar signals allows to retrieve parameters related to equivalent aerosol size distributions and their optical properties. These are needed to correct the ozone DIAL profiles from the disturbance introduced by the stratospheric volcanic aerosols. The method and the confidence of the retrieved ozone profiles are discussed in a companion paper. Here we present the whole measurement series of ozone and backscattering ratio profiles during the period from August 1991 to December 1992. In addition, for some observations, the mode radius and the dispersion of the representative aerosol size distribution are reported. The time evolutions of aerosol surface area density and mass mixing ratio are also discussed within the uncertainties of the retrieval algorithm.
    Description: ING
    Description: Published
    Description: 2869-2872
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: JCR Journal
    Description: open
    Keywords: volcanic aerosols ; stratospheric ozone ; 01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous
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  • 23
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    UARS MLS O3 soundings compared with lidar measurements using the conservative coordinates reconstruction technique (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: A technique based on conservative properties of certain meteorological fields is used to compare ozone measurements from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) with soundings from a lidar system operated at midlatitudes by the University of L'Aquila, Italy. A few typical cases are analyzed in connection with the position of the vortex relative to the observing station, and it is shown that in general lidar observations taken within the vortex compare well with the UARS data,regardless of whether they are coincident with a satellite overpass.It is shown that such analysis may be useful for comparing measurements of the same quantity taken at different sites using different measurement techniques.
    Description: NASA, ING
    Description: Published
    Description: 1535-1538
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: JCR Journal
    Description: open
    Keywords: UARS satellite ; ozone ; 01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous
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  • 24
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    Control of magma flow in dykes on cyclic lava dome extrusion (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time-scales ranging from hours to decades. Examples include Bezymianny volcano (Russia), Merapi (Java), Santiaguito (Guatemala), Mt St Helens (USA), Mt Unzen (Japan), and Soufrie`re Hills volcano (Montserrat). Previous models have assumed simple cylindrical conduits for magma transport, but extrusions are mainly fed by dykes, with cylindrical geometries developing only at shallow levels. The widths of dykes embedded in an elastic medium are influenced by local magma pressure, affecting flow rates and system dynamics strongly. We develop a model for magma flow in dykes, which predicts intense pulsations of magma extrusion for the case of a constant source pressure. The period time scale is determined by the elastic deformation of the dyke walls and the length-to-width ratio of the dyke. The dyke acts like a volumetric capacitor, storing magma as pressure increases and then releasing magma in a pulse of extrusion. For the Soufrie`re Hills volcano, cyclic extrusions with time-scales of a few weeks are predicted for dykes 300–500 m long and 3–6 m wide, matching observations. The model explains the sharp onset of tilt pulsations and seismic swarms.
    Description: Published
    Description: L02303
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Control ; magma flow ; dykes ; cyclic lava ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.04. Thermodynamics
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  • 25
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    Geophysical and hydrogeological experiments from a shallow hydrothermal system at Solfatara Volcano, Campi Flegrei, Italy: Response to caldera unrest (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Integration of high-resolution geophysical and hydrogeological investigations at Solfatara Volcano, Campi Flegrei, Italy, allowed us to (1) image the shallow and intermediate subsurface to the crater, (2) elucidate patterns in the shallow subsurface degassing, and (3) refine and upgrade volcano-monitoring strategies for this dynamic area. Our results show that the subsurface to the crater can be divided roughly into two zones: a dry, outcropping layer overlying a horizon saturated by hydrothermal fluids. Within this saturated zone, intersections of dominant NW- and ENE-striking structural lineaments act as preferential escape conduits for the fluids which generate high microseismic noise amplitudes in the southeastern part of the crater. Hydrogeological data suggest an uprising of the isotherms below Solfatara crater, and a marked increment of fluid degassing, over the last 40 years. Sudden variations of both seismic noise level and noise cycling are positively correlated with early stages of ground inflation during the AD 2000 uplift. We believe therefore that monitoring of seismic noise can be used for upgrading early warning strategies in this sector of the Campi Flegrei volcanic system.
    Description: Published
    Description: B06201
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Geophysical ; hydrogeological ; experiments ; Solfatara ; 03. Hydrosphere::03.02. Hydrology::03.02.02. Hydrological processes: interaction, transport, dynamics ; 03. Hydrosphere::03.04. Chemical and biological::03.04.06. Hydrothermal systems
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  • 26
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    Shallow slab fluid release across and along the Mariana arc-basin system: Insights from geochemistry of serpentinized peridotites from the Mariana fore arc (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Shallow slab devolatilization is not only witnessed through fluid expulsion at accretionary prisms, but is also evidenced by active serpentinite seamounts in the shallow fore-arc region of the Mariana convergent margin. Ocean Drilling Program (ODP) Leg 195 recovered serpentinized peridotites that present a unique opportunity to study the products of shallow level exchanges between the upper mantle and slab-derived fluids. Similar to samples recovered during ODP Leg 125, the protoliths of these fore-arc serpentinized peridotites are mantle harzburgites that have suffered large volume melt extraction (up to 25%) prior to interactions with fluids released from the downgoing Pacific Plate. Samples recovered from both ODP legs 125 and 195 show U-shaped rare earth element (REE) patterns and very low REE abundances (0.001–0.1 chondrites). Relative to global depleted mantle values these rocks typically have 1–2 orders of magnitude lower high field strength elements, REE, Th, and U contents. Interestingly, all fore-arc rocks thus far examined show extreme enrichments of fluid mobile elements (FME: B, As, Cs, Sb, Li). Because the elemental and B, Li, and Sr isotope systematics in these fore-arc serpentinites point to nonseawater-related processes, studies of elemental excesses and anomalous isotopic signatures allow assessment of how much of the subducted inventory is lost during the initial subduction process between 10 and 40 km. On the basis of similar but substantial enrichments of FME in the Mariana fore-arc samples recovered at ODP legs 125 and 195, we report large slab inventory depletions of B ( 75%), Cs ( 25%), As ( 15%), Li ( 15%), and Sb ( 8%); surprisingly low (generally less than 2%) depletions of Rb, Ba, Pb, U, Sr; and no depletions in REE and the high field strength elements (HFSE). Such slab-metasomatized mantle wedge materials may be dragged to depths of arc magma generation, as proposed by Tatsumi (1986) and Straub and Layne (2002) and thus represent an unexplored class of mantle material, different in its origins, physical properties and geochemical fingerprint from mantle rocks traditionally used in modeling a wide range of subduction zone processes.
    Description: Published
    Description: B09205
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: Shallow slab fluid ; Mariana arc-basin ; 04. Solid Earth::04.04. Geology::04.04.05. Mineralogy and petrology ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry
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  • 27
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    Interaction of seismic and airwaves recorded at Stromboli volcano (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Explosion-quake seismograms recorded at Stromboli show that seismic phases with a high-amplitude and high-frequency content propagate with a velocity of approximately 330 m/s - the sound speed. The analysis of seismograms, recorded at a distance of 500 m from one of the three active vents, shows for the first onset a low frequency and particle motion characteristics of a p-wave, which loses its longitudinal polarization with the onset of the air-wave. Recording the explosion-quake simultaneously with a microphonewe would ascertain that the high frequency onset coincides with the air-wave's. In order to better understand the seismic wavefield generated by the atmospheric pressure, we performed a controlled source experiment at Stromboli using a seismic gun. Seismograms with the same two phases and particle motions comparable with the volcanic seismic data were obtained. A second experiment demonstrated, that the air-wave propagates at least in the uppermost 1m of the gound. We suggest that the seismic source of the corresponding seismograms is an explosion at the top of the magma column and conclude that the p- and air-waves are both generated in the same point and at the same time.
    Description: Published
    Description: 65-68
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: volcano seismology ; Stromboli ; air wave ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 28
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    Moment-tensor inversion of LP events recorded on Etna in 2004 using constraints obtained from wave simulation tests (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The persistent occurrence of long period (LP) events at Mt Etna became apparent with the installation of the first fixed broad-band seismic network in late 2003. Repeating similar LP events from Nov. ‘03 to Sept. ‘04 indicate a non-destructive source process. We perform moment tensor (MT) inversions on a stacked high S/N ratio representative LP signal, conducting a grid search for the source geometry and L2-inversion for the source time function. Results indicate a NNW-SSE oriented resonating sub-vertical crack as the most probable source. This result is consistent with deformation and GPS observations. Crucial to this result are constraints imposed by detailed 3D full waveform numerical simulations in a heterogeneous tomographic model with topography, and in particular a detailed assessment of the influence of very near surface velocity structure on LP signals. Pulsating gas injection is hypothesised as the most likely LP trigger.
    Description: Published
    Description: L22316
    Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive
    Description: JCR Journal
    Description: reserved
    Keywords: Etna volcano ; moment tensor inversion ; LP activity ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 29
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    Best-fit results from application of a thermo-rheological model for channelized lava flow to high spatial resolution morphological data (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The FLOWGO thermo-rheological model links heat loss, core cooling, crystallization, rheology and flow dynamics for lava flowing in a channel. We fit this model to laser altimeter (LIDAR) derived channel width data, as well as effusion rate and flow velocity measurements, to produce a best-fit prediction of thermal and rheological conditions for lava flowing in a ~1.6 km long channel active on Mt. Etna (Italy) on 16th September 2004. Using, as a starting condition for the model, the mean channel width over the first 100 m (6 m) and a depth of 1 m we obtain an initial velocity and instantaneous effusion rate of 0.3–0.6 m/s and ~3 m3/s, respectively. This compares with field- and LIDAR-derived values of 0.4 m/s and 1–4 m3/s. The best fit between model-output and LIDAR-measured channel widths comes from a hybrid run in which the proximal section of the channel is characterised by poorly insulated flow and the medial-distal section by well-insulated flow. This best-fit model implies that flow conditions evolve down-channel, where hot crusts on a free flowing channel maximise heat losses across the proximal section, whereas thick, stable, mature crusts of ′a′a clinker reduce heat losses across the medial-distal section. This results in core cooling per unit distance that decreases from ~0.02–0.015°C m−1 across the proximal section, to ~0.005°C m−1 across the medial-distal section. This produces an increase in core viscosity from ~3800 Pa s at the vent to ~8000 Pa s across the distal section.
    Description: Published
    Description: L01301
    Description: 3.6. Fisica del vulcanismo
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: JCR Journal
    Description: reserved
    Keywords: Kava Channel ; LIDAR ; thermal modeling ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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  • 30
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    Advances in the Study of Volcanic Ash (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Every month, small-scale explosive volcanic eruptions inject more than a million cubic meters of ash into Earth’s atmosphere [Simkin and Siebert, 2000]. Of all the troubles caused by this relatively mild volcanic activity, ashfall is by far the longest-reaching one, mantling the volcano slopes and surroundings with a slippery, heavy, unhealthy, and snow-like but Sun-resistant cover. Volcanic ash is composed of pyroclasts (fragments generated and emplaced by explosive eruptions) smaller than 2 millimeters, which are easily transported by wind and have a high surface-to-volume ratio. These same features, however, also allow safe collection of the ash away from the volcano. Such pyroclasts bear the signature of the fragmentation and dispersal processes they have experienced during eruption and transport. Thus, volcanic ash provides sample material well suited for studying quasi time correlated eruption dynamics [Taddeucci et al., 2002]. Here we illustrate how current research projects funded by the Italian Department for Civil Protection combine new sampling, analytical, and experimental techniques to maximize the extraction of useful information from basaltic volcanic ash.
    Description: Published
    Description: 253–260
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: N/A or not JCR
    Description: reserved
    Keywords: Volcanic ; ash ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 31
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    Stress induced elastic anisotropy of the Etnean basalt: Theoretical and laboratory examination (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-03
    Description: A theory, the stress-sensitivity approach, has been developed, which relates the elastic moduli of anisotropic rocks to the stress tensor and pore pressure for an arbitrary symmetry of the applied load. The theory explains the stress-induced changes of seismic velocities in terms of stress-induced changes of the pore space geometry. The stress dependent anisotropy is described in terms of Thomsen’s anisotropy parameters, g and d. To test the theory we analyze the laboratory (high frequency) results of deformation of an isotropically crack damaged dry lava flow basalt from Mt. Etna volcano. The theory states that, under an anisotropic (i.e. axisymmetric triaxial) load and in the case of an initially isotropic rock, (1) the anisotropy parameters are linear functions of the stress exponentials (i. e. exponential functions of principal stress components) and (2) the ratio of these anisotropy parameters as a function of the stress is constant. In order to verify these relationships, the stress exponentials and the anisotropy parameters based on the measured velocities are computed as well as the expected ratio of the Thomsen’s parameters. Our experimental results are in very good agreement with the theoretically predicted relations.
    Description: Published
    Description: L11307
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: rock mechanics applied to volcanoes ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
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  • 32
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    Imaging slow failure in triaxially deformed Etna basalt using 3D acoustic-emission location and X-ray computed tomography (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We have deformed basalt from Mount Etna (Italy) in triaxial compression tests under an effective confining pressure representative of conditions under a volcanic edifice (40 MPa), and at a constant strain rate of 5 10 6 s 1. Despite containing a high level of pre-existing microcrack damage, Etna basalt retains a high strength of 475 MPa. We have monitored the complete deformation cycle through contemporaneous measurements of axial strain, pore volume change, compressional wave velocity change and acoustic emission (AE) output. We have been able to follow the complete evolution of the throughgoing shear fault without recourse to any artificial means of slowing the deformation. Locations of AE events over time yields an estimate of the fault propagation velocity of between 2 and 4 mm/s-1. We also find excellent agreement between AE locations and post-test images from X-ray microtomography scanning that delineates deformation zone architecture. Citation: Benson, P. M., B. D. Thompson, P. G. Meredith, S. Vinciguerra, and R. P. Young (2007), Imaging slow failure in triaxially deformed Etna basalt using 3D acoustic-emission location and X-ray computed tomography
    Description: Published
    Description: L03303
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: JCR Journal
    Description: reserved
    Keywords: fault imaging ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
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  • 33
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    Estimates of slip weakening distance for different dynamic rupture models (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We model the dynamic propagation of a 2-D in-plane crack obeying to either slip weakening (SW) or rate- and state-dependent friction laws (R&S). We compare the value of slip weakening distance (Dc), adopted or estimated from the traction versus slip curves, with the critical slip distance measured as the slip at the time of peak slip velocity (Dc'). The adopted friction law and the constitutive parameters control the slip acceleration as well as the timing and the amplitude of peak slip velocity. Our simulations with R&S show that the direct effect of friction and the friction behavior at high slip rates affect the timing of peak slip velocity and thus control the ratio Dc' /Dc. The difference observed in this study between the Dc values and the inferred Dc' can range between few percent up to 50%.
