1,721,109 research outputs found
Preliminary 3D velocity model of Ischia Island from the inversion of active seismic data
No full textThe rule of dynamic strain to near source aftershock distribution of the 2014, Mw 6.0, Napa (California) earthquake
No full textThe rule of dynamic strain to near source aftershock distribution of the 2014, Mw 6.0, Napa (California) earthquak
The structural setting of the Ischia Island Caldera (Italy): first evidence from seismic and gravity data
No full textIschia Island is one of the active volcanoes of the Neapolitan area (Italy). Hazard assessment of active, densely populated volcano is primarily based on knowledge of the volcano’s past behaviour and of its present state. As a contribution to the definition of the present structural setting of Ischia Island, we constructed a new model of the shallow crust using geophysical data: seismic wave travel times and Bouguer anomaly data. We analysed these data sets through seismic tomography and gravity data inversion. The main results inferable from the 3D seismic and gravity images are the definition of the caldera rim along the perimeter of the island, as hypothesized by many authors, and the presence of a high velocity and density area inside the caldera consistent with extension of the resurgent block that characterizes the recent deformation of the island
BISTROP: Bayesian inversion of spectral-level ratios and p-wave polarities for focal mechanism determination
No full textThe analysis of earthquake focal mechanisms provides information about the stress regime, fault geometry, and deformation processes acting in a given region. Generally, the techniques aimed at determining focal mechanism are designed to work in a specific magnitude range operating both in the time and frequency domain and using different data (e.g., P polarities, S-wave polarization, S/P-amplitude ratios, etc.). In this article, we present a new method, Bayesian inversion of spectral-level ratios and P-wave polarities (BISTROP), that can be applied to both small and moderate-to-large magnitude events. BISTROP uses a Bayesian approach to jointly invert the long-period spectral- level P/S ratios and the P polarities to infer the fault-plane solutions. We apply this method to analyze synthetic data as well as those generated by real earthquakes. We find that the obtained solutions for moderate earthquakes are comparable with those obtained using moment tensor inversion, and they are more constrained with respect to the solutions obtained using only P-polarity data for small earthquakes
Cyclic Behaviour of Steel Beam-to-Column Connection: Interpretation of Experimental Results.
No full textFluid-Triggered Aftershocks in an Anisotropic Hydraulic Conductivity Geological Complex: The Case of the 2016 Amatrice Sequence, Italy
Full text linkThe mechanism by which faults interact each other is still a debated matter. One of the main issues is the role of pore-pressure diffusion in the delayed triggering of successive events. The 2016 Amatrice–Visso–Norcia seismic sequence (Central Apennines, Italy) provides a suitable dataset to test different physical mechanisms leading to delayed events. The sequence started on August 24, 2016, with the Amatrice mainshock (MW = 6), and was followed after more than 60 days by events in Visso (MW = 5.4) and Norcia (MW = 5.9). We analyzed the contribution of the static stress change and the role of fluids in the delayed triggering. Through 3D poroelastic modeling, we show that the Amatrice mainshock induced a pore-pressure diffusion and a normal stress reduction in the hypocentral area of the two aftershocks, favoring the rupture. Our parametric study employs a simple two-layered conductivity model with anisotropy in the seismogenic layer, characterized by larger conductivity values (K > 10−5 m/s) along the NNW-SSE direction. The one-way coupled pore-pressure 3-D diffusion modeling predicts the maximum increase of the pore pressure at the location of the two Visso earthquakes 60 days after the mainshock. The occurrence of anisotropic diffusivity is supported by the pattern of active faults and the strong crustal anisotropy documented by S-wave splitting analysis. We conclude that the temporal evolution of the sequence was controlled by the anisotropic diffusion of pore-pressure perturbations through pre-existing NNW-trending fracture systems
Using ground motion prediction equations to monitor variations in quality factor due to induced seismicity: a feasibility study
No full textSub-surface operations for energy production such as gas storage, fluid reinjection or hydraulic fracking may modify the physical properties of the rocks, in particular the seismic velocity and the anelastic attenuation. The aim of the present study is to investigate, through a synthetic test, the possibility of using empirical ground-motion prediction equations (GMPEs) to observe the variations in the reservoir. In the synthetic test, we reproduce the expected seismic activity (in terms of rate, focal mechanisms, stress drop and the b value of the Gutenberg-Richter) and the variation of medium properties in terms of the quality factor Q induced by a fluid injection experiment. In practice, peak-ground velocity data of the simulated earthquakes during the field operations are used to update the coefficients of a reference GMPE in order to test whether the coefficients are able to capture the medium properties variation. The results of the test show that the coefficients of the GMPE vary during the simulated field operations revealing their sensitivity to the variation of the anelastic attenuation. The proposed approach is suggested as a promising tool that, if confirmed by real data analysis, could be used for monitoring and interpreting induced seismicity in addition to more conventional techniques
Cyclic Behaviour of Steel Beam-to-Column Connection: Interpretation of Experimental Results.
No full text1-D/2-D P-velocity models of Mt. Vesuvius volcano from the inversion of TomoVes96 first arrival time data
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