1,721,025 research outputs found
Seismic tremor in subduction zones: Rock physics evidence
No full textEpisodic tremor and slip (ETS) have been correlated with rupture phenomena in subducting oceanic lithosphere at 30-45 km depth, where high V(P)/V(S) ratios, which suggest high-fluid pressures, have been observed. ETS, by accommodating slip in the down-dip portion of the subduction zone, may trigger megathrust earthquakes up-dip in the locked section. During dehydration experiments on serpentinite (typical rock of the oceanic lithosphere) at temperatures found in nature at 30-45 km depth (400-550 degrees C), we observe seismic signals in the form of acoustic emissions that closely resemble low frequency earthquakes, seismic tremor and regular earthquakes. Our findings support the concept that water released during dehydration reactions increases the pore pressures and can trigger ETS and regular earthquakes by reducing slip resistance. Citation: Burlini, L., G. Di Toro, and P. Meredith (2009), Seismic tremor in subduction zones: Rock physics evidence, Geophys. Res. Lett., 36, L08305, doi: 10.1029/2009GL037735
Experimental study of the seismic properties of the Eastern Alps (Italy) along the Aurina-Tures-Badia Valleys transet.
No full textIn order to better constrain the interpretation and the nature of the seismic reflectors, experimental measurements at high confining pressure (up to 300 MPa) and room temperature of the compressional wave velocity (Vp) on 10 samples representative of the most common lithologies along the Aurina (Ahrntal), Tures (Tauferer Tal), and Badia (Abtei Tal) Valleys profile (Eastern Alps, Italy) have been performed. For each sample, the speed of ultrasonic waves was measured in three mutually perpendicular directions, parallel and normal to the rock foliation and lineation. The main results are: (a) Good agreement between the calculated vs. measured modal compositions of the considered rocks, indicating that they were presumably equilibrated at the estimated P-T conditions; therefore, the seismic properties are representative of the crustal level indicated by the thermobarometry. (b) Measured and calculated average Vp are in good agreement, and are typical of mid-crustal level (6.0-6.5 km/s). Only the amphibolites show Vp typical of the lower crust (7.2 km/s). (c) The seismic anisotropy of metapelites is very high (12-27%), both with orthorhombic and transverse isotropy symmetry; amphibolites are transversely isotropic with an anisotropy of 8%; orthogneisses and granitoids are isotropic or weakly anisotropic. (d) The contacts between amphibolites and all other rock types may generate good reflections, provided they are not steeply inclined. Although the metamorphic foliation remains steeply inclined, discordant buried sub-horizontal igneous contacts may be detected
Rheological properties of magma from the 1538 eruption of Monte Nuovo (Phlegrean Fields, Italy): An experimental study
No full textThe rheology of natural, partially crystallized samples from Monte Nuovo (1538 AD) eruption have been
investigated using a high temperature, high pressure internally heated pressure vessel. Within the
temperature interval of investigation the samples exhibited Newtonian rheology at deformation strain rates
up to 10−4 s−1. At higher strain rates a decrease of viscosity with increasing strain rate (shear thinning),
eventually terminating in a sudden viscosity drop (stress weakening), was observed. Stress weakening occurred at higher applied strain rates and stresses with increasing temperature. The microstructural
analyses of the samples revealed that stress weakening resulted from strain localization, which occurred in brittle and viscous regimes at the lowest and highest temperatures investigated respectively. The different rheological behaviors of the investigated material is likely responsible for the changes in the dynamics of
magma ascent within the volcanic conduit during the eruption of Monte Nuovo volcano. We infer that the
occurrence of syn-eruptive decompression driven crystallization, observed in previous studies, induced
strong variations in the rheological properties of magma, which in turn was responsible for the changes of
eruptive style observed during the Monte Nuovo eruption
Seismic tremors: the rock physics interpretation
No full textsee Abstract VolumeIstituto Nazionale di Geofisica e Vulcanologia, Italy (INGV)
Centre National de la Recherche Scientifique (CNRS)
ExxonMobil Upstream Research CompanyUnpublishedErice, Italyope
Seismic tremors: the rock physics interpretation
No full textsee Abstract VolumeIstituto Nazionale di Geofisica e Vulcanologia, Italy (INGV)
Centre National de la Recherche Scientifique (CNRS)
ExxonMobil Upstream Research CompanyUnpublishedErice, Italyope
Measurement of calcite crystallographic preferred orientations by magnetic anisotropy and comparison to diffraction methods
No full text
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