    Description: Published
    Description: L02611
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Modeling ; Earthquake dynamics and mechanics ; Earthquake parameters ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 34
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    Recent tectonic evolution and present stress in the Northern Apennines (Italy) (2007)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: The present-day stress field and its recent tectonic evolution in the Northern Apennines are reconstructed from borehole breakout analysis and focal mechanisms of crustal earthquakes and through the comparison with paleostress data. We have considered 86 wells for breakout analysis, with depths down to 6–7 km, 125 fault plane solutions of crustal earthquakes with M〈5 that occurred between 1988 and 1995 in the Northern and Central Apennines, and data of stronger earthquakes (M≤6) reported in other studies. The Tyrrhenian coastal region and the Apenninic belt are characterized by Shmin direction mainly trending NE-SW, with predominantly normal fault plane solutions. Along the outer front of the belt and the Adriatic offshore, Shmin is oriented NW-SE, and focal solutions are thrust or strike-slip, with maximum compression around NE-SW. Conversely, south of 43°N, breakouts evidence an orthogonal direction of horizontal compression (NW-SE), following the Southern Apennine trend, where a widespread NE-SW extension was recognized by previous investigations. Comparing these results to the recent tectonic evolution inferred from structural geology, we argue that the extension-compression pair, characteristic of the post-Tortonian evolution of the mountain belt, has been migrating in time from late Miocene to Present only in the northern sector of the arc, whereas the southern sector underwent a generalized extension, at least since middle Pleistocene. The striking correspondence between the active compression front and the region with evidence of a remnant subducted slab suggests that the migrating extension-compression pair has been controlled by progressive retreat of the slab.
    Description: Published
    Description: 108-118
    Description: reserved
    Keywords: stress ; borehole breakout ; tectonics ; Italy ; Apennines ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
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    Along-depth stress rotations and active faults: an example in a 5-km deep well of Southern Italy (2007)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: We have analyzed a 1500 m section at 3.9 to 5.4 km depth in a well of the southern Apennines, in order to better characterize the local active stress field and its correlation with tectonic structures. In this paper we present and discuss the results obtained from the comparison between breakouts and structural analysis from dipmeter data. We have found that the mean breakout direction is in agreement with the regional stress field that in this area is characterized by normal faulting (σ1 = σv) with NE-SW trending extension (horizontal σ3). Since the regional stress field is relatively well known in this region, we could detect and study some anomalous horizontal stress directions along the well, which we interpret as due to faults crosscutting the borehole. A detailed comparison between the breakout-inferred stress variations along depth and the faults identified by the dipmeter analysis reveals that some of these faults are associated with stress rotations, whereas others do not show any variation. The former can be interpreted either as “open” fractures or as faults that slipped recently with a near-complete stress drop, and the latter can be interpreted as “sealed” faults. In particular, we found that the main thrust faults of the area, mainly active in Pliocene times, appear to be sealed, whereas ∼E-W trending high-angle (normal?) faults determine strong stress rotations, suggesting that they are the main active structures of the region. This suggests that the study area is located in a transfer zone between the two main “Apenninic” (NW-SE trending) fault systems which ruptured in the last 150 years. This study has shown that a detailed analysis of the structural and geometrical characteristics of deep wells can be used for the reconnaissance of active structures. This approach can contribute to seismic hazard studies and, if carried out in an oil-bearing section, can help to maximize the hydrocarbon production.
    Description: Published
    Description: reserved
    Keywords: borehole breakout ; structural analysis in deep wells ; active faults ; Southern Apennines ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress
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    The strain path and kinematics of lava domes: An example from Lipari (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: A circular dome from Lipari Island consists of latitic enclaves hosted in a rhyolitic magma. A strain analysis of the enclaves has been carried out and the pure shear (a) and simple shear (g) deformation, the vorticity number Wk and flow kinematics are determined. The axial ratio Rf of the enclaves and the angle f between the long axis of the enclaves and the transport direction are measured in 131 sites concentrated in the axial zone (z1), upper-distal zone (z2) and basal zone (z3) of the flow. The f values depict a pattern suggesting endogenous growth. In z1, a/g 〉 1. In z2, 1 〈 a 〈 1.35 and 1.8 〈 g 〈 0.5. In z3, 1 〈 a 〈 1.5 and 0.3 〈 g 〈 2.8. In z1, Wk 〈 0.5. In z2 and z3, Wk 〉 0.8. Lateral stretching due to the upward motion of magma from the conduit prevails in z1. Here the increase of pure shear strain from the bottom to the top reflects strain accumulation due to endogenous growth. z2 and z3 suffer simple shear deformation. In z3, the sense of shear is consistent with the transport direction. An opposite sense of shear characterizes z2. This is due to velocity gradients located in the lower and upper portions of the flow. The kinematics is viscous spreading in z1 and viscous gliding (hyperbolic flow) in z2â z3.Possible rupturing of the exterior may be important in z1, where lateral stretching occurs, and in z3, where g is at a maximum. The effusion rate is 1.93 m3/s. Strain rates calculated using structural data span a range from 1.9 to 5.8.10 6 s 1.
    Description: Published
    Description: 1-10
    Description: partially_open
    Keywords: lava domes ; kinematics ; emplacement mechanism ; strain analysis ; enclaves ; viscous flows ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
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    Long-duration asynchronous ground motions in the Colfiorito plain, central Italy, observed on a two-dimensional dense array (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In winter 1998 a small-aperture (~200 m), four-station array was operating in the middle of the Colfiorito plain. Waveforms of seven small magnitude (2.1 〈 M 〈 3.7) local earthquakes are analyzed in this study. The peculiarity of the array seismograms is a 2-min long duration of the horizontal ground motion. The predominant frequency in the plain is around 1 Hz. In this frequency band, earthquake-induced ground shaking is synchronous for a few seconds during direct S waves; after this time window, wave trains show an increasingly chaotic behavior within the array. The energy variation of the horizontal ground shaking between the array and a nearby rock outcrop exceeds a factor of 500 at 1 Hz. In order to help understanding of observations and construct models for future numerical simulations, the buried structure of the Colfiorito plain has been investigated through seismic refraction profiles and geoelectric measurements. A three-dimensional reconstruction of the basin structure reveals an extremely complex bedrock topography, which is probably a recurrent feature for intermontane basins in tectonically active regions. Apparent velocities and backazimuths in the frequency band 0.5–1.5 Hz indicate that a 180-m deep depression NW of the array is responsible for the generation of edge-diffracted surface (Love) waves. Their arrival to the array breaks the synchronism of vertically reverberating waves which predominate in the first seconds of the S-wave window
    Description: Published
    Description: reserved
    Keywords: site effects ; 3-D basin resonance ; seismic array ; diffraction ; Colfiorito Basin ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
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    Volcanic spreading of Vesuvius, a new paradigm for interpreting its volcanic activity (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We integrate geologic, structural, leveling and Differential SAR Interferometry data to show that Vesuvius began to spread onto its sedimentary substratum about 3,600 years ago. Moreover, we model the detected deformation with a solution of the lubrication approximation of the Navier-Stokes equations to show that spreading may continue for about 7,200 years more. Correlation of volcanic spreading with phases of the eruptive activity suggests that Plinian eruptions, which are thought to pose the major hazard, are less likely to occur in the near future.
    Description: Published
    Description: 1-4
    Description: partially_open
    Keywords: Vesuvius ; volcanic activity ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.03. Geodesy::04.03.08. Theory and Models
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  • 39
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    Flank instability on Mount Etna: radon, radar interferometry and geodetic data from the south-western boundary of the unstable sector (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Understanding Etnean flank instability is hampered by uncertainties over its western boundary. Accordingly, we combine soil radon emission, InSAR and EDM data to study the Ragalna fault system (RFS) on the SW flank of the volcano. Valuable synergy developed between our differing techniques, producing consistent results and serving as a model for other studies of partly obscured active faults. The RFS, limited in its surface expression, is revealed as a complex interlinked structure ~14 km long that extends from the edifice base towards the area of summit rifting, possibly linking north-eastwards to the Pernicana fault system (PFS) to define the unstable sector. Short-term deformation rates on the RFS from InSAR data reach ~7 mm a-1 in the satellite line of sight on the upslope segment and ~5 mm a-1 on the prominent central segment. While combining this with EDM data confirms the central segment of the RFS as a dextral transtensive structure, with strike-slip and dip-slip components of ~3.4 and ~3.7 mm a-1 respectively. We measured thoron (220Rn, half-life 56 secs) as well as radon and, probably because of its limited diffusion range, this appears a more sensitive but previously unexploited isotope for pinpointing active near-surface faults. Contrasting activity of the PFS and RFS reinforces proposals that the instability they bound is divided into at least three sub-sectors by intervening faults, while, in section, fault-associated basal detachments also form a nested pattern. Complex temporal and spatial movement interactions are expected between these structural components of the unstable sector.
    Description: Published
    Description: B04410
    Description: JCR Journal
    Description: partially_open
    Keywords: Multidisciplinary study; Ragalna fault system; radon and thoron; InSAR; EDM; volcano collapse models ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology
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    Continuos lidar maesurement of stratospheric aerosols and ozone after the Pinatubo eruption. Part I: Dial ozone retrieval in presence of stratospherical aerosol layers (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We report stratospheric DIAL (DIfferential Absorption Lidar) ozone observations in presence of large amount of volcanic aerosols, which strongly affect the inversion of the backscattering signals. The retrieval method is based on the use of three wavelengths, two from the O3 DIAL (308 and 351nm) and a third one from an aerosol lidar (589nm) operated at the same site (L'Aquila, Italy; 42°N,13°E). For each measurement session the relationships between the backscattering ratios at different wavelengths are fitted with an appropriate size distribution of the aerosols. The aerosol optical properties determined with this procedure allow to correct the ozone profiles. The ozone data are compared whenever possible with balloon ozonesonde measurements taken at S.Pietro Capofiume (Italy, 45°N, 11°E) or Hohenpeissenberg (Germany, 48°N, 11°E) and they generally show a good agreement. The ozone profiles can be retrieved with an indetermination that, within the aerosol layer, ranges between +-15 to +-35%. A systematic intercomparison is reported with data of other stations to assess the reliability of the method.
    Description: ING
    Description: Published
    Description: 2865-2568
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: JCR Journal
    Description: open
    Keywords: volcanic aerosol ; stratospheric ozone ; 01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous
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    Comparing simoultaneous stratospheric aerosol and ozone lidar measurements with SAGE II data after the Mount Pinatubo eruption (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Stratospheric aerosol and ozone profiles obtained simoultaneosly from the lidar station at the university of L'Aquila during the first 6 months following the eruption of Mount Pinatubo are compared with corresponding nearby Stratosperic Aerosol and Gas Experiment (SAGE) II profiles. The agreement between the two data stes is found to be reasonably good. The temporal change of aerosol profiles obtained by both technique showed the intrusion and growth of Pinatubo aerosols. In addition, ozone concntration profiles derivide from an empirical time-series model based on SAGE II ozone data obtained bifore the Pinatubo eruption are compared with measured profiles. Good agreement is shown in the 1991 profiles, but ozone concentration measured in January 1992 were reduced relative ti time-series model estimates. Possible reasons for the diffrences between measured and model-based ozone profiles are discussed.
    Description: NASA ING
    Description: Published
    Description: 1881-1884
    Description: 1.8. Osservazioni di geofisica ambientale
    Description: JCR Journal
    Description: open
    Keywords: volcanic aerosols ; ozone ; 01. Atmosphere::01.01. Atmosphere::01.01.99. General or miscellaneous
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    Micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are lognormal shaped, with Bjurbole distributions being bimodal or trimodal. The highest-coercivity mode in the Bjurbole chondrules is derived from tetrataenite, which interacts strongly with the lower-coercivity grains in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is 〈10 mT, low-coercivity magnetic overprints are common. Therefore paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early solar system, have a mean REMc paleointensity of 10.4 μT. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 μT, respectively.
    Description: NSF and INGV
    Description: Published
    Description: B03S90
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: reserved
    Keywords: paleomagnetism coercivity ; paleointensity ; magnetic interactions ; meteorite ; Chondrules ; FORC diagrams ; 01. Atmosphere::01.03. Magnetosphere::01.03.01. Interplanetary physics
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    4D simulation of explosive eruption dynamics at Vesuvius (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We applied a new simulation model, based on multiphase transport laws, to describe the 4D (3D spatial coordinates plus time) dynamics of explosive eruptions. Numerical experiments, carried out on a parallel supercomputer, describe the collapse of the volcanic eruption column and the propagation of pyroclastic density currents (PDCs), for selected medium scale (sub-Plinian) eruptive scenarios at Vesuvius, Italy. Simulations provide crucial insights into the effects of the generation mechanism of the flows - partial collapse vs boiling-over - on their evolution and hazard potential, the unstable dynamics of the fountain, and the influence of Mount Somma on the propagation of PDCs into the circum-Vesuvian area, one of the world's most hazardous volcanic settings. Results also show that it is possible to characterize the volcanic column behavior in terms of percentage of the mass of pyroclasts collapsed to the ground and how this parameter strongly influences the dynamics and hazard of the associated PDCs.
    Description: Published
    Description: L04309
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: explosive eruption ; numerical modeling ; Vesuvius ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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    Holocene tsunamis from Mount Etna and the fate of Israeli Neolithic communities (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Field evidence reveals that the Neolithic village of Atlit-Yam (Israeli coast) was destroyed in an event which also caused the sudden death of tens of inhabitants. Archaeological evidence and numerical simulations support the notion that the village was destroyed, ~8.3 ka B.P., by a tsunami triggered by a known Holocene flank collapse of Mt. Etna volcano (Italy). The filling of a water well within the village confirms inundation by a tsunami wave train and a sediment layer, composed of a clayed-sandy matrix and other detritus including reworked marine sediment, indicates tsunami inundation. This scenario shows that tsunamis generated by sector collapses from coastal volcanoes can seriously threaten near-shore settlements thousands of kilometres distant from the tsunami source.
    Description: Published
    Description: L16317
    Description: 4.3. TTC - Scenari di pericolosità vulcanica
    Description: JCR Journal
    Description: reserved
    Keywords: tsunami ; Mt. Etna ; Atlit-Yam ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
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  • 45
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    The dependence of traction evolution on the earthquake source time function adopted in kinematic rupture models (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We compute the temporal evolution of traction by solving the elasto-dynamic equation and by using the slip velocity history as a boundary condition on the fault plane. We use different source time functions to derive a suite of kinematic source models to image the spatial distribution of dynamic and breakdown stress drop, strength excess and critical slip weakening distance (Dc). Our results show that the source time functions, adopted in kinematic source models, affect the inferred dynamic parameters. The critical slip weakening distance, characterizing the constitutive relation, ranges between 30% and 80% of the total slip. The ratio between Dc and total slip depends on the adopted source time functions and, in these applications, is nearly constant over the fault. We propose that source time functions compatible with earthquake dynamics should be used to infer the traction time history.
