Simulation of the seismic response of the Santiago basin, Chile

Abstract

Two mega-thrust earthquakes have struck the Santiago city, the economic and political center of Chile with more than 5.5 million inhabitants, causing extensive damage and high seismic intensities. In this study, we use the results of an ambient seismic noise tomography, gravimetric studies, deep wells, and local geophysical methods to develop three representative cross-sections along the Santiago Basin. Then we perform 2D dynamic numerical simulations using the finite-difference code 2DFD_DVS. The input ground motions are impulse signals polarized in the longitudinal, transverse, and vertical directions with respect to the profiles imposed inside the model domain. In addition, the one-dimensional (1D) response of the model was calculated to compare with the two-dimensional (2D) response. The constitutive model of the materials is a generalized Maxwell body with a constant quality factor. The velocity time-histories obtained in the model surface highlight significant amplification of the softer sediments in the basin and longer strong ground motion due to surface waves generated at the boundaries of rock outcrops. Aggravation factors of the 2D model with respect to the 1D response are calculated and indicate that the 1D approach resembles the 2D response in sites with stiff soils, but it cannot capture the basin edge effects in sites with soft sediments. Records of the six seismic stations closest to CD and EW cross-sections for the 2015 Mw 8.4 Illapel megathrust earthquake are consistent with numerical simulations in the frequency domain.