1,720,965 research outputs found
Determination of the seismic moment tensor for local events in the South Shetland Islands and Bransfield Strait.
No full textSix events with magnitude between 3 and 5.6 have been analysed based on regional waveforms recorded by the temporal Seismic Experiment in Patagonia and Antarctica seismic broad-band network in the Bransfield Strait and the South Shetland Islands in the period 1997–1998. The source parameters have been retrieved using a robust methodology (INDirect PARametrization) to stabilize the inversion of a limited number of noisy records. This methodology is particularly important in oceanic environments, where the presence of seismic noise and the small number of stations makes it difficult to analyse small magnitude events. The source mechanisms obtained are quite variable but consistent with the active tectonic processes and the complicated structure of the South Shetland Island region
INPAR, CMT and RCMT aseismic moment solutions compared for the strongest damaging events (M≥4.8) occurred in the Italian region in the last decade
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P-SV multimode summation differential seismograms for layered structures: extension to high frequencies and oceanic structural models
No full textCrust and Upper Mantle Structure in the Caribbean Region by Group Velocity Tomography and Regionalization
No full textAn overview of the crust and upper mantle structure of Central America and the Caribbean region is presented as a result of the processing of more than 200 seismograms recorded by digital broadband stations from SSSN and GSN seismic networks. Group velocity dispersion curves are obtained in the period range from 10s to 40s by FTAN analysis of the fundamental mode of the Rayleigh waves; the error of these measurements varies from 0.06 and 0.09 km/s.From the dispersion curve, seven tomographic maps at different periods and with average spatial resolution of 500 km are obtained. Using the logical combinatorial classification techniques, eight main groups of dispersion curves are determined from the tomographic maps and eleven main regions, each one characterized by one kind of dispersion curves, are identified. The average dispersion curves obtained for each region are extended to 150s by adding data from a larger-scale tomographic study (VDOVIN et al., 1999) and inverted using a nonlinear procedure. A set of models of the S-wave velocity vs. depth in the crust and upper mantle is found as a result of the inversion process.In six regions we identify a typically oceanic crust and upper mantle structure, while in the other two the models are consistent with the presence of a continental structure. Two regions, located over the major geological zones of the accretionary crust of the Caribbean region, are characterized by a peculiar crust and upper mantle structure, indicating the presence of lithospheric roots reaching, at least, about 200 km of depth
Surface wave tomography and seismic source studies at Campi Flegrei (Italy).
No full textWe analyse a set of events, recorded in March 1984 during a period of intense seismicity of the last bradyseismic crisis, to determine shallow velocity models and seismic source moment tensors in the Campi Flegrei region.
The velocity models of the crust are obtained by surface wave tomography. Two inland negative anomalies of group velocity resulting in our tomographic maps well agree with previous independent measurements whereas a third anomaly, located in the Pozzuoli Gulf and not evidenced by previous studies, is in correspondence with the caldera position. The inversion of the dispersion curves allows us to extend the already available velocity models within the uppermost 2 km of the crust.
The obtained models are employed to study seismic source features by the moment tensor analysis. Preliminary synthetic tests are performed in order to minimise artefacts in the moment tensor solutions possibly due to numerical noise, to station distribution or to the structural modelling approximation. Most of the investigated earthquakes are deviatoric mechanisms and the increase of the isotropic component is observed in connection with the change of the seismicity rate in the investigated temporal windo
3-D structure of the crust and uppermost mantle at the junction between the Southeastern Alps and External Dinarides from ambient noise tomography
Full text linkWe use ambient noise tomography to investigate the crust and the uppermost mantle structure beneath the junction between the Southern Alps, the Dinarides and the Po Plain. We obtained Rayleigh wave empirical Green's functions from cross-correlation of vertical component seismic recordings for three years (2010-2012) using stations from networks in Italy, Slovenia, Austria, Croatia, Serbia and Switzerland. We measure group and phase velocity dispersion curves from the reconstructed Rayleighwaves in the period range 5-30 and 8-37 s, respectively, andwe invert the surfacewave velocities for tomographic images on a grid of 0.1° ×0.1°. After the tomography, the group velocities are then inverted to compute the 3-D shear wave velocity model of the crust and the upper mantle beneath the region. Our shear wave velocity model provides the 3-D image of the structure in the region between Northeastern Italy, Slovenia and Austria. The velocity variations at shallow depths correlate with known geological and tectonic domains. We find low velocities below the Po Plain, the northern tip of the Adriatic and the Pannonian Basin, whereas higher velocities characterize the Alpine chain. The vertical cross-sections reveal a clear northward increase of the crustal thickness with a sharp northward dipping of the Moho that coincides at the surface with the leading edge of the Alpine thrust front adjacent to the Friuli Plain in Northeastern Italy. This geometry of the Moho mimics fairly well the shallow north dipping geometry of the decollement inferred from permanent GPS velocity field where high interseismic coupling is reported. From the northern Adriatic domain up to the Idrija right lateral strike-slip fault system beneath Western Slovenia, the crustal thickness is more uniform. Right across Idrija fault, to the northeast, and along its strike, we report a clear change of the physical properties of the crust up to the uppermost mantle as reflected by the lateral distribution of both group and phase velocity anomalies at relevant periods. Idrija fault is therefore interpreted as a subvertical fault sampling the whole crust. Our 3-D velocity model favours crustal thickening with Adria underthrusting the Alps at a shallow angle north of the Friuli Plain where much of the convergence is absorbed and where the destructive 1976 M s 6.5 thrust Friuli earthquake sequence took place. In Western Slovenia, the deformation is accommodated by strike-slip motion along the Idrija strike-slip fault system where the destructive 1511 M w 6.9 right lateral strike-slip event occurred
Source moment tensors of the earthquake swarm in Abu-Dabbab area, south east-Egypt
No full textSeismic sources of a big swarm occurred in August 2004 have been studied by investigation of the moment tensors of 15 earthquakes with magnitudes range from 1.7 to 3.7. For each selected event, two sets of moment tensor inversions were carried out. The first one with fixed epicentral coordinates and the second one with variable epicentral coordinates. The data fit between observed and synthetic seismograms was computed for an elastic layered media, and minimized using a least squares algorithm. The obtained fault plane solution for each event is in agreement with the few reliable first arrival polarities. The resulting source time functions, characterized by one or two peaks, indicate that event small events might be associated with complex sources. The resulting focal mechanisms of the selected events represent different styles of faulting (normal and reverse with strike slip faulting mechanisms). The normal faulting events are characterized by focal depths larger than 7 km and the reverse ones are shallower with focal depths less than 6 km. A non-double-couple component, compensated linear-vector dipole (CLVD) ratio up to 35% is obtained for some events. The presence of some events with high CLVD ratio, besides the initiation of a high-level seismic activity, in the Abu-Dabbab area, without a large seismic main shock, led us to suggest that the August 2004 swarm might be due to igneous activity, increasing of fluid pressure and gases being consistent with the relatively high heat flow of the area
Shear-wave velocity models and seismic sources in Campanian volcanic areas: Vesuvio and Campi Flegrei
No full textAntarctic Seismographic Argentinean-Italian Network and the progress in the study of structural properties and stress conditions in the Scotia Sea region
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