    Description: Published
    Description: L04609
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: partially_open
    Keywords: Earthquake dynamics and mechanics ; Earthquake parameters ; Theory and modeling ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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  • 46
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    Earthquake fracture energy inferred from kinematic rupture models on extended faults (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms. We define the breakdown work (Wb) as the excess of work over some minimum traction level achieved during slip. Wb is equivalent to "seismological" fracture energy (G) in previous investigations. Our numerical approach uses slip velocity as a boundary condition on the fault. We employ a three-dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture. We estimate Wb by calculating the scalar product between dynamic traction and slip velocity vectors. This approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity. If these vectors are not collinear, the inferred breakdown work depends on the initial traction level. We show that breakdown work depends on the square of slip. The spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution. Breakdown work density and its integral over the fault, breakdown energy, scale with seismic moment according to a power law (with exponent 0.59 and 1.18, respectively). Our estimates of breakdown work range between 4e+5 and 2e+7 J/m2 for earthquakes having moment magnitudes between 5.6 and 7.2. We also compare our inferred values with geologic surface energies. This comparison might suggest that breakdown work for large earthquakes goes primarily into heat production.
    Description: Published
    Description: B12303
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Earthquake dynamics and mechanics ; Earthquake modeling ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
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    High quality seismological recordings from the SN-1 deep seafloor observatory in the Mt. Etna region (2006)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We show over 4 months of 3-component broadband seismometer data from the SN-1 seafloor multidisciplinary observatory, deployed offshore of Eastern Sicily (Italy) at 2105 m b.s.l. The SN-1 spectra show background noise levels above 0.1 Hz similar to levels at a nearby ground station. An important noise source below 0.1 Hz is caused by tilt of the sensor induced by sea currents. Seismic noise levels above 0.01 Hz are strongly dependent on Etna volcanic activity. In spite of these intense noise sources, SN-1 recorded many local, regional and global events. The quality of seismic recordings confirms the validity of the installation procedure and good ground coupling of the 3-component broadband sensor, suggesting that SN-1 can be proposed as permanent observatory in this high seismic and volcanic hazard area.
    Description: 2002-2003 Framework Program of the Italian National Group for the Defense against Earthquakes (GNDT)
    Description: Published
    Description: L07303
    Description: reserved
    Keywords: 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
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  • 48
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    Crustal motion along the Eurasia-Nubia plate boundary (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-03
    Description: We investigate crustal deformation along the Eurasia-Nubia plate boundary in Calabria and Sicily revealed by the GPS velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns. We recognize two distinct crustal domains characterized by different motions and styles of deformation. Convergence in Sicily is taken up by crustal shortening along the former Tyrrhenian back arc passive margin, in agreement with seismological data and geological evidence of recent cessation of deformation along the Plio-Pleistocene subduction front. The analysis of the GPS data and the consistency between earthquake slip vectors and convergence direction suggest that Eu-Nu convergence in Sicily does not require intermediate crustal blocks. Significant Eurasia ( 3 mm/yr to NNE) and Nubia-fixed ( 5 mm/yr to ESE) residual velocities in Calabria suggest instead the presence of an intermediate crustal block which can be interpreted as a forearc sliver or as an independent Ionian block. According to the first hypothesis, subduction is still active in the Ionian wedge, although we find no evidence for active back arc spreading in the Tyrrhenian Sea. The N115 E oriented Sicily-Calabria GPS relative motion is consistent with the extension observed during the 1908 Mw 7.1 Messina earthquake. We suggest that up to 3 mm/yr ( 80%) of this estimated relative motion between Sicily and the Calabrian Arc may be taken up in the Messina Straits.
    Description: Published
    Description: 1-16
    Description: reserved
    Keywords: GPS ; Calabria, Sicily, Active tectonics ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 49
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    Active crustal extension in the central Apennines (Italy) (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present the first GPS estimate of crustal extension in the central Apennines (Italy) through the analysis of the deformation of a sub-network of the National GPS Geodetic network IGM95 in the interval 1994–1999. The selected sub-network spans the entire active deformation belt perpendicularly to its axis and allows the evaluation of (1) the total extension rate absorbed in this sector of the Apennines and (2) the seismogenic potential of the normal faults active in the Late Pleistocene-Holocene interval within the network. Results of this reoccupation are consistent with an extensional strain rate of 0.18×10−6 yr−1 concentrated in an area of about 35 km width, giving an average extension rate of 6±2 mm/yr across the central Apennines. The pattern of active deformation suggests active elastic strain accumulation on the westernmost of the two fault systems active in the Late Pleistocene-Holocene interval and may also suggest the presence of another active fault system not recognized so far.
    Description: Published
    Description: 2121-2124
    Description: reserved
    Keywords: GPS ; Apennines, Active extension ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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    Pyroclastic flow dynamics and hazard in a caldera setting: application to Phlegrean Fields (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Numerical simulation of pyroclastic density currents has developed significantly in recent years and is increasingly applied to volcanological research. Results from physical modeling are commonly taken into account in volcanic hazard assessment and in the definition of hazard mitigation strategies. In this work, we modeled pyroclastic density currents in the Phlegrean Fields caldera, where flows propagating along the flat ground could be confined by the old crater rims that separate downtown Naples from the caldera. The different eruptive scenarios (mass eruption rates, magma compositions, and water contents) were based on available knowledge of this volcanic system, and appropriate vent conditions were calculated for each scenario. Simulations were performed along different topographic profiles to evaluate the effects of topographic barriers on flow propagation. Simulations highlighted interesting features associated with the presence of obstacles such as the development of backflows. Complex interaction between outward moving fronts and backflows can affect flow propagation; if backflows reach the vent, they can even interfere with fountain dynamics and induce a more collapsing behavior. Results show that in the case of large events ( 108 kg/s), obstacles affect flow propagation by reducing flow velocity and hence dynamic pressure in distal regions, but they cannot stop the advancement of flows. Deadly conditions (in terms of temperature and ash concentration) characterize the entire region invaded by pyroclastic flows. In the case of small events (2.5 107 kg/s), flows are confined by distal topographic barriers which provide valuable protection to the region beyond.
    Description: Published
    Description: Q11003
    Description: open
    Keywords: Phlegrean Fields ; multiphase flow ; pyroclastic flows ; dynamic pressure ; volcanic hazard ; caldera ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Evidence for departure in self-similarity: a new spectral ratio method using narrowband coda envelopes (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: The use of local and regional S-wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs. We first compared amplitude ratio performance between local and near regional S and coda waves in the San Francisco Bay region for moderate-sized events, then applied the coda spectral ratio method to the 1999 Hector Mine mainshock and its larger aftershocks. We find (1) average amplitude ratio standard deviations using coda are ~0.05 to 0.12, roughly a factor of 3 smaller than direct S-waves for 0.2 〈 f 〈 15.0 Hz; (2) coda spectral ratios for the Mw 7.0 Hector Mine earthquake and its aftershocks show a clear departure from self-similarity, consistent with other studies using the same datasets; and (3) event-pairs (Green’s function and target events) can be separated by ~25 km for coda amplitudes without any appreciable degradation, in sharp contrast to direct waves.
    Description: Published
    Description: L11303
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: non-self-similarity ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
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    Lava flow identification and aging by means of lidar intensity: Mount Etna case (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: An application of light detection and ranging (lidar) intensity for the identification and mapping of different lava flows from the Mount Etna (Italy) active volcano is described. In September 2004 an airborne lidar survey was flown over summit sectors of Mount Etna. The information derived from lidar intensity values was used to compare the lava flows with respect to their age of emplacement. Analyzed lava flows vary in age between those dating prior to A.D. 1610 and those active during the survey (2004–2005 eruptions). The target-emitter distance, as well as surface roughness and texture at the lidar footprint scale, is the main parameter controlling the intensity response of lava flows. Variations in the roughness and texture of surfaces at a meter scale result from two main processes, initial lava cooling and subsequent surface weathering; both lead to variations in the original surface roughness of the flow. In summary: (1) initially, from the time of emplacement, the lidar intensity of lava flow surfaces decreases and (2) about 6 years after emplacement the lidar intensity of lava surfaces starts to increase with the age of flows. Lidar capability in terms of geometric (accuracy of ∼1 m in plan position and less than 1 m in elevation) and spectral (lidar intensity depends on surface reflection at λ = 1.064 μm) information can thus be effectively used to map lava flows and to define a relative chronology of lava emplacement.
    Description: Published
    Description: B02201
    Description: 3.6. Fisica del vulcanismo
    Description: 3.5. Geologia e storia dei sistemi vulcanici
    Description: JCR Journal
    Description: reserved
    Keywords: lava flows ; mapping ; lidar ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
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    Empirical ground-motion prediction equations for Northwestern Turkey using the aftershocks of the 1999 Kocaeli earthquake (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We present ground motion models for northwestern Turkey using the aftershocks of the Mw 7.4, 1999 Kocaeli earthquake. We consider 4047 velocity and acceleration records for each component of motion, from 528 earthquakes recorded by stations belonging to regional networks. The ground motion models obtained provide peak ground velocity, peak ground acceleration, and spectral accelerations for 8 different frequencies between 1 and 10 Hz. The analysis of the error distribution shows that the record-to-record component of variance is the largest contribution to the standard deviation of the calibrated ground- motion models. Furthermore, a clear dependence of inter-event error on stress drop is observed. The empirical ground-motion prediction equations, derived for both the larger horizontal and vertical components, are valid in the local magnitude range from 0.5 to 5.9, and for hypocentral distances up to 190 km. Citation: Bindi, D., S. Parolai, H. Grosser, C. Milkereit, and E. Durukal (2007), Empirical ground-motion prediction equations for northwestern Turkey using the aftershocks of the 1999 Kocaeli earthquake,
    Description: Published
    Description: L08305
    Description: 4.1. Metodologie sismologiche per l'ingegneria sismica
    Description: JCR Journal
    Description: partially_open
    Keywords: Attenuation relationship ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
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    Coseismic and postseismic displacements related with the 1997 earthquake sequence in Umbria-Marche (central Italy) (2007)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We study the coseismic and postseismic displacements related with the 1997 Umbria-Marche earthquake sequence by means of leveling lines along a deformed aqueduct located in the epicentral area. Comparing the 1960 and 10/1997 measurements we obtain 0.49 0.10 m of coseismic displacement distributed along 3 km across the normal fault zone. Modeling of the coseismic surface dislocation is obtained from a combination of low angle (38°) faults at depth and high angle (80°) upper fault branches. The best fit model indicates that the upper branches stop at 0.4 km below the ground surface and have 60% of slip with respect to the lower faults. The postseismic displacement measured during 1998 is 0.18 m and represents 36% of the apparent coseismic deformation. Moderate earthquakes in the Apennines and related surface deformation may thus result from curved faults that reflect the brittle-elastic properties of the uppermost crustal structures.
    Description: Data collection was made while both authors were at Istituto di Ricerca per la Tettonica Recente – CNR (GNDT Project), Roma, Italy. M. Copparoni (ASM, Foligno) and M. Raponi and S. Pacico (Studio Topografico s.n.c., Foligno) provided data about aqueduct and leveling lines. Analysis of data and modeling were done while RB was visiting EOST-IPG, Strasbourg, France. Preparation of the paper benefited from discussion with R. Armijo, S. Barba, P. Gomez and G. Valensise. A. Amato and an anonymous reviewer are thanked for their constructive remarks.
    Description: Published
    Description: 2695–2698
    Description: JCR Journal
    Description: open
    Keywords: Coseismic displacement ; postseismic displacement ; earthquake fault ; Colfiorito, Italy ; 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::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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    Thermo-rheological magma control on the impact of highly fluid lava flows at Mt. Nyiragongo (2007)
    American Geophysical Union
    Details
    Publication Date: 2020-05-29
    Description: In January 2002 Mount Nyiragongo erupted foiditic lavas that covered the Southern volcano flank devastating vast urban areas. Lava flows originated from vents at different heights on the eruptive fissure displayed different velocities, from tens of km/h at the highest vents to slow-advance (0.1–1 km/h) in Goma town several km away from the volcano. To understand the different behavior of lava flows and their threat to the local population, we undertook a multidisciplinary study involving textural and rheological measurements and numerical simulations of heat transfer during magma ascent. We demonstrate that pre-eruptive cooling and syn-eruptive undercooling of magma determined the different rheological behavior of lava flows erupted from vents at diverse heights. Venting at lower altitudes is expected to produce viscous, slowly advancing lavas, although development of fluid, faster flows should be included among possible future eruptive scenarios.
    Description: Published
    Description: L06301
    Description: 3.6. Fisica del vulcanismo
    Description: JCR Journal
    Description: reserved
    Keywords: Nyiragongo volcano ; textural and rheological measurements ; numerical simulations ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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    Spatial and temporal variability of oceanic heat flux to the Arctic ice pack (2006)
    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 Journal of Geophysical Research 110 (2005): C07021, doi:10.1029/2004JC002293.
    Description: In order to simulate the large-scale structure and temporal variability of oceanic heat flux (F w) to the Arctic perennial ice pack, observations of heat in the mixed layer and ice dynamics are compared with parameterizations and climatologies. Long-term drifting platform observations of seawater temperature and salinity (primarily from automated buoys) are used to describe the annual cycle of temperature above freezing (ΔT f) in the mixed layer beneath the ice pack, which are modulated by ice-ocean friction velocities (u*) determined from the platform drifts to produce estimates of F w between 1975 and 1998. On average, ΔT f is not negligible in winter, especially in the Transpolar Drift, which implies a positive F w to the ice pack by means other than solar heating. A parameterization based solely on the solar zenith angle (with a 1 month lag) is found to largely describe the observed ΔT f (with root mean square error of 0.03°C), despite the lack of an albedo or open water term. A reconstruction of F w from 1979 to 2002 is produced by modulating parameterized ΔT f with u* on the basis of daily ice drift estimates from a composite satellite and in situ data set. The reconstructed estimates are corrected for regional variations and are compared to independent estimates of F w from ice mass balance measurements, indicating annual F w averages between 3 and 4 W m−2 depending on the selection of under-ice roughness length in the ice-ocean stress calculations. Although the interannual variations in ΔT f are fixed by the parameterization in the derived reconstruction, the dynamics indicate an overall positive trend (0.2 W m−2 decade−1) in Arctic F w, with the largest variations found in the southern Beaufort Gyre.
    Description: Portions of this work were prepared with funding provided by the International Arctic Research Center and National Science Foundation ARCSS program (grant OPP-0230184). Analysis of the IOEB data was accomplished as part of the IOEB program, which was supported by the Office of Naval Research, High Latitude Program, and Japan Marine Science and Technology Center.
    Keywords: Oceanic heat flux ; Arctic ice pack ; Ice-ocean interactions
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    Growth and composition of high-Mg calcite in the skeleton of a Bermudian gorgonian (Plexaurella dichotoma) : potential for paleothermometry (2006)
    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 Geochemistry Geophysics Geosystems 6 (2005): Q08010, doi:10.1029/2005GC000911.
