Introduction

In recent years, with the increasing speed and capacity of distributed-memory parallel computers, considerable effort has been devoted to simulating ground motions induced by earthquakes in large basins [1]. Most of the work to date, however, is restricted to linear analyses. In fact, it is well known that the stress-strain behavior of soils is not linearly elastic for the entire range of loading of practical interest. The need for incorporating in the simulation a truly nonlinear soil model becomes particularly apparent when the soil system in a large basin with relatively soft sediments is excited by strong earthquake motions.

The simulation of earthquake response in a large basin must be accomplished by a numerical method. One of the techniques that is well suited for simulating wave propagation through heterogeneous media in large basins is the finite element method [1]. This method is often favored over other numerical techniques (such as the finite difference method and the boundary element method) since it can conveniently model material inhomogeneity, nonlinearity, and arbitrary geometries and loading. Also, the finite element method can tailor the mesh size to the local wavelength of propagating waves and make large-scale simulation feasible.

With better understanding of the physical principles in soil plasticity models and recent advances in parallel supercomputing, it is now possible to develop a nonlinear finite element system for three-dimensional dynamic elasto-plastic analysis that can be used to simulate nonlinear earthquake response in large basins on parallel computers. This is the main objective of the proposed research. This research will focus on the following aspects for developing such a system:

• Study various soil plasticity models and design numerical techniques to incorporate an appropriate plasticity model into a finite element wave propagation code.
• Design an efficient, accurate and economical numerical model for solving elasto-plastic problems with a large number of degrees of freedom.
• Implement the soil plasticity model and elasto-plasticity solver within a parallel finite element wave propagation code.
• Illustrate the new methodology by examining in detail the seismic response of an idealized basin.

It is expected that the proposed simulation of nonlinear earthquake response in elasto-plastic soils by this system will be among the pioneering efforts towards gaining a better understanding of the effect of nonlinear soil behavior on earthquake response in three-dimensional basins.