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  • Agu
  • American Chemical Society (ACS)
  • Blackwell Publishing Ltd
  • Periodicals Archive Online (PAO)
  • 2005-2009  (2.289)
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  • 1
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    On the relevance of Born theory in global seismic tomography (2007)
    Agu
    Details
    Publikationsdatum: 2021-01-27
    Beschreibung: Does the application of seismic Born theory, as opposed to simpler ray theory, lead to an improvement in tomographic images of the Earth? In recent publications, Montelli et al. (2004a, 2004b) and van der Hilst and de Hoop (2005) among others have expressed opposite opinions. We propose a quantitative approach to the comparison of tomographic images, which we apply to the case of surface-wave phase velocity maps derived with Born vs. ray theory.
    Beschreibung: Published
    Beschreibung: L06302
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): global seismic tomography ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 2
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    Three-dimensional instantaneous mantle flow induced by subduction (2007)
    Agu
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    Publikationsdatum: 2021-01-27
    Beschreibung: We conduct three-dimensional subduction experiments by a finite element approach to study flow around slabs, which are prescribed based on a transient stage of upper mantle subduction from a laboratory model. Instantaneous velocity field solutions are examined, focusing on the toroidal vs. poloidal components as a function of boundary conditions, plate width, and viscosity contrast between slab and mantle. We show how the slab-to-mantle viscosity ratio determines the strength of toroidal flow, and find that the toroidal flow component peaks for slab/mantle viscosity ratios ~100 independent of slab width or geometry.
    Beschreibung: Published
    Beschreibung: L08304
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): mantle flow ; subduction ; 04. Solid Earth::04.01. Earth Interior::04.01.03. Mantle and Core dynamics
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 3
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    Sources, size distribution and downwind grounding of aerosols from Mt. Etna (2007)
    Agu
    Details
    Publikationsdatum: 2021-02-17
    Beschreibung: The number concentrations and size distributions of aerosol particles 〉0.3 mm diameter were measured at the summit of Mount Etna and up to 10 km downwind from the degassing vents during July and August 2004. Aerosol number concentrations reached in excess of 9 106 L 1 at summit vents, compared to 4–8 104 L 1 in background air. Number concentrations of intermediate size particles were higher in emissions from the Northeast crater compared to other summit crater vents, and chemical composition measurements showed that Northeast crater aerosols contained a higher mineral cation content compared to those from Voragine or Bocca Nuova, attributed to Strombolian or gas puffing activity within the vent. Downwind from the summit the airborne plume was located using zenith sky ultraviolet spectroscopy. Simultaneous measurements indicated a coincidence of elevated ground level aerosol concentrations with overhead SO2, demonstrating rapid downward mixing of the plume onto the lower flanks of the volcano under certain meteorological conditions. At downwind sites the ground level particle number concentrations were elevated in all size fractions, notably in the 2.0–7.5 mm size range. These findings are relevant for assessing human health hazard and suggest that aerosol size distribution measurements may aid volcanic risk management.
    Beschreibung: Published
    Beschreibung: D10302
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): aerosols ; Mount Etna ; 01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 4
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    Astronomic calibration of the late Eocene/early Oligocene Massignano section (central Italy) (2007)
    Agu
    Details
    Publikationsdatum: 2021-01-25
    Beschreibung: We present an astronomically tuned polarity timescale for the late Eocene/early Oligocene based on a cyclic limestone/marls sedimentary succession exposed at Massignano, Italy (GSSP for the Eocene- Oligocene boundary). Here we applied spectral analysis techniques to the high-resolution magnetic susceptibility record. The results provide clear evidence of a regular and cyclic signal that allows us to discard a stochastic mechanism as controlling these fluctuations. Conversely, these outcomes reveal the presence of stable and notable periodicities that are in tune with those associated with orbital forcing. Through a cyclostratigraphic analysis of the rhythmic sedimentary alternations and combination with the results of time series analysis of the proxy record, we refine the late Eocene portion of the GPTS. Through astronomical tuning of the rhythmic sedimentary alternations to recent astronomically calculated variations of Earth’s orbit we recalibrated the polarity boundaries ages and the main stratigraphic events recognized throughout the sedimentary record. Among these, an age of 33.714 Ma is proposed for the E/O boundary.