    Description: We used Secondary Ion Mass Spectrometry (SIMS) ion microprobe to analyze magnesium-to-calcium (Mg/Ca) and strontium-to-calcium (Sr/Ca) ratios of high-Mg calcite loculi within the skeleton of a shallow water gorgonian, Plexaurella dichotoma, from Bermuda. A cross-section of the gorgonian skeleton reveals loculi embedded within proteinaceous gorgonin arranged in concentric rings about the axial core. Viewed in cross-section, the loculi are fan-shaped, 10-140 μm in diameter, and composed of bundles of needle-shaped crystals that appear to radiate out from a calcification center. Discrete sample spots, each 20 μm diameter, were sputtered from successive loculi along a sample track 3 mm long. Over this distance, twenty-five bands of high-low density gorgonin couplets were encountered, estimated to represent the period 1963 to 1988. Mg/Ca ratios show an overall, positive correlation with annual sea surface temperatures (SSTs) that is strongest in the autumn months (October- December). High-resolution analyses along the growth axes of individual loculi reveal low variability and no trend, consistent with our interpretation of seasonal growth of these calcite inclusions. The sensitivity of Mg/Ca to interannual changes in average autumn temperatures is 0.47 mmol/mol per ºC. Conversely, interannual variability in calcite Sr/Ca does not follow the interannual variability in SST and may be influenced primarily by growth rate.
    Description: This study was supported by an Independent Study Award from the Woods Hole Oceanographic Institution No. 270051.81; NERC grant GR3/12800; a WHOI Ocean Life Institute grant to ALC; Bermuda Government, in support of the Benthic Ecology Research Programme at BBSR to SRS. Support for the WHOI Northeast National Ion Microprobe Facility was provided by NSF EAR-9628749.
    Keywords: Gorgonian ; Octocoral ; Mg/Ca ; Sr/Ca ; Sea surface temperature ; Biomineralization ; Growth bands ; SIMS ion microprobe ; Bermuda
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    Emission of dimethylsulfide from Weddell Sea leads (2006)
    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): L23610, doi:10.1029/2005GL024242.
    Description: The distribution of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) was examined in lead water in pack ice of the Weddell Sea. Samples were taken by pulling water into a syringe from a series of depths from 0.002 m to 4 m and deeper. Concentrations of DMS, DMSP and DMSO remained low throughout the water column relative to surface water, which was highly enriched. Concentrations of the major sulfur compounds increased by over an order of magnitude during periods with smooth surface water conditions. This increase coincided with a profound stratification of the water column, caused by a decrease in salinity of near surface water. We estimate that the DMS emission from leads and open water in Antarctic sea ice could contribute significantly to the yearly DMS flux from the Southern Ocean.
    Description: This work was financially supported by the Marie Currie Training Site Fellowship (contract number HPMF-CT-2002-01865) and by Natural Environment Research Council, UK (award ref number NER/B/S/2003/00844).
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    Channelized lava flows at the East Pacific Rise crest 9°–10°N : the importance of off-axis lava transport in developing the architecture of young oceanic crust (2006)
    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 Geochemistry Geophysics Geosystems 6 (2005): Q08005, doi:10.1029/2005GC000912.
    Description: Submarine lava flows are the building blocks of young oceanic crust. Lava erupted at the ridge axis is transported across the ridge crest in a manner dictated by the rheology of the lava, the characteristics of the eruption, and the topography it encounters. The resulting lava flows can vary dramatically in form and consequently in their impact on the physical characteristics of the seafloor and the architecture of the upper 50–500 m of the oceanic crust. We have mapped and measured numerous submarine channelized lava flows at the East Pacific Rise (EPR) crest 9°–10°N that reflect the high-effusion-rate and high-flow-velocity end-member of lava eruption and transport at mid-ocean ridges. Channel systems composed of identifiable segments 50–1000 m in length extend up to 3 km from the axial summit trough (AST) and have widths of 10–50 m and depths of 2–3 m. Samples collected within the channels are N-MORB with Mg# indicating eruption from the AST. We produce detailed maps of lava surface morphology across the channel surface from mosaics of digital images that show lineated or flat sheets at the channel center bounded by brecciated lava at the channel margins. Modeled velocity profiles across the channel surface allow us to determine flux through the channels from 0.4 to 4.7 × 103 m3/s, and modeled shear rates help explain the surface morphology variation. We suggest that channelized lava flows are a primary mechanism by which lava accumulates in the off-axis region (1–3 km) and produces the layer 2A thickening that is observed at fast and superfast spreading ridges. In addition, the rapid, high-volume-flux eruptions necessary to produce channelized flows may act as an indicator of the local magma budget along the EPR. We find that high concentrations of channelized lava flows correlate with local, across-axis ridge morphology indicative of an elevated magma budget. Additionally, in locations where channelized flows are located dominantly to the east or west of the AST, the ridge crest is asymmetric, and layer 2A appears to thicken over a greater distance from the AST toward the side of the ridge crest where the channels are located.
    Description: This work was supported by NSF grant OCE-9819261 (to H.S., M.A.T., and D.J.F.) as well as the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Penzance Endowed Discretionary Fund.
    Keywords: Channels ; Lava ; Lava morphology ; Ridge-crest ; Submarine
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    FOZO, HIMU, and the rest of the mantle zoo (2006)
    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 Geochemistry Geophysics Geosystems 6 (2005): Q05007, doi:10.1029/2004GC000824.
    Description: The parameter μ describes the 238U/204Pb ratio of an Earth reservoir. Mantle domains labeled HIMU (high μ) originally defined reservoirs with highly radiogenic Pb isotope ratios observed in basalts from a select number of ocean islands, St. Helena in the Atlantic Ocean and the Cook-Austral islands in the South Pacific Ocean. While some authors use the term HIMU in this original sense, others refer to HIMU as a widespread component in many mid-ocean ridge and ocean island basalt (MORB and OIB) sources. Here we show that highly radiogenic Pb isotope signatures in MORB and OIB originate from two different sources. In addition to the classical HIMU component observed at St. Helena and the South Pacific (named HIMU in the following), we define a component with slightly less radiogenic Pb but significantly more radiogenic Sr isotope signatures. This component lies at the extension of the (Atlantic and Pacific) MORB array in a Sr-Pb isotope ratio diagram and is argued to be a ubiquitous component in MORB and many OIB sources. The inferred role of this component in the mantle and its inferred genetic origin closely resemble those originally suggested for a mantle component termed FOZO by Hart and coworkers. By redefining the composition, the origin, and the role of FOZO in the mantle, we establish a simple conceptual framework that explains the isotopic variability in both MORB and OIB with the lowest number of components. OIB are grouped into HIMU-type OIB and basalts from islands that diverge from the MORB-FOZO array toward various isotopically “enriched” compositions (EM). The apparent ubiquity of FOZO in the mantle and the calculated isotopic evolution of compositionally diverse MORB suggest that normal mantle melting and continuous subduction and aging of that crust during recycling through the mantle are the dominant causes of the MORB-FOZO array. In contrast to FOZO, HIMU-type OIB are quite rare, and if an origin by recycling of oceanic crust is also postulated, the production of HIMU sources has to be a special and rare combination of age and composition of subduction-modified recycled oceanic crust.
    Description: This work is partially supported by the Deutsche Forschungsgmeinschaft (DFG grant STR853/1 to A.S).
    Keywords: FOZO ; HIMU ; MORB ; Oceanic basalts ; OIB
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    Evidence for an extensive hydrothermal plume in the Tonga-Fiji region of the South Pacific (2006)
    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 Geochemistry Geophysics Geosystems 5 (2004): Q01003, doi:10.1029/2003GC000607.
    Description: Several hydrographic stations in the vicinity of the Samoa Islands have 3He/4He above the regional background in the depth range of 1500–1800 m, indicating injection of mantle helium from a local hydrothermal source. The highest δ(3He) = 43.4% was detected at 1726-m depth at 15.0°S, 173.1°W in the bathymetric gap between the Samoa Islands and the northern end of the Tonga-Kermadec Arc. The δ(3He) profile at this station decreases to δ(3He) = 26% at 2500-m depth. The relatively shallow depth of the maximum hydrothermal signal suggests a source different from the conventional Pacific basin helium plume centered at 2500 m that is carried westward from the East Pacific Rise. Stations to the west of this locality show a progressive decrease in the maximum δ(3He) values in the depth range of 1480–1790 m out to 169°E. Stations east of the Tonga-Fiji region show lower 3He values (〈26%) at 1700 m and the profiles are dominated by a deeper maximum at 2500 m, presumably the distal traces of hydrothermal input from East Pacific Rise. This pattern in the 3He distribution suggests that the 1700-m deep helium plume is carried in a northwesterly direction some 2000 km from its source near the northern end of the Tonga-Kermadec Arc. At this time very little is known about the source of this hydrothermal plume or the details of its areal extent. Numerous seamounts and rift zones in the region are possible hydrothermal sources for the plume. The summit crater of Vailulu'u, a young seamount at the eastern end of the Samoa chain, was recently discovered to be hydrothermally active at ∼600 m depth [Hart et al., 2000]. However this shallow hydrothermal field on Vailulu'u is an unlikely source for the deeper 1700-m signal. The most likely source would appear to be the extensional zones of the northern Lau Basin system, such as the Mangatolo Triple Junction. Just as the helium plume emanating from Lo'ihi has helped our understanding of the circulation near the Hawaiian Islands [Lupton, 1996], this helium plume in the Tonga-Fiji region has great potential for delineating circulation in this area of the south Pacific.
    Description: This work was supported by the NOAA Vents Program and by Grants OCE91-05884, OCE92-96237, OCE92-96169, and OCE98-20132 of the Ocean Sciences Division of the National Science Foundation.
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    Quantitative bedrock geology of east and Southeast Asia (Brunei, Cambodia, eastern and southeastern China, East Timor, Indonesia, Japan, Laos, Malaysia, Myanmar, North Korea, Papua New Guinea, Philippines, far-eastern Russia, Singapore, South Korea, Taiwan, Thailand, Vietnam) (2006)
    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 Geochemistry Geophysics Geosystems 5 (2004): Q01B06, doi:10.1029/2003GC000619.
    Description: We quantitatively analyze the area-age distribution of sedimentary, igneous and metamorphic bedrock based on data from the most recent digital geologic maps of East and Southeast Asia (Coordinating Committee for Coastal and Offshore Geosciences Programmes in East and Southeast Asia (CCOP) and the Geologic Survey of Japan, 1997; 1:2,000,000), published as Digital Geoscience Map G-2 by the Geological Survey of Japan. Sedimentary rocks, volcanic rocks, plutonic rocks, ultramafic rocks and metamorphic rocks cover 73.3%, 8.5%, 8.8%, 0.9%, and 8.6% of the surface area, respectively. The average ages of major lithologic units, weighted according to bedrock area, are as follows: sedimentary rocks (average stratigraphic age of 123 Myr/median age of 26 Myr), volcanic rocks (84 Myr/20 Myr), intrusive rocks (278 Myr/195 Myr), ultramafic rocks (unknown) and metamorphic rocks (1465 Myr/1118 Myr). The variability in lithologic composition and age structure of individual countries reflects the complex tectonic makeup of this region that ranges from Precambrian cratons (e.g., northeast China and North Korea) to Mesozoic-Cenozoic active margins (e.g., Japan, the Philippines, Indonesia and New Guinea). The spatial resolution of the data varies from 44 km2 per polygon (Japan) to 1659 km2 per polygon (Taiwan) and is, on average (490 km2/polygon), similar to our previous analyses of the United States of America and Canada. The temporal and spatial resolution is sufficiently high to perform age-area analyses of individual river basins larger than ∼10,000 km2 and to quantitatively evaluate the relationship between bedrock geology and river chemistry. As many rivers draining tropical, mountainous islands of East and Southeast Asia have a disproportionate effect on the dissolved and particulate load delivered to the world oceans, bedrock geology in such river drainage basins disproportionately affect ocean chemistry.
    Description: Financial support was provided through the U.S. National Science Foundation (NSF-EAR-0125873) to BPE.
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    Hydrothermal venting at Vailulu'u Seamount : the smoking end of the Samoan chain (2006)
    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 Geochemistry Geophysics Geosystems 5 (2004): Q02003, doi:10.1029/2003GC000626.
    Description: The summit crater of Vailulu'u Seamount, the youngest volcano in the Samoan chain, hosts an active hydrothermal system with profound impact on the ocean water column inside and around its crater (2 km wide and 407 m deep at a 593 m summit depth). The turbidity of the ocean water reaches 1.4 NTU, values that are higher than in any other submarine hydrothermal system. The water is enriched in hydrothermal Mn (3.8 ppb) and 3He (1 × 10−11 cc/g) and we measured water temperature anomalies near the crater floor up to 0.2°C. The hydrothermal system shows complex interactions with the ocean currents around Vailulu'u that include tidally-modulated vertical motions of about 40–50 m, and replenishment of waters into the crater through breaches in the upper half of the crater wall. Inside and outside potential density gradients suggest that hydrothermal venting exports substantial amounts of water from the crater (1.3 ± 0.2 × 108 m3/day), which is in good agreement with fluxes obtained from a tracer release experiment inside the crater of Vailulu'u (0.8 × 108 m3/day [Hart et al., 2003]). This mass flux, in combination with the differences in the inside and outside crater temperature, yields a power output of around 760 megawatts, the equivalent of 20–100 MOR black smokers. The Mn output of 300 kg/day is approximately ten times the output of a single black smoker.
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    Composition and structure of the central Aleutian island arc from arc-parallel wide-angle seismic data (2006)
    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 Geochemistry Geophysics Geosystems 5 (2004): Q10006, doi:10.1029/2004GC000715.
    Description: New results from wide-angle seismic data collected parallel to the central Aleutian island arc require an intermediate to mafic composition for the middle crust and a mafic to ultramafic composition for the lower crust and yield lateral velocity variations that correspond to arc segmentation and trends in major element geochemistry. The 3-D ray tracing/2.5-D inversion of this sparse wide-angle data set, which incorporates independent phase interpretations and new constraints on shallow velocity structure, produces a faster and smoother result than a previously published velocity model. Middle-crustal velocities of 6.5–7.3 km/s over depths of ∼10–20 km indicate an andesitic to basaltic composition. High lower-crustal velocities of 7.3–7.7 km/s over depths of ∼20–35 km are interpreted as ultramafic-mafic cumulates and/or garnet granulites. The total crustal thickness is 35–37 km. This result indicates that the Aleutian island arc has higher velocities, and thus more mafic compositions, than average continental crust, implying that significant modifications would be required for this arc to be a suitable building block for continental crust. Lateral variations in average crustal velocity (below 10 km) roughly correspond to trends in major element geochemistry of primitive (Mg # 〉 0.6) lavas. The highest lower-crustal velocities (and presumably most mafic material) are detected in the center of an arc segment, between Unmak and Unalaska Islands, implying that arc segmentation exerts control over crustal composition.
