11:30 AM - 11:45 AM
[S01-4-05] Exhaustive analysis of surface wave propagation in a combined use of active and passive surveys for detailed site characterization
Determining the soil geophysical properties related to seismic amplification, at sites where ground motion is being recorded, is a key effort in engineering seismology. Besides explaining local seismic response, it improves the robustness of the estimation of seismic attenuation and of earthquake magnitude. For the purposes of site characterization, surface wave (SW) methods are nowadays regarded as an established technique.
We present site characterization surveys conducted at selected sites of the Swiss strong motion network SSMNet; active and passive SW data were jointly acquired. The novelty we introduce with respect to previous works is the technique we use to derive the parameters of SW propagation. We have developed and apply a maximum likelihood technique for the joint analysis of Love and Rayleigh waves. They are identified in the collected data and selected with a Bayesian information criterion; wave parameters are estimated modeling jointly all recorded components. As outcome, SW dispersion data, Rayleigh wave ellipticity and prograde/retrograde sense of particle motion are retrieved. Originally developed for passive data, we have also adapted this technique for active acquisitions, accounting for the propagation of circular wave fronts. This allows us, in the surveys we present, i) to merge information from active and passive measurements, covering shallow and large depths; ii) to use the same 2D array for active and passive acquisitions (simplifying survey logistics). Finally, limited to active data, we have included the modeling of Rayleigh wave intrinsic attenuation. This enables the reconstruction of the damping ratio profile of the subsoil, besides that of shear wave velocity. We show that the joint assessment of the characteristics of SW propagation (velocity, ellipticity, sense of particle motion, attenuation) improves the robustness of their estimation, and also the reliability and completeness of the obtained subsurface geophysical models.
We present site characterization surveys conducted at selected sites of the Swiss strong motion network SSMNet; active and passive SW data were jointly acquired. The novelty we introduce with respect to previous works is the technique we use to derive the parameters of SW propagation. We have developed and apply a maximum likelihood technique for the joint analysis of Love and Rayleigh waves. They are identified in the collected data and selected with a Bayesian information criterion; wave parameters are estimated modeling jointly all recorded components. As outcome, SW dispersion data, Rayleigh wave ellipticity and prograde/retrograde sense of particle motion are retrieved. Originally developed for passive data, we have also adapted this technique for active acquisitions, accounting for the propagation of circular wave fronts. This allows us, in the surveys we present, i) to merge information from active and passive measurements, covering shallow and large depths; ii) to use the same 2D array for active and passive acquisitions (simplifying survey logistics). Finally, limited to active data, we have included the modeling of Rayleigh wave intrinsic attenuation. This enables the reconstruction of the damping ratio profile of the subsoil, besides that of shear wave velocity. We show that the joint assessment of the characteristics of SW propagation (velocity, ellipticity, sense of particle motion, attenuation) improves the robustness of their estimation, and also the reliability and completeness of the obtained subsurface geophysical models.