    Beschreibung: Published
    Beschreibung: Q07012
    Beschreibung: reserved
    Schlagwort(e): environmental magnetism; ; Eocene/Oligocene ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 5
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    Assessment of temperature, trace species, and ozone in chemistry-climate model simulations of the recent past (2007)
    Agu
    Details
    Publikationsdatum: 2021-06-08
    Beschreibung: Simulations of the stratosphere from thirteen coupled chemistry-climate models (CCMs) are evaluated to provide guidance for the interpretation of ozone predictions made by the same CCMs. The focus of the evaluation is on how well the fields and processes that are important for determining the ozone distribution are represented in the simulations of the recent past. The core period of the evaluation is from 1980 to 1999 but long-term trends are compared for an extended period (1960–2004). Comparisons of polar high-latitude temperatures show that most CCMs have only small biases in the Northern Hemisphere in winter and spring, but still have cold biases in the Southern Hemisphere spring below 10 hPa. Most CCMs display the correct stratospheric response of polar temperatures to wave forcing in the Northern, but not in the Southern Hemisphere. Global long-term stratospheric temperature trends are in reasonable agreement with satellite and radiosonde observations. Comparisons of simulations of methane, mean age of air, and propagation of the annual cycle in water vapor show a wide spread in the results, indicating differences in transport. However, for around half the models there is reasonable agreement with observations. In these models the mean age of air and the water vapor tape recorder signal are generally better than reported in previous model intercomparisons. Comparisons of the water vapor and inorganic chlorine (Cly) fields also show a large intermodel spread. Differences in tropical water vapor mixing ratios in the lower stratosphere are primarily related to biases in the simulated tropical tropopause temperatures and not transport. The spread in Cly, which is largest in the polar lower stratosphere, appears to be primarily related to transport differences. In general the amplitude and phase of the annual cycle in total ozone is well simulated apart from the southern high latitudes. Most CCMs show reasonable agreement with observed total
    Beschreibung: Published
    Beschreibung: D22308
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): Assessment of temperature ; 01. Atmosphere::01.01. Atmosphere::01.01.01. Composition and Structure
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 6
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    Influence of carbon dioxide on the large-scale dynamics of magmatic eruptions at Phlegrean Fields (Italy) (2007)
    Agu
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: Carbon dioxide is the second most abundant volatile species in magmas after water (Johnson et al., 1994) but its role on eruption dynamics is still largely unknown. The effects of the presence of CO2 in the Agnano Monte Spina eruption (4100 BP, Phlegrean Fields, Italy) are here evaluated by simulating the eruption dynamics from the base of the volcanic conduit up into the atmosphere. The numerical simulations consider multiphase flow dynamics and couple the steady-state, one-dimensional magma ascent model of Papale (2001) and the transient, axisymmetric pyroclast dispersal model of Neri et al. (2003). The main input parameters of the models were based on eruptive conditions estimated from the deposits. A parametric study has been performed on H2O and CO2 concentrations in the erupted magma. The addition of CO2 results in increased volatile saturation pressure and complex non-linear changes in the conduit flow. Nonetheless, within the range of conditions explored, this volatile scarcely affects the eruption style and dynamics in the atmosphere, which are principally controlled by the H2O content. The different roles of the two volatiles in the large-scale eruption dynamics are mostly the result of the competing changes induced by CO2 on vent conditions.
    Beschreibung: Published
    Beschreibung: L06318
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): carbon dioxide ; Phlegrean Fields ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 7
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    Physical and transport properties of isotropic and anisotropic cracked rocks under hydrostatic pressure (2007)
    Agu
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: A key consequence of the presence of microcracks within rock is their significant influence upon elastic anisotropy and transport properties. Here two rock types (a basalt and a granite) with contrasting microstructures, dominated by microcracks, have been investigated using an advanced experimental arrangement capable of measuring porosity, P wave velocity, S wave velocity, and permeability contemporaneously at effective pressures up to 100 MPa. Using the Kachanov (1994) noninteractive effective medium theory, the measured elastic wave velocities are inverted using a least squares fit, permitting the recovery of the evolution of crack density and aspect ratio with increasing isostatic pressure. Overall, the agreement between measured and predicted velocities is good, with average error less than 0.05 km/s. At larger scales and above the percolation threshold, macroscopic fluid flow also depends on the crack density and aspect ratio. Using the permeability model of Gue´guen and Dienes (1989) and the crack density and aspect ratio recovered from the elastic wave velocity inversion, we successfully predict the evolution of permeability with pressure for direct comparison with the laboratory measurements. We also calculate the evolution of the crack porosity with increasing isostatic pressure, on the basis of the calculated crack density, and compare this directly with the experimentally measured porosity. These combined experimental and modeling results illustrate the importance of understanding the details of how rock microstructures change in response to an external stimulus when predicting the simultaneous evolution of rock physical properties.
