Local Velocity Structure from the Amplification of Surface Waves

Abstract:

We apply a new technique to retrieve local amplification from the amplitude of seismic surface waves, in various areas on Earth covered by dense seismic arrays. By taking the ratio of amplitudes measured at two close-by locations, and by averaging over many recordings, we are able to isolate the receiver-side contribution from the effects of structures at the source and along the propagation path. The technique is applied to Rayleigh-wave data measured in the 35-375s period-range, allowing us to construct amplification maps sensitive down to ~250 km depth. We assess the eliability of the method by performing various tests based on synthetic data. Since surface-wave amplification depth kernels demonstrate a strong sensitivity to shear velocity and attenuation, we invert for these parameters. To that purpose, we invert the observed amplification dispersion curves to generate best-fitting radial profiles using a neighbourhood algorithm approach. We employ this set of techniques to several regions of geological interest, and interpret the results in terms of local mantle dynamics.