    Description: Funding for this work was provided by the University of Wyoming Graduate School.
    Keywords: Continental crust ; Crustal geophysics ; Island arc ; Major element geochemistry
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    Upper crustal structure and axial topography at intermediate spreading ridges : seismic constraints from the southern Juan de Fuca Ridge (2006)
    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 Journal of Geophysical Research 110 (2005): B12104, doi:10.1029/2005JB003630.
    Description: We use multichannel seismic reflection data to image the upper crustal structure of 0-620 ka crust along the southern Juan de Fuca Ridge (JdFR). The study area comprises two segments spreading at intermediate rate with an axial high morphology with narrow (Cleft) and wide (Vance) axial summit grabens (ASG). Along most of the axis of both segments we image the top of an axial magma chamber (AMC). The AMC along Cleft deepens from south to north, from 2.0 km beneath the RIDGE Cleft Observatory and hydrothermal vents near the southern end of the segment, to 2.3 km at the northern end near the site of the 1980’s eruptive event. Along the Vance segment, the AMC also deepens from south to north, from 2.4 km to 2.7 km. Seismic layer 2A, interpreted as the basaltic extrusive layer, is 250-300 m thick at the ridge axis along the Cleft segment, and 300-350 m thick along the axis of the Vance segment. However off-axis layer 2A is similar in both segments (500-600 m), indicating ~90% and ~60% off-axis thickening at the Cleft and Vance segments, respectively. Half of the thickening occurs sharply at the walls of the ASG, with the remaining thickening occurring within 3-4 km of the ASG. Along the full length of both segments, layer 2A is thinner within the ASG, compared to the ridge flanks. Previous studies argued that the ASG is a cyclic feature formed by alternating periods of magmatism and tectonic extension. Our observations agree with the evolving nature of the ASG. However, we suggest that its evolution is related to large changes in axial morphology produced by small fluctuations in magma supply. Thus the ASG, rather than being formed by excess volcanism, is a rifted flexural axial high. The changes in axial morphology affect the distribution of lava flows along the ridge flanks, as indicated by the pattern of layer 2A thickness. The fluctuations in magma supply may occur at all spreading rates, but its effects on crustal structure and axial morphology are most pronounced along intermediate spreading rate ridges.
    Description: This study was supported by the National Science Foundation grants OCE-0002551 to Woods Hole Oceanographic Institution, OCE-0002488 to Lamont-Doherty Earth Observatory, and OCE-0002600 to Scripps Institution of Oceanography.
    Keywords: Mid-ocean ridge ; Juan de Fuca ; Crustal structure
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    Global temperature calibration of the alkenone unsaturation index (UK′37) in surface waters and comparison with surface sediments (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q02005, doi:10.1029/2005GC001054.
    Description: In this paper, we compile the current surface seawater C37 alkenone unsaturation (UK′37) measurements (n=629, −1 to 30°C temperature range) to derive a global, field-based calibration of UK′37 with alkenone production temperature. A single nonlinear “global” surface water calibration of UK′37 accurately predicts alkenone production temperatures over the diversity of modern-day oceanic environments and alkenone-synthesizing populations (T=−0.957 + 54.293(UK′37) − 52.894(UK′37)2 + 28.321(UK′37)3, r2=0.97, n=567). The mean standard error of estimation is 1.2°C with insignificant bias in estimated production temperature among the different ocean regions sampled. An exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients (e.g., the Brazil-Malvinas Confluence). In contrast to the surface water data, the calibration of UK′37 in surface sediments with overlying annual mean sea surface temperature (AnnO) is best fit by a linear model (AnnO=29.876(UK′37) − 1.334, r2=0.97, n=592). The standard error of estimation (1.1°C) is similar to that of the surface water production calibration, but a higher degree of bias is observed among the regional data sets. The sediment calibration differs significantly from the surface water calibration. UK′37 in surface sediments is consistently higher than that predicted from AnnO and the surface water production temperature calibration, and the magnitude of the offset increases as the surface water AnnO decreases. We apply the global production temperature calibration to the coretop UK′37 data to estimate the coretop alkenone integrated production temperature (coretop IPT) and compare this with the overlying annual mean sea surface temperature (AnnO). We use simple models to explore the possible causes of the deviation observed between the coretop temperature signal, as estimated by UK′37, and AnnO. Our results indicate that the deviation can best be explained if seasonality in production and/or thermocline production as well as differential degradation of 37:3 and 37:2 alkenones both affect the sedimentary alkenone signal.
    Description: C.R. acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG).
    Keywords: Alkenones ; Paleoproxies ; Sea surface temperature ; UK′37
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    Slope water, Gulf Stream, and seasonal influences on southern Mid-Atlantic Bight circulation during the fall-winter transition (2006)
    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 Journal of Geophysical Research 110 (2005): C02009, doi:10.1029/2004JC002311.
    Description: Observations from autumn, 2000, near the shelfbreak front in the Middle Atlantic Bight are used to describe the transition from stratified summer conditions to well-mixed winter conditions over the shelf. During the observational period, the front differed dramatically from climatological conditions, with buoyant Gulf Stream water found shoreward over the sub-surface shelfbreak front. Water mass analysis shows a large number of separate water masses with shelf, slope and Gulf Stream origins. The coolest shelf water was located at the shelfbreak and may be related to “cold pool” water masses observed to the north during summer. Shoreward of this shelfbreak water mass, a mid-shelf front was present which intersected the bottom at the 50 m isobath. High volume transports were associated with both the shelfbreak and mid-shelf fronts. Transport estimates from the cross-shelf sections were approximately 1 Sverdrup, which is large relative to previous estimates of shelf transport. The foot of the front was near the 130 m isobath, much deeper than the climatological position near the 75 m isobath, however this is consistent with a recent theory relating the magnitude of alongshelf transport to the depth at which the front intersects the bottom.
    Description: The authors gratefully acknowledge support from the Duke University - University of North Carolina Oceanographic Consortium for ship time aboard the R/V Cape Hatteras. MSL also gratefully acknowledges support from the Office of Naval Research (N00014-01-1-0260).
    Keywords: Shelfbreak front ; Mid-shelf front ; Shelf transport
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    A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations (2006)
    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 Paleoceanography 21 (2206): PA2002, doi:10.1029/2005PA001203.
    Description: We estimate tropical Atlantic upper ocean temperatures using oxygen isotope and Mg/Ca ratios in well-preserved planktonic foraminifera extracted from Albian through Santonian black shales recovered during Ocean Drilling Program Leg 207 (North Atlantic Demerara Rise). On the basis of a range of plausible assumptions regarding seawater composition at the time the data support temperatures between 33° and 42°C. In our low-resolution data set spanning ~84–100 Ma a local temperature maximum occurs in the late Turonian, and a possible minimum occurs in the mid to early late Cenomanian. The relation between single species foraminiferal δ18O and Mg/Ca suggests that the ratio of magnesium to calcium in the Turonian-Coniacian ocean may have been lower than in the Albian-Cenomanian ocean, perhaps coincident with an ocean 87Sr/86Sr minimum. The carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples. The δ13C values of phytane, combined with foraminiferal δ13C and inferred temperatures, were used to estimate atmospheric carbon dioxide concentrations through this interval. Estimates of atmospheric CO2 concentrations range between 600 and 2400 ppmv. Within the uncertainty in the various proxies, there is only a weak overall correspondence between higher (lower) tropical temperatures and more (less) atmospheric CO2. The GENESIS climate model underpredicts tropical Atlantic temperatures inferred from ODP Leg 207 foraminiferal δ18O and Mg/Ca when we specify approximate CO2 concentrations estimated from the biomarker isotopes in the same samples. Possible errors in the temperature and CO2 estimates and possible deficiencies in the model are discussed. The potential for and effects of substantially higher atmospheric methane during Cretaceous anoxic events, perhaps derived from high fluxes from the oxygen minimum zone, are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric CH4 concentrations. With 50 ppm CH4, GENESIS sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when CO2 concentrations specified to the model are near those inferred using the phytane δ13C proxy. However, atmospheric CO2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures.
    Description: Funding for this research was provided by the U.S. Science Support Program of the JOI, the Andrew W. Mellon Foundation Endowed Fund for Innovative Research, and Deutsche Forschungsgemeinschaft through the DFG-Research Center Ocean Margins.
    Keywords: Cretaceous ; Temperature ; Carbon dioxide
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    Radiocarbon constraint on relict organic carbon contributions to Ross Sea sediments (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q04012, doi:10.1029/2005GC001097.
    Description: We estimate the relative contribution of relict organic matter to the acid-insoluble organic carbon (AIOC) fraction of surface sediments from Ross Sea, Antarctica, on the basis of 14C abundance. The bulk isotopic characteristics of AIOC can largely be explained by simple two-source models of modern and relict organic carbon, when samples are grouped according to two geographical regions, namely, southwestern and south central Ross Sea. This spatial variability in relict organic carbon could be controlled by proximity to the edge of the Ross Ice Shelf and ice drainage areas. Radiocarbon abundance in the AIOC is potentially an excellent tool to estimate the contribution of relict organic carbon in the Antarctic margin sediments.
    Description: This work was partly supported by a grant from Japan Society for the Promotion of Science to N.O.
    Keywords: Ross Sea ; Radiocarbon ; Sediment ; Organic carbon
    Repository Name: Woods Hole Open Access Server
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    The Cleft revealed: geologic, magnetic, and morphologic evidence for construction of upper oceanic crust along the southern Juan de Fuca Ridge (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q04003, doi:10.1029/2005GC001038.
    Description: The geology and structure of the Cleft Segment of the Southern Juan de Fuca Ridge (JdFR) have been examined using high-resolution mapping systems, observations by remotely operated vehicle (ROV), ROV-mounted magnetometer, and the geochemical analysis of recovered lavas. Bathymetric mapping using multibeam (EM300) coupled with in situ observations that focused on near-axis and flank regions provides a detailed picture of 0 to 400 ka upper crust created at the southern terminus of the JdFR. A total of 53 rock cores and 276 precisely located rock or glass samples were collected during three cruises that included sixteen ROV dives. Our observations of the seafloor during these dives suggest that many of the unfaulted and extensive lava flows that comprise and/or cap the prominent ridges that flank the axial valley emanate from ridge parallel faults and fissures that formed in the highly tectonized zone that forms the walls of the axial valley. The geochemically evolved and heterogeneous nature of these near-axis and flank eruptions is consistent with an origin within the cooler distal edges of a crustal magma chamber or mush zone. In contrast, the most recent axial eruptions are more primitive (higher MgO), chemically homogeneous lobate, sheet, and massive flows that generate a distinct magnetic high over the axial valley. We suggest that the syntectonic capping volcanics observed off-axis were erupted from near-axis and flank fissures and created a thickened extrusive layer as suggested by the magnetic and seismic data. This model suggests that many of the lavas that comprise the elevated ridges that bound the axial valley of the Cleft Segment were erupted during the collapse of a magmatic cycle not during the robust phase that established a new magmatic cycle.
    Description: This research has been partially supported by a NSF grant to M. Perfit (OCE-0221541). M. Tivey acknowledges support from WHOI’s Mellon grant for Independent Study. Support for D. Stakes, T. Ramirez, D. Caress, and N. Maher and for the entire field program was provided by funds to MBARI from the Lucille and David Packard Foundation.
    Keywords: Basalt ; Ridge
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    Detachment shear zone of the Atlantis Massif core complex, Mid-Atlantic Ridge, 30°N (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q06016, doi:10.1029/2005GC001109.
    Description: Near-bottom investigations of the cross section of the Atlantis Massif exposed in a major tectonic escarpment provide an unprecedented view of the internal structure of the footwall domain of this oceanic core complex. Integrated direct observations, sampling, photogeology, and imaging define a mylonitic, low-angle detachment shear zone (DSZ) along the crest of the massif. The shear zone may project beneath the nearby, corrugated upper surface of the massif. The DSZ and related structures are inferred to be responsible for the unroofing of upper mantle peridotites and lower crustal gabbroic rocks by extreme, localized tectonic extension during seafloor spreading over the past 2 m.y. The DSZ is characterized by strongly foliated to mylonitic serpentinites and talc-amphibole schists. It is about 100 m thick and can be traced continuously for at least 3 km in the tectonic transport direction. The DSZ foliation arches over the top of the massif in a convex-upward trajectory mimicking the morphology of the top of the massif. Kinematic indicators show consistent top-to-east (toward the MAR axis) tectonic transport directions. Foliated DSZ rocks grade structurally downward into more massive basement rocks that lack a pervasive outcrop-scale foliation. The DSZ and underlying basement rocks are cut by discrete, anastomosing, normal-slip, shear zones. Widely spaced, steeply dipping, normal faults cut all the older structures and localize serpentinization-driven hydrothermal outflow at the Lost City Hydrothermal Field. A thin (few meters) sequence of sedimentary breccias grading upward into pelagic limestones directly overlies the DSZ and may record a history of progressive rotation of the shear zone from a moderately dipping attitude into its present, gently dipping orientation during lateral spreading and uplift.
    Description: This work was supported by NSF grants OCE-9712430 and 0136816 to Karson and Kelley and Swiss SNF grant 2100-068055 to Früh-Green.
    Keywords: Detachment faults ; Faults ; Oceanic core complex ; Seafloor spreading ; Serpentinite ; Shear zones
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    Bottom boundary layer flow and salt injection from the continental shelf to slope (2006)
    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): L13608, doi:10.1029/2006GL026311.
    Description: Austral winter oceanographic measurements from the northwest Australian continental shelf reveal salty water forming evaporatively inshore, moving across the wide shelf near the bottom and into the adjacent open ocean when the shelf edge alongshore flow is equatorward. The salt tongue is absent during more normal conditions, when the poleward Leeuwin Current is present. We hypothesize that the flow reversal enables shelf-wide bottom boundary layer (Ekman) transport and thus creates the shelf-edge convergence that accounts for the observed salt tongue. This flow is absent under sustained normal conditions because of buoyancy arrest in the bottom boundary layer.
    Description: This research was supported by the Processes and Prediction Division (Code 322 PO) of the U.S. Office of Naval Research through grant N00014-02-1-0767.
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    Interannual variability of the South China Sea throughflow inferred from wind data and an ocean data assimilation product (2006)
    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): L14605, doi:10.1029/2006GL026316.
    Description: The Luzon Strait transport, as an index for the South China Sea throughflow, has attracted much attention. In this study the interannual variability of the Luzon Strait transport is examined, using the Island Rule and results from an ocean general circulation model. Transport variability obtained from these two approaches are consistent with each other. Assessment of contribution from each integral segment involved in the Island Rule indicates that wind stress in the western and central equatorial Pacific is the key factor regulating the interannual variability of the Luzon Strait transport, whereas the effect of local wind stress in the vicinity of the Luzon Strait is secondary. Analysis also shows that when the westerly (easterly) wind anomalies in the tropical Pacific break out, the Luzon Strait transport increases (decreases), consistent with the variations in the North Equatorial Current during El Niño (La Niña) events.
