Propagation and Scattering of Seismic Waves in Complex media at Different Scales

Abstract

We analyzed the surface waves originated by active or passive seismic sources, looking at the scattering and propagation features at different scales: the Irpinia fault system (~100 km), the Solfatara (~100 m) and a masonry bridge (~10 m). We obtained an S-wave model of the Solfatara, through the joint inversion of the measured phase and group velocity dispersion curves. The final model highlights a medium more saturated in water in the SW domain with respect to the NE one; the geoelectric analysis outlines low resistivity values in the same place where we obtained a decrease of the S-wave velocity. Because of the high scattering properties of the Solfatara we characterize it by means of the mean free path (MFP) and the transport mean free path (TMFP). The former was measured through the ratio between the coherent and incoherent intensity. We described the medium as homogeneous with anomalies having the radius smaller than 5 m and a small contrast in terms of velocity and density with the surrounding medium. The latter was measured fitting the coda decay of the seismic signals and from the slope of the linear regression, we derived a characteristic length that accounts for the TMFP and anelastic attenuation. We detected and measured, in term of relative velocity variation, the progressive damage induced onto a masonry bridge by means of the coda wave interferometry. Finally, starting from the noise acquisition, we recovered the Green’s functions between the couples of stations, we measured the group velocity dispersion curves and inverted them in order to obtain an S-wave model for the area. This model points out a low value of S waves velocity in the region bordered by the faults of the Irpinia earthquake, which could be related with the presence of fluids.