Three-dimensional nonlinear seismic ground motion modeling in basins

In this paper, we report on the development and application of a parallel numerical methodology for simulating large-scale earthquake-induced ground motion in highly heterogeneous basins whose soil constituents can deform nonlinearly. We target sedimentary basins with large contrasts in wavelengths for which regular grid methods become inefficient, and overcome the problem of multiple physical scales by using unstructured finite element triangulations. We illustrate the methodology with an example of an idealized basin, which contains a deep and a shallow sub-basin. The simulations show significant amplitude reduction of the ground accelerations due to inelastic soil behavior at sites above the deepest portions of the sub-basins, yet little shift in frequency. Under the assumption of linear anelastic material behavior, there is a rapid spatial distribution of the ground acceleration of the basin, which differs markedly from that for a one-dimensional (ID) analysis. This characteristic three-dimensional nature of the ground motion is preserved for the elastoplastic model. Concerning the ground displacement, the main qualitative difference between the elastic and inelastic models is the occurrence of significant permanent deformations in the inelastic case. These residual displacements can have practical implications for the design of long structures such as bridges and structures with large plan dimensions. (C) 2003 Elsevier Science B.V. All rights reserved.