    Description: This research was supported by NSF of China (Grants Nos. 40136010 and 40406006). YD and TQ were supported by the National Aeronautics and Space Administration through grant NAG5-12756, and TQ also supported by Japan Agency for Marine-Earth Science and Technology through its sponsorship of the International Pacific Research Center.
    Keywords: Island Rule ; Wind stress ; South China Sea throughflow
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    Heat flow variations on a slowly accreting ridge : constraints on the hydrothermal and conductive cooling for the Lucky Strike segment (Mid-Atlantic Ridge, 37°N) (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q07011, doi:10.1029/2005GC001178.
    Description: We report 157 closely spaced heat flow measurements along the Lucky Strike segment in the Mid-Atlantic Ridge (MAR) for ages of the ocean floor between 0 and 11 Ma. On the eastern flank of a volcanic plateau delimiting off-axis and axial domains, the magnitude of heat flow either conforms to the predictions of conductive lithospheric cooling models or is affected by localized anomalies. On the western flank it is uniformly lower than conductive model predictions. We interpret the observed patterns of heat flow by lateral fluid circulation in a highly permeable oceanic basement. The circulation geometries are probably 3-D rather than 2-D and are determined by the configuration of the basement/sediment interface and the distribution of effectively unsedimented seamounts where water recharge can occur. Two major hydrothermal circulation systems can possibly explain the observations off-axis: the first would involve lateral pore water flow from west to east, and the second would have a reverse flow direction. The wavelengths and magnitudes of heat flow anomalies require Darcy velocities of the order of 1–4 m/year, which are similar to those proposed for fast-accreted crust elsewhere. However, a large proportion of this MAR domain remains unaffected by hydrothermal cooling, which is a relatively unusual observation but confirms the validity of conductive thermal models for seafloor ages between 5 and 10 Ma. Closer to the ridge axis (〈5 Myr old crust), water circulation affects the overall axial domain, as larger proportions of basement are exposed. As much as 80–90% of the heat flux from the axial domain may be transferred to the Lucky Strike vent field, in agreement with the estimated discharge.
    Keywords: Heat flow ; Mid-Atlantic Ridge
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    Meridional circulation during the Last Glacial Maximum explored through a combination of South Atlantic δ18O observations and a geostrophic inverse model (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q11N07, doi:10.1029/2006GC001383.
    Description: The vertical profile of meridional transport in the South Atlantic is examined by combining paleoceanographic observations with a geostrophic circulation model using an inverse method. δ18Ocalcite observations along the margins of the South Atlantic show that upper-ocean cross-basin differences were weaker during the Last Glacial Maximum (LGM) than the Holocene. The δ18Ocalcite observations can be explained by a shift of water-mass properties without any change in the overturning circulation. Alternatively, they may indicate a reduced LGM cross-basin density difference and, via the thermal wind relation, a reduced vertical shear. Model inversions of δ18Ocalcite are found to require meridional transports different from the modern only after three assumptions are made: temperature and salinity distributions are spatially smooth, the relationship between salinity and δ18Owater is linear and spatially invariant, and LGM temperatures are known to within 1°C along the margins. The last assumption is necessary because an independent constraint on temperature or salinity is required to determine density from δ18Ocalcite observations. δ18Ocalcite observations are clearly useful, but before any firm constraints can be placed on LGM meridional transport, it appears necessary to better determine the relationship between δ18Ocalcite and density.
    Description: P.H. was funded by the NOAA postdoctoral program in climate and global change, and G.G. was partially funded by NSF paleoclimate program ATM-0502482.
    Keywords: Inverse modeling ; Last Glacial Maximum ; Meridional ocean circulation ; Geostrophy
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    Submarine volcanic morphology of the western Galapagos based on EM300 bathymetry and MR1 side-scan sonar (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q03010, doi:10.1029/2006GC001464.
    Description: A compilation of high-resolution EM300 multibeam bathymetric and existing MR1 side-scan sonar data was used to investigate the volcanic morphology of the flanks of the western Galápagos Islands. The data portray an assortment of constructional volcanic features on the shallow to deep submarine flanks of Fernandina, Isabela, and Santiago Islands, including rift zones and groups of cones that are considered to be the primary elements in constructing the archipelagic apron. Ten submarine rift zones were mapped, ranging in length from 5 to 20 km, comparable in length to western Canary Island rift zones but significantly shorter than Hawaiian submarine rift zones. A detailed analysis of the northwestern Fernandina submarine rift, including calculated magnetization from a surface-towed magnetic study, suggests that the most recent volcanism has focused at the shallow end of the rift. Small submarine volcanic cones with various morphologies (e.g., pointed, cratered, and occasionally breached) are common in the submarine western Galápagos both on rift zones and on the island flanks where no rifts are present. At depths greater than ∼3000 m, large lava flow fields in regions of low bathymetric relief have been previously identified as a common seafloor feature in the western Galápagos by Geist et al. (2006); however, their source(s) remained enigmatic. The new EM300 data show that a number of the deep lava flows originate from small cones along the mid-lower portion of the NW submarine rift of Fernandina, suggesting that the deep flows owe their origin, at least in part, to submarine rift zone volcanism.
    Description: Data collected on TN188 was funded by NSF grant OCE0326148 and NOAA grant NA04OAR460009 to S.M.W. Support for data collected on previous multibeam and MR1 cruises was provided by NSF grants OCE9811504 and OCE0002461 (D.J.F.).
    Keywords: Galapagos Islands ; EM300 multibeam bathymetry ; MR1 side-scan sonar ; Submarine volcanic cones ; Submarine volcanic rift zones ; Deep lava flows
    Repository Name: Woods Hole Open Access Server
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    Insights on coccolith chemistry from a new ion probe method for analysis of individually picked coccoliths (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06020, doi:10.1029/2006GC001546.
    Description: The elemental chemistry of calcareous nannofossils may provide valuable information on past ocean conditions and coccolithophorid physiology, but artifacts from noncoccolith particles and from changing nannofossil assemblages may bias geochemical records from coccolith size fractions. We describe the first method for picking individual coccoliths using a tungsten needle in micromanipulator. Epoxy-mounted individuals and populations of coccoliths can be analyzed by secondary ion mass spectrometry (SIMS). For Paleocene sediments the technique distinguishes the high Sr/Ca ratios of coccoliths (0.3 to 2.8 mmol/mol) from low ratios in abiogenic calcite blades (0.1 mmol/mol). The large heterogeneity of Sr/Ca ratios among different genera suggests that primary geochemical differences have not been homogenized by diagenetic overgrowth and the thick massive coccoliths of the late Paleocene are a primary feature of biomineralization. Sr/Ca ratios for modern genera are on average higher than those of Paleogene genera but exhibit a comparable level of variability.
    Description: Research supported by NSF OCE-0424474 to H. Stoll and a fellowship to H. Stoll from the Spanish Ministry of Education cofunded by the European Social Fund.
    Keywords: Ion probe ; SIMS ; Sr/Ca ; Coccolith
    Repository Name: Woods Hole Open Access Server
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    Quantitative bedrock geology of the continents and large-scale drainage regions (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06009, doi:10.1029/2006GC001544.
    Description: We quantitatively analyze the area-age distribution of sedimentary, extrusive volcanic, and endogenous (plutonic and/or metamorphic) bedrock on the basis of data from the most recent digital Geological Map of the World at a scale of 1:25,000,000. The spatial resolution of the digital bedrock data averages 13,905 km2 per polygon. Comparison of certain regions of the world, previously analyzed at higher spatial resolution, with the low-resolution world data reveals general consistency in the areal exposure of major rock types as well as a minor systematic bias toward older average bedrock ages in the global data set. Application of the global bedrock data to 19 large-scale drainage regions and three large, internally drained regions reveals considerable regional variability of Earth's bedrock geology that is consistent with the dominant geotectonic setting of the respective drainage region.
    Description: B.P.E. acknowledges financial support from the United States National Science Foundation (NSF-EAR- 0125873) and from the Woods Hole Oceanographic Institution.
    Keywords: Geologic map ; World ; Age ; Bedrock ; Sediment ; Volcanic rock
    Repository Name: Woods Hole Open Access Server
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  • 79
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    Evolution of the Southwest Indian Ridge from 55°45′E to 62°E : changes in plate-boundary geometry since 26 Ma (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06022, doi:10.1029/2006GC001559.
    Description: From 55°45′E to 58°45′E and from 60°30′E to 62°00′E, the ultraslow-spreading Southwest Indian Ridge (SWIR) consists of magmatic spreading segments separated by oblique amagmatic spreading segments, transform faults, and nontransform discontinuities. Off-axis magnetic and multibeam bathymetric data permit investigation of the evolution of this part of the SWIR. Individual magmatic segments show varying magnitudes and directions of asymmetric spreading, which requires that the shape of the plate boundary has changed significantly over time. In particular, since 26 Ma the Atlantis II transform fault grew by 90 km to reach 199 km, while a 45-km-long transform fault at 56°30′E shrank to become an 11 km offset nontransform discontinuity. Conversely, an oblique amagmatic segment at the center of a first-order spreading segment shows little change in orientation with time. These changes are consistent with the clockwise rotation of two ~450-km-wide first-order spreading segments between the Gallieni and Melville transform faults (52–60°E) to become more orthogonal to spreading. We suggest that suborthogonal first-order spreading segments reflect a stable configuration for mid-ocean ridges that maximizes upwelling rates in the asthenospheric mantle and results in a hotter and weaker ridge-axis that can more easily accommodate seafloor spreading.
    Description: Funding for this work came from a JOI-Schlanger Fellowship to Baines and NSF grant 0352054 to Cheadle and John.
    Keywords: Southwest Indian Ridge ; Atlantis II fracture zone ; Asymmetric spreading ; Ridge segmentation
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  • 80
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    Sea surface temperature signatures of oceanic internal waves in low winds (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C06014, doi:10.1029/2006JC003947.
    Description: In aerial surveys conducted during the Tropical Ocean–Global Atmosphere Coupled Ocean-Atmosphere Response Experiment and the low-wind component of the Coupled Boundary Layer Air-Sea Transfer (CBLAST-Low) oceanographic field programs, sea surface temperature (SST) variability at relatively short spatial scales (O(50 m) to O(1 km)) was observed to increase with decreasing wind speed. A unique set of coincident surface and subsurface oceanic temperature measurements from CBLAST-Low is used to investigate the subsurface expression of this spatially organized SST variability, and the SST variability is linked to internal waves. The data are used to test two previously hypothesized mechanisms for SST signatures of oceanic internal waves: a modulation of the cool-skin effect and a modulation of vertical mixing within the diurnal warm layer. Under conditions of weak winds and strong insolation (which favor formation of a diurnal warm layer), the data reveal a link between the spatially periodic SST fluctuations and subsurface temperature and velocity fluctuations associated with oceanic internal waves, suggesting that some mechanism involving the diurnal warm layer is responsible for the observed signal. Internal-wave signals in skin temperature very closely resemble temperature signals measured at a depth of about 20 cm, indicating that the observed internal-wave SST signal is not a result of modulation of the cool-skin effect. Numerical experiments using a one-dimensional upper ocean model support the notion that internal-wave heaving of the warm-layer base can produce alternating bands of relatively warm and cool SST through the combined effects of surface heating and modulation of wind-driven vertical shear.
    Description: We gratefully acknowledge funding for this research from the Office of Naval Research through the CBLAST Departmental Research Initiative (grants N00014-01-1-0029, N00014-05-10090, N00014-01-1-0081, N00014-04-1-0110, N00014-05-1-0036, N00014-01-1-0080) and the Secretary of the Navy/Chief of Naval Operations Chair (grant N00014-99-1-0090).
    Keywords: Internal waves ; Upper-ocean processes
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  • 81
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    Nonvolcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15°N on the Mid-Atlantic Ridge : a structural synthesis of ODP Leg 209 (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. 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 8 (2007): Q06015, doi:10.1029/2006GC001567.
    Description: Drilling during ODP Leg 209, dredging, and submersible dives have delineated an anomalous stretch of the Mid-Atlantic Ridge north and south of the 15°20′N Fracture Zone. The seafloor here consists dominantly of mantle peridotite with gabbroic intrusions that in places is covered by a thin, discontinuous extrusive volcanic layer. Thick lithosphere (10–20 km) in this region inhibits magma from reaching shallow levels beneath the ridge axis, thereby causing plate accretion to be accommodated by extensional faulting rather than magmatism. The bathymetry and complex fault relations in the drill-core suggest that mantle denudation and spreading are accommodated by a combination of high-displacement, rolling-hinge normal faults and secondary lower-displacement normal faults. These extensional faults must also accommodate corner flow rotation (up to 90°) of the upwelling mantle within the shallow lithosphere, consistent with remnant magnetic inclinations in denuded peridotite and gabbro from Leg 209 core that indicate up to 90° of sub-Curie-temperature rotation.
    Description: This work was funded by a grant from the Joint Oceanographic Institutions.
    Keywords: Seafloor spreading ; Ocean Drilling Program ; Nonvolcanic mid-ocean ridges ; Extensional faulting
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    Spatial variability of mixing in the Southern Ocean (2006)
    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): L18603, doi:10.1029/2005GL023568.
    Description: Strain variance from standard hydrographic profiles in the southern hemisphere oceans shows that turbulent mixing is vertically and spatially non-uniform. In the South Atlantic, Indian and South Pacific Oceans, enhanced diffusivities are found over rough topography. Consistent with internal tide generated mixing, the water column diffusivity returns to background levels 500 m to 1000 m off the sea floor. In the Southern Ocean, enhanced diffusivities throughout the entire water column below 1500 m are found in the Antarctic Circumpolar Current over complex topography. Differences in the vertical extent of enhanced diffusivity profiles in the Antarctic Circumpolar Current between the parameterizations based on tidal models and topography and of the present estimate of strain variance imply that elevated vertical diffusivity profiles in the Southern Ocean are due to the interaction between the mean geostrophic current and bottom topography.
    Description: BMS was supported by the Ocean and Climate Change Institute at the Woods Hole Oceanographic Institution.
    Keywords: Fine structure and microstructure ; Internal and inertial waves ; Turbulence, diffusion, and mixing processes
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    Extending the record of photosynthetic activity in the eastern United States into the presatellite period using surface diurnal temperature range (2006)
    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): L08405, doi:10.1029/2005GL022583.
    Description: In this study, we demonstrate that mid-latitude surface measurements of diurnal temperature range (DTR) can be used to reconstruct decadal variability of regional-scale terrestrial photosynthetic activity 1) during and prior to the period with satellite retrievals of land greenness and 2) without the need for moisture data. While the two relative maxima present in the seasonal evolution of DTR can determine the beginning and the end of the growing season, the summertime average DTR can be used as a proxy of summertime terrestrial photosynthesis. In a case study in the eastern United States (1966–1997), the DTR reconstructions indicate significant natural decadal variability in photosynthetic activity, but no secular, long-term trend. The summertime photosynthesis was found to be controlled primarily by moisture availability. Also, contrary to existing model parameterizations, the timing of spring onset was found to depend on both temperature and moisture.