    Beschreibung: Published
    Beschreibung: B04202
    Beschreibung: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Beschreibung: JCR Journal
    Beschreibung: open
    Schlagwort(e): microcracked ; rocks ; 04. Solid Earth::04.01. Earth Interior::04.01.04. Mineral physics and properties of rocks
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 8
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    Impact of the Minoan tsunami of Santorini. Simulated scenarios in the Eastern Mediterranean (2007)
    Agu
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: We have simulated the impact of the tsunami generated by the Late Bronze Age (LBA) volcanic eruption of Santorini on the Eastern Mediterranean. Two different tsunami triggering mechanisms were considered: a caldera collapse and pyroclastic flows/surges entering the sea. Simulations include the ‘‘worst’’ input conditions in order to evaluate the maximum possible impacts, but also ‘‘lighter’’ input conditions, compatible with the lack of any tsunami trace on the Northern coasts of Crete. In all the simulations, tsunami propagation is mainly confined to the Southern Aegean. Outside the Aegean, the tsunami impact was negligible and not responsible for the slide-slumping of fine-grained pelagic and/or hemipelagic sediments considered the sources of the sporadically located seadeposits in the Ionian Sea and of the widespread megaturbidite deposits localized in the Ionian and Sirte Abyssal Plains.
    Beschreibung: Published
    Beschreibung: L18607
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): Minoan tsunami ; Santorini ; eastern Mediterranean ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 9
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    Azimuth-dependent amplification of weak and strong ground motions within a fault zone (Nocera Umbra, central Italy) (2007)
    Agu
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: During three moderate-magnitude earthquakes occurred in September–October 1997 in the central Apennines, Italy, accelerations larger than 0.5 g were recorded in the town of Nocera Umbra, 10 to 15 km N-NW of the epicenters. The accelerograph is sited in a fault zone, close to a N30 E tectonic contact. Six temporary seismological stations installed across the fault recorded 82 aftershocks occurred in two seismogenic zones: the Colfiorito-Sellano area, S-SE of the array, and the Gualdo Tadino area, to the north. The array data reveal large variations in terms of both peak ground motions and spectral amplitudes. Within the fault zone, amplifications show a strong dependence on the source azimuth. At the accelerograph site, the effects are particularly large for events from S-SE: peak ground motions are a factor of 14 larger than those of a reference site and conventional spectral ratios attain amplitudes as large as 50 at 7 Hz along the N30 E direction of motion, parallel to the strike of the fault. Nineteen strong motion accelerograms were then used to compare ground motion properties between weak and strong events up to M0 = 1.2 1025 dyn cm. A particle motion analysis shows that the directional effect is also present in the strongest motions, even though the amplification of peak ground motion decreases when M0 increases. Results from stochastic simulations indicate that such a behavior is not due to nonlinearity: applying the empirical weak motion transfer functions in a purely linear model the observed peak ground motions of the largest events are fit satisfactorily.
    Beschreibung: Published
    Beschreibung: 2156
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): site effects ; fault zone ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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  • 10
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    Reply to comment by Giuliano F. Panza on “Rarely observed short-period (5–10 s) suboceanic Rayleigh waves propagating across the Tyrrhenian Sea” (2007)
    Agu
    In:  Panza, G. F. (2006), Comment on ‘‘Rarely observed short-period (5– 10 s) suboceanic Rayleigh waves propagating across the Tyrrhenian Sea’’ by A. Rovelli et al., Geophys. Res. Lett., 33, L10309, doi:10.1029/2005GL025584.
    Details
    Publikationsdatum: 2017-04-04
    Beschreibung: We thank Giuliano F. Panza for the interest demonstrated in our study and for having pointed out the error in Figure 3 of Rovelli et al. [2004, hereinafter referred to as R2004GRL]. In his comment, Panza writes that a similar phenomenon was already reported by him in an old paper. This statement is not correct and we feel that probably we did not emphasized enough the innovative character of R2004GRL. His comment gives us the opportunity of better explaining that the phenomenon we observe in the Tyrrhenian Sea is different from those studied by Panza and coauthors.
    Beschreibung: Published
    Beschreibung: L10310
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): Reply ; 04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
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