Soil amplification in the Santiago city, Chile, due to shallow crustal earthquakes

Three-dimensional physics-based numerical simulations (3D-PBS) of the seismic response of the Santiago Basin, Chile, were performed considering a large-scale velocity model and shallow crustal earthquake scenarios, associated with the west-verging thrust San Ramón Fault. Numerical results show that competent gravelly soils in the center of the basin respond with low seismic amplification and shorter durations of strong ground motions, unlike less competent fine-grained soils in the northern area. A significant increase in the seismic intensities is observed in the vicinity of rock outcrops, attributable to the generation of surface waves. Seismic amplification factors were calculated with respect to a reference site on gravel and their values show high levels of amplification in the vicinity of the seismic source, and on soils with low shear wave velocities (V_s) and long fundamental vibration periods. On the other hand, empirical ground motion models (GMM) were used to estimate amplification factors for peak ground accelerations and spectral accelerations at various periods. Results from GMMs and 3D-PBS were compared, showing similarities in the attenuation pattern on stiff soils, but differences in soils with low V_s. Moreover, 3D-PBS captured site effects associated with the local geomorphology, unlike GMMs.