    Description: This work is supported by National Science Foundation grant ATM-9987457, NASA EOS-IDS grants NAG5-9514 and NNG04GK34G, NASA Carbon Cycle Program grant NAG5-11200, and the WHOI Ocean and Climate Change Institute.
    Keywords: Biogeochemical cycles, processes, and modeling ; Water cycles ; Evapotranspiration ; Land/atmosphere interactions ; North America
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    Reflection and tunneling of ocean waves observed at a submarine canyon (2006)
    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): L10602, doi:10.1029/2005GL022834.
    Description: Ocean surface gravity waves with periods between 20 and 200 s were observed to reflect from a steep-walled submarine canyon. Observations of pressure and velocity on each side of the canyon were decomposed into incident waves arriving from distant sources, waves reflected by the canyon, and waves transmitted across the canyon. The observed reflection is consistent with longwave theory, and distinguishes between cases of normal and oblique angles of incidence. As much as 60% of the energy of waves approaching the canyon normal to its axis was reflected, except for waves twice as long as the canyon width, which were transmitted across with no reflection. Although waves approaching the canyon at oblique angles cannot propagate over the canyon, total reflection was observed only at frequencies higher than 20 mHz, with lower frequency energy partially transmitted across, analogous to the quantum tunneling of a free particle through a classically impenetrable barrier.
    Description: Funding was provided by the Office of Naval Research and the National Science Foundation.
    Keywords: Wave reflection ; Infragravity ; Submarine canyon
    Repository Name: Woods Hole Open Access Server
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  • 85
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    Seawater-peridotite interactions : first insights from ODP Leg 209, MAR 15°N (2006)
    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 Geochemistry Geophysics Geosystems 5 (2004): Q09F26, doi:10.1029/2004GC000744.
    Description: We present first results of a petrographic study of hydrothermally altered peridotites drilled during Ocean Drilling Program (ODP) Leg 209 in the 15°20′N fracture Zone area on the Mid-Atlantic Ridge (MAR). We find that serpentinization is extensive at all drill sites. Where serpentinization is incomplete, phase relations indicate two major reaction pathways. One is reaction of pyroxene to talc and tremolite, and the other is reaction of olivine to serpentine, magnetite, and brucite. We interpret these reactions in the light of recent peridotite-seawater reaction experiments and compositions of fluids venting from peridotite massifs at a range of temperatures. We suggest that the replacement of pyroxene by talc and tremolite takes place at temperatures 〉350°–400°C, where olivine is stable. The breakdown of olivine to serpentine, magnetite, and brucite is favored at temperatures below 250°C, where olivine reacts faster then pyroxene. High-temperature hydrothermal fluids venting at the Logatchev and Rainbow sites are consistent with rapid reaction of pyroxene and little or no reaction of olivine. Moderate-temperature fluids venting at the Lost City site are consistent with ongoing reaction of olivine to serpentine and brucite. Many completely serpentinized peridotites lack brucite and talc because once the more rapidly reacting phase is exhausted, interaction with the residual phase will change fluid pH and silica activity such that brucite or talc react to serpentine. At two sites we see strong evidence for continued fluid flow and fluid-rock interaction after serpentinization was complete. At Site 1268, serpentinites underwent massive replacement by talc under static conditions. This reaction requires either removal of Mg from or addition of Si to the system. We propose that the talc-altered rocks are Si-metasomatized and that the source of Si is likely gabbro-seawater reaction or breakdown of pyroxene deeper in the basement. The basement at Site 1268 is heavily veined, with talc and talc-oxide-sulfide veins being the most common vein types. It appears that the systems evolved from reducing (oxygen fugacity buffered by magnetite-pyrrhotite-pyrite and lower) to oxidizing (dominantly hematite). We propose that this transition is indicative of high fluid flux under retrograde conditions and that the abundance of hematite may relate to the Ca-depleted nature of the basement that prevents near-quantitative removal of seawater sulfate by anhydrite precipitation. At site 1272 we find abundant iowaite partly replacing brucite. While this is the first report of iowaite from a mid-ocean ridge setting, its presence indicates, again, fairly oxidizing conditions. Our preliminary results indicate that peridotite-seawater and serpentinite-seawater interactions can take place under a wider range of temperature and redox conditions than previously appreciated.
    Description: This research used data and/or samples supplied by the Ocean Drilling Program (ODP). ODP is sponsored by the U.S. National Science Foundation (NSF) and participating countries under management of Joint Oceanographic Institutions (JOI), Inc.
    Keywords: Hydrothermal system ; Ocean Drilling Program ; Oceanic crust ; Serpentinite ; Water-rock interaction
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    Long nonlinear internal waves (2006)
    Annual Reviews
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Annual Reviews, 2006. This article is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Fluid Mechanics 38 (2006): 395-425, doi:10.1146/annurev.fluid.38.050304.092129.
    Description: Over the past four decades, the combination of in situ and remote sensing observations has demonstrated that long nonlinear internal solitary-like waves are ubiquitous features of coastal oceans. The following provides an overview of the properties of steady internal solitary waves and the transient processes of wave generation and evolution, primarily from the point of view of weakly nonlinear theory, of which the Korteweg-de Vries equation is the most frequently used example. However, the oceanographically important processes of wave instability and breaking, generally inaccessible with these models, are also discussed. Furthermore, observations often show strongly nonlinear waves whose properties can only be explained with fully nonlinear models.
    Description: KRH acknowledges support from NSF and ONR and an Independent Study Award from the Woods Hole Oceanographic Institution. WKM acknowledges support from NSF and ONR, which has made his work in this area possible, in close collaboration with former graduate students at Scripps Institution of Oceanography and MIT.
    Keywords: Solitary waves ; Nonlinear waves ; Stratified flow ; Physical Oceanography
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  • 87
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    Near-surface ocean temperature (2006)
    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 Journal of Geophysical Research 111 (2006): C02004, doi:10.1029/2004JC002689.
    Description: The first open ocean deployment of the Skin Depth Experimental Profiler (SkinDeEP) was from the R/V Melville in the Gulf of California during the Marine Optical Characterization Experiment (MOCE–5). SkinDeEP is an autonomous, vertical profiler for the upper few meters of the ocean. During MOCE–5, SkinDeEP was deployed on 10 separate occasions, and profiles were made at intervals of approximately one minute each. A total of 976 profiles were acquired during the cruise. The ocean skin temperatures were measured by the Marine Atmosphere Emitted Radiance Interferometer (M–AERI), an infrared spectroradiometer. Typical meteorological conditions were of low winds and high insolation. The dataset provided captures the near-surface temperature structure that decouples the skin layer from the conventional in–situ bulk sea surface temperature measurements made at a depth of a few meters. Data from SkinDeEP showed strong diurnal warming within the upper few meters, with one extreme case of 4.6 K. There were large discrepancies when computing the skin–bulk temperature difference with bulk temperatures at different depths. Results also show the strong dependency of estimating air–sea heat flux based on SST, with warm–layer errors of almost 60 Wm-2 associated with intense stratification. This indicates the importance of the inclusion of the skin temperature for accurate calculation of latent, sensible, and net longwave heat fluxes.
    Description: The development of SkinDeEP was funded through the Research Council of Norway (Prosjektnr. 127872/720). Support was provided by the European Commission under the Marie Curie Fellowship contract ERBFMBICT983162. Further supportwas provided by NSF grant OCE–0241834 and National Oceanographic Partnership Program Award No. NNG04GM56G.
    Keywords: Air-sea heat flux ; Cool skin ; Warm layer
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    Effect of historical changes in land use and climate on the water budget of an urbanizing watershed (2006)
    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 Water Resources Research 42 (2006): W03426, doi:10.1029/2005WR004131.
    Description: We assessed the effects of historical (1931-1998) changes in both land-use and climate on the water budget of a rapidly urbanizing watershed, Ipswich River basin (IRB), in northeastern Massachusetts. Water diversions and extremely low flow during summer are major issues in the IRB. Our study centers on a detailed analysis of diversions and a combined empirical/modeling treatment of evapotranspiration (ET) response to changes in climate and land-use. A detailed accounting of diversions showed that net diversions increased due to increases in water withdrawals (primarily ground water pumping) and export of sewage. Net diversions constitute a major component of runoff (20% of streamflow). Using a combination of empirical analysis and physically based modeling we related an increase in precipitation (2.7 mm/yr) and changes in other climate variables to an increase in ET (1.7 mm/yr). Simulations with a physically based water-balance model showed that the increase in ET could be attributed entirely to a change in climate, while the effect of land-use change was negligible. The land-use change effect was different from ET and runoff trends commonly associated with urbanization. We generalized these and other findings to predict future streamflow using climate change scenarios. Our study could serve as a framework for studying suburban watersheds, being the first study of a suburban watershed that addresses long-term effects of changes in both land-use and climate, and accounts for diversions and other unique aspects of suburban hydrology.
    Description: This research was partially supported by NSF grants (DEB-9726862, OCE-9726921 and OCE-0423565).
    Keywords: Water budgets ; Evapotranspiration ; Climate change ; Land-use change ; Urbanization ; Water-balance model ; Ipswich River
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    An estimate of the cross-frontal transport at the shelf break of the East China Sea with the Finite Volume Coastal Ocean Model (2006)
    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 Journal of Geophysical Research 111 (2006): C03012, doi:10.1029/2005JC003290.
    Description: The Finite Volume Coastal Ocean Model (FVCOM) is used to estimate the onshore cross-frontal transport at the shelf break of the East China Sea. Boundary conditions of FVCOM are provided by the Princeton Ocean Model simulating ocean currents in the Yellow Sea and East China Sea realistically. One advantage of this study is that the unstructured triangular cell grid of FVCOM resolves complex bottom topography that may trigger Kuroshio frontal waves. It is anticipated that these nonlinear frontal waves enhance the exchange of seawater between the Kuroshio and shelf regions. Kuroshio frontal waves in the model are excited around the location where the bottom slope changes abruptly, and have the phase speed and amplitude consistent with those observed in the East China Sea. In addition, the model reproduces the onshore transport associated with growing frontal waves in the upper and lower layers. On the basis of passive tracer experiments, the annually averaged onshore-transport integrated along the shelf break is estimated to be 0.85 × 106 m3/s.
    Description: This study was carried out when A. I. stayed at WHOI with the grant of Overseas Advanced Educational Research Practice Support Program supported by the Ministry of Education, Science and Culture, Japan. In addition, the Japan Society for the Promotion of Science supported this study through Grant-in-Aid for Scientific Research.
    Keywords: East China Sea ; Kuroshio frontal wave ; Cross-frontal transport ; FVCOM
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    Primary U distribution in scleractinian corals and its implications for U series dating (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q05022, doi:10.1029/2005GC001138.
    Description: In this study we use microsampling techniques to explore diagenetic processes in carbonates. These processes are important as they can affect the accuracy of U series chronometry. Fission track maps of deep-sea scleractinian corals show a threefold difference between the minimum and maximum [U] in modern corals, which is reduced to a factor of 2 in fossil corals. We use micromilling and MC-ICP-MS to make detailed analyses of the [U] and δ234Uinitial distributions in corals from 218 ka to modern. Within each fossil coral we observe a large range of δ234Uinitial values, with high δ234Uinitial values typically associated with low [U]. A simple model shows that this observation is best explained by preferential movement of alpha-decay produced 234U atoms (alpha-recoil diffusion). Open-system addition of 234U may occur when alpha-recoil diffusion is coupled with a high [U] surface layer, such as organic material. This process can result in large, whole-coral δ234Uinitial elevations with little effect on the final age. The diagenetic pathways that we model are relevant to both shallow-water and deep-sea scleractinian corals since both exhibit primary [U] heterogeneity and may be subject to U addition.
    Description: We gratefully acknowledge The Comer Foundation for Abrupt Climate Change.
    Keywords: Uranium ; Diagenesis ; Coral ; Dating
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    Paleointensity applications to timing and extent of eruptive activity, 9°–10°N East Pacific Rise (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q06006, doi:10.1029/2005GC001141.
    Description: Placing accurate age constraints on near-axis lava flows has become increasingly important given the structural and volcanic complexity of the neovolcanic zone at fast spreading ridges. Geomagnetic paleointensity of submarine basaltic glass (SBG) holds promise for placing quantitative age constraints on near-axis flows. In one of the first extensive tests of paleointensity as a dating tool or temporal marker we present the results of over 550 successful SBG paleointensity estimates from 189 near-axis (〈4 km) sites at the East Pacific Rise, 9°–10°N. Paleointensities range from 6 to 53 μT and spatially correspond to the pattern expected from known temporal variations in the geomagnetic field. Samples within and adjacent to the axial summit trough (AST) have values approximately equal to or slightly higher than the present-day. Samples out to 1–3 km from the AST have values higher than the present-day, and samples farther off axis have values lower than the present-day. The on-axis samples (〈500 m from the AST) provide a test case for using models of paleofield variation for the past few hundred years as an absolute dating technique. Results from samples collected near a well-documented eruption in 1991–1992 suggest there may be a small negative bias in the paleointensity estimates, limiting resolution of the dating technique. Possible explanations for such a bias include local field anomalies produced by preexisting magnetic terrain; anomalously high magnetic unblocking temperatures, leading to a small cooling rate bias; and/or the possibility of a chemical remanence produced by in situ alteration of samples likely to have complicated thermal histories. Paleointensity remains useful in approximating age differences in young flows, and a clear along-axis paleointensity contrast near 9°50′N is suggestive of a ∼150–200 year age difference. Paleointensity values of off-axis samples are generally consistent with rough age interpretations based on side scan data. Furthermore, spatial patterns in the paleointensity suggest extensive off-axis flow emplacement may occur infrequently, with recurrence intervals of 10–20 kyr. Results of a stochastic model of lava emplacement show that this can be achieved with a single distribution of flows, with flow size linked to time between eruptions.
    Description: This work was accomplished with support from NSF grants OCE-0095698 (J. S. G.), OCE-0095342 (D. V. K.), OCE-9912072 (M. R. P.), OCE-0138088 (M. R. P.), and OCE-9819261 (D. J. F.).
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    A pan-arctic evaluation of changes in river discharge during the latter half of the 20th century (2006)
    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): L06715, doi:10.1029/2006GL025753.
    Description: Several recent publications have documented changes in river discharge from arctic and subarctic watersheds. Comparison of these findings, however, has been hampered by differences in time periods and methods of analysis. Here we compare changes in discharge from different regions of the pan-arctic watershed using identical time periods and analytical methods. Discharge to the Arctic Ocean increased by 5.6 km3/y/y during 1964-2000, the net result of a large increase from Eurasia moderated by a small decrease from North America. In contrast, discharge to Hudson/James/Ungava Bays decreased by 2.5 km3/y/y during 1964-2000. While this evaluation identifies an overall increase in discharge (~120 km3/y greater discharge at the end of the time period as compared to the beginning for Hudson/James/Unvaga Bays and the Arctic Ocean combined), the contrasting regional trends also highlight the need to understand the consequences of adding/removing freshwater from particular regions of the arctic and subarctic oceans.
    Description: This work was supported by the Arctic System Science Program of the National Science Foundation (NSF-OPP-0229302, NSF-OPP-0230211, NSF-OPP-0519840) and by the National Oceanic and Atmospheric Administration (NA17RJ2612).
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    Sea surface temperature pattern reconstructions in the Arabian Sea (2006)
    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 Paleoceanography 21 (2006): PA1014, doi:10.1029/2005PA001162.
    Description: Sea surface temperature (SST) and seawater δ18O (δ18Ow) were reconstructed in a suite of sediment cores from throughout the Arabian Sea for four distinct time intervals (0 ka, 8 ka, 15 ka, and 20 ka) with the aim of understanding the history of the Indian Monsoon and the climate of the Arabian Sea region. This was accomplished through the use of paired Mg/Ca and δ18O measurements of the planktonic foraminifer Globigerinoides ruber. By analyzing basin-wide changes and changes in cross-basinal gradients, we assess both monsoonal and regional-scale climate changes. SST was colder than present for the majority of sites within all three paleotime slices. Furthermore, both the Indian Monsoon and the regional Arabian Sea mean climate have varied substantially over the past 20 kyr. The 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2.5°–3.5°C attributable, in part, to the influences of glacial atmospheric CO2 concentrations and large continental ice sheets. The elimination of the cross-basinal SST gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength. Changes in δ18Ow that are smaller than the δ18O signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing. SSTs throughout the Arabian Sea were still cooler than present by an average of 1.4°C in the 8 ka time slice. These cool SSTs, along with lower δ18Ow throughout the basin, are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation. The results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling.
    Description: Analyses were funded by a SGER grant from the NSF (OCE03–34598). Funding was also provided by a Schlanger Ocean Drilling Program Fellowship (to K.A.D.) and NSF Grant OCE02–20776 (to D.W.O.). 16
    Keywords: Arabian Sea ; Mg/Ca ; Indian monsoon
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    Effects of wave rollers and bottom stress on wave setup (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C02003, doi:10.1029/2006JC003549.
    Description: Setup, the increase in the mean water level associated with breaking waves, observed between the shoreline and about 6-m water depth on an ocean beach is predicted well by a model that includes the effects of wave rollers and the bottom stress owing to the mean flow. Over the 90-day observational period, the measured and modeled setup are correlated (squared correlation above 0.59), and agree within about 30%. Although rollers may affect setup significantly on beaches with large amplitude (several meters high) sandbars and may be important in predicting the details of the cross-shore profile of setup, for the data discussed here, rollers have only a small effect on the amount of setup. Conversely, bottom stress (calculated using eddy viscosity and undertow formulations based on the surface dissipation, and assuming that the eddy viscosity is uniform throughout the water column) significantly affects setup predictions. Neglecting bottom stress results in underprediction of the observed setup in all water depths, with maximum underprediction near the shoreline where the observed setup is largest.
    Description: Funding was provided by the Office of Naval Research, the National Science Foundation, and the Army Research Office.
    Keywords: Setup ; Rollers ; Bottom stress
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    Current subsidence rates due to compaction of Holocene sediments in southern Louisiana (2007)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Geophysical Research Letters 33 (2006): L11403, doi:10.1029/2006GL026300.
    Description: Relative contributions of geologic and anthropogenic processes to subsidence of southern Louisiana are vigorously debated. Of these, shallow sediment compaction is often considered dominant, although this has never been directly observed or effectively demonstrated. Quantitative understanding of subsidence is important for predicting relative sea level rise, storm surge flooding due to hurricanes, and for successful wetland restoration. Despite many shallow borings, few appropriate stratigraphic and geotechnical data are available for site-specific calculations. We overcome this by determining present compaction rates from Monte Carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the Holocene of southern Louisiana. This approach generates distributions of present compaction rates that are not expected to exceed 5 mm/yr, but may locally. Locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes.
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    Hydrothermal sediments as a potential record of seawater Nd isotope compositions : the Rainbow vent site (36°14′N, Mid-Atlantic Ridge) (2006)
    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 Paleoceanography 21 (2006): PA3012, doi:10.1029/2006PA001273.
    Description: Geochemical compositions and Sr and Nd isotopes were measured in two cores collected ~2 and 5 km from the Rainbow hydrothermal vent site on the Mid-Atlantic Ridge. Overall, the cores record enrichments in Fe and other metals from hydrothermal fallout, but sequential dissolution of the sediments allows discrimination between a leach phase (easily leachable) and a residue phase (refractory). The oxy-anion and transition metal distribution combined with rare earth element (REE) patterns suggest that 1) the leach fraction is a mixture of biogenic carbonate and hydrothermal Fe-Mn oxy-hydroxide with no significant contribution from detrital material, and 2) 〉99.5% of the REE content of the leach fraction is of seawater origin. In addition, the leach fraction has an average 87Sr/86Sr ratio indistinguishable from modern seawater at 0.70916. Although we lack the εNd value of present day deep water at the Rainbow vent site, we believe that the REE budget of the leach fraction is predominantly of seawater origin. We suggest, therefore, that the leach fraction provides a record of local seawater εNd values. Nd isotope data from these cores span the period of 4-14 ka (14C ages) and yield εNd values for North East Atlantic Deep Water (NEADW) that are higher (-9.3 to -11.1) than those observed in the nearby Madeira Abyssal Plain from the same depth (-12.4 ± 0.9). This observation suggests that either the Iceland-Scotland Overflow Water (ISOW) and Lower Deep Water (LDW) contributions to the formation of NEADW are higher along the Mid-Atlantic Ridge than in the surrounding basins, or that the relative proportion of ISOW was higher during this period than is observed today. This study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water εNd values, and hence deep-water circulation patterns in the oceans, than is possible from other types of sediments.
    Description: VC is funded by the 2000 National Oceanography Centre, Southampton fellowship. Hydrothermal research at NOCS is funded through NERC core strategic science.
    Keywords: Nd isotope ; Hydrothermal ; Seawater
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    Evidence for asymmetric nonvolcanic rifting and slow incipient oceanic accretion from seismic reflection data on the Newfoundland margin (2006)
    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 Journal of Geophysical Research 111 (2006): B09402, doi:10.1029/2005JB003981.
    Description: Prestack depth migrations of seismic reflection data collected around the Ocean Drilling Program (ODP) Leg 210 transect on the Newfoundland nonvolcanic margin delineate three domains: (1) extended continental crust, (2) transitional basement, and (3) apparent slow spreading oceanic basement beyond anomaly M3 and indicate first-order differences between this margin and its well-studied conjugate, the Iberia margin. Extended continental crust thins abruptly with few observed faults, in stark contrast with the system of seaward dipping normal faults and detachments imaged within continental crust off Iberia. Transition zone basement typically appears featureless in seismic reflection profiles, but where its character can be discerned, it does not resemble most images of exhumed peridotite off Iberia. Seismic observations allow three explanations for transitional basement: (1) slow spreading oceanic basement produced by unstable early seafloor spreading, (2) exhumed, serpentinized mantle with different properties from that off Iberia, and (3) thinned continental crust, likely emplaced by one or more detachment or rolling-hinge faults. Although we cannot definitively discriminate between these possibilities, seismic reflection profiles together with coincident wide-angle seismic refraction data tentatively suggest that the majority of transitional basement is thinned continental crust emplaced during the late stages of rifting. Finally, seismic profiles image abundant faults and significant basement topography in apparent oceanic basement. These observations, together with magnetic anomaly interpretations and the recovery of mantle peridotites at ODP Site 1277, appear to be best explained by the interplay of extension and magmatism during the transition from nonvolcanic rifting to a slow spreading oceanic accretion system.
    Description: The SCREECH program was funded by U.S. National Science Foundation grant OCE-9819053 to Woods Hole Oceanographic Institution, by the Danish Research Foundation (Danmarks Grundforskningsfond), and by the Natural Science and Engineering Council of Canada. D. Shillington was also supported by NSF grant OCE-0241940 and by the University of Wyoming Graduate School. B. Tucholke acknowledges additional support from NSF grant OCE-0326714 and the Henry Bryant Bigelow Chair in Oceanography at Woods Hole Oceanographic Institution.
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    The St. Lawrence polynya and the Bering shelf circulation : new observations and a model comparison (2006)
    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 Journal of Geophysical Research 111 (2006): C09023, doi:10.1029/2005JC003268.
    Description: Using 14 year-long instrumented moorings deployed south of St. Lawrence Island, along with oceanographic drifters, we investigate the circulation over the central Bering shelf and the role of polynyas in forming and disseminating saline waters over the shelf. We focus also on evaluating the Gawarkiewicz and Chapman [1995] model of eddy production within coastal polynyas. Principal results include: 1) The northern central shelf near-surface waters exhibit westward flow carrying low-salinity waters from the Alaskan coast in fall and early winter, with consequences for water mass formation and biological production. 2) Within the St. Lawrence polynya, the freshening effect of winter advection is about half as large as the salting effect of surface brine flux resulting from freezing. 3) Brine production over the Bering shelf occurs primarily offshore, rather than within coastal polynyas, even though ice production per unit area is much larger within the polynyas. 4) We find little evidence for the geostrophic flow adjustment predicted by recent polynya models. 5) In contrast to the theoretical prediction that dense water from the polynya is carried offshore by eddies, we find negligible cross-shelf eddy density fluxes within and surrounding the polynya and very low levels of eddy energy that decreased from fall to winter, even though dense water accumulated within the polynya and large cross-shore density gradients developed. 6) It is possible that dense polynya water was advected downstream of our array before appreciable eddy fluxes materialized.
    Description: This work was supported by National Science Foundation grant OCE9730697 to the University of Alaska and grant OCE9730823 to the University of Washington. S. M. acknowledges the support of the National Science Foundation under OCE9811097 and of NASA under grant NNG04GM69G. The University of Hamburg contributions were funded by the Bundesminister für Bildung und Wissenschaft. Funding for the drifter deployment was made possible by the North Pacific Research Board, grant NPMRI T2130. Manuscript preparation was additionally supported by Office of Naval Research grants N00014-99-1-0345 and N00014-02-1-0305 to the University of Washington.
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    Linkages among runoff, dissolved organic carbon, and the stable oxygen isotope composition of seawater and other water mass indicators in the Arctic Ocean (2006)
    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 Journal of Geophysical Research 110 (2005): G02013, doi:10.1029/2005JG000031.
    Description: Concentrations of dissolved organic carbon (DOC) and δ18O values have been determined following sampling of runoff from a number of major arctic rivers, including the Ob, Yenisey, Lena, Kolyma, Mackenzie and Yukon in 2003-2004. These data are considered in conjunction with marine data for DOC, δ18O values, nutrients, salinity, and fluorometric indicators of DOC that were obtained as part of the Shelf-Basin Interactions program at the continental shelf-basin boundary of the Chukchi and Beaufort Seas. These marine data indicate that the freshwater component is most likely derived from regional sources, such as the Mackenzie, the Bering Strait inflow and possibly eastern Siberian rivers, including the Kolyma, or the Lena but not rivers further west in the Eurasian arctic. Contributions of freshwater from melted sea ice to marine surface waters appeared to be insignificant over annual cycles compared to runoff, although on a seasonal basis, freshwater from melted sea ice was locally dominant following a major sea-ice retreat into the Canada Basin in 2002. DOC concentrations were correlated with the runoff fraction, with an apparent meteoric water DOC concentration of 174 ± 1 μM (standard error). This concentration is lower than the flow-weighted concentrations measured at river mouths of the five largest Arctic rivers (358 to 917 μM), indicating that removal of terrigenous DOC during transport through estuaries, shelves and in the deep basin. DOC data indicate that flow-weighted concentrations in the two largest North American arctic rivers, the Yukon (625μM) and the Mackenzie (382 μM), are lower than in the three largest Eurasian arctic rivers, the Ob (825 μM), the Yenesey (858 μM) and the Lena (917 μM). A fluorometric indicator of chromophoric dissolved organic matter (CDOM) that has provided estimates of terrigenous DOC concentrations in the Eurasian Arctic was not correlated with DOC concentrations in the Amerasian marine waters studied, except below the upper Arctic Ocean halocline. Nutrient distributions and concentrations as well as derived nutrient ratios suggest the CDOM fluorometer may be responding to the release of chromophoric materials from continental shelf sediments. Shipboard incubation experiments with undisturbed sediment cores indicate that continental shelf sediments on the Bering and Chukchi Sea shelves are likely to be a net source of DOC to the Arctic Ocean.
    Description: The PARTNERS and SBI projects have been supported by the Office of Polar Programs of the U.S. National Science Foundation.
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    Meridional overturning circulation in the South Atlantic at the last glacial maximum (2006)
    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 Geochemistry Geophysics Geosystems 7 (2006): Q10N03, doi:10.1029/2005GC001226.
    Description: The geostrophic shear associated with the meridional overturning circulation is reflected in the difference in density between the eastern and western margins of the ocean basin. Here we examine how the density difference across 30°S in the upper 2 km of the Atlantic Ocean (and thus the magnitude of the shear associated with the overturning circulation) has changed between the last glacial maximum and the present. We use oxygen isotope measurements on benthic foraminifera to reconstruct density. Today, the density in upper and intermediate waters along the eastern margin in the South Atlantic is greater than along the western margin, reflecting the vertical shear associated with the northward flow of surface and intermediate waters and the southward flowing North Atlantic Deep Waters below. The greater density along the eastern margin is reflected in the higher δ 18O values for surface sediment benthic foraminifera than those found on the western margin for the upper 2 km. For the last glacial maximum the available data indicate that the eastern margin foraminifera had similar δ 18O to those on the western margin between 1 and 2 km and that the gradient was reversed relative to today with the higher δ 18O values in the western margin benthic foraminifera above 1 km. If this reversal in benthic foraminifera δ 18O gradient reflects a reversal in seawater density gradient, these data are not consistent with a vigorous but shallower overturning cell in which surface waters entering the Atlantic basin are balanced by the southward export of Glacial North Atlantic Intermediate Water.
    Description: This work was supported by NSF award OCE-9984989/OCE-0428803 to J.L.-S., NSF award OCE-9986748 to D.W.O. and W.B.C., NSF OCE-0222111 to C.D.C., and SEGRF fellowship at LLNL to J.M.
    Keywords: Last Glacial Maximum ; South Atlantic ; Meridional overturning circulation ; Oxygen isotopes ; Benthic foraminifera
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