In the earthquake resistant design process, lateral forces that the structure must withstand without failure[15] are usually prescribed through seismic design spectra. The amplitude of the lateral force is determined to a large extent, by the ground motion that can be expected in the vicinity of the structure. Thus, knowledge of the ground motion becomes essential for reducing the earthquake risk to the general population in earthquake-prone regions.
Seismologists and engineers have made significant progress in simulating ground motion by a variety of simplified numerical and analytical methods such as one- and two-dimensional local models. These can help explain observed behavior in certain situations. Observations of ground motion during recent strong earthquakes have shown, however, that 3-D local site effects, which are normally given only passing attention in design, can be extremely important, and can adversely affect structural safety. Three common effects often observed in basins or sedimentary valleys are an amplification, and significantly longer duration of the surface ground motion with respect to that in rock, and a more rapid spatial variation of the ground motion, which can cause large differential base motion of extended structures such as bridges or dams.
Therefore, a complete quantitative understanding of strong ground motion in large basins requires a simultaneous consideration of the 3-D effects of the earthquake source, propagation path, and local site conditions. See [1] for a general overview, and [25, 46, 16, 19, 41, 33, 32], for instance, for representative recent work in this field including 3D simulations. The large scale associated with modeling strong ground motion in large basins places enormous demands on computational resources, and renders this problem one of great complexity.
In recent years, a series of numerical methods, such as finite-difference methods (FDM), boundary-element methods (BEM), finite element methods(FEM), and pseudo-spectral methods have been used to simulate earthquake ground motions. Results from such simulations have contributed to the understanding of earthquake response of basins, but the results so far are far from complete.
The objective of this research is to develop a numerical implementation to simulate the ground motion of large basins during strong earthquakes and then to study seismic site effects in realistic sedimentary basins.
Based on the review of the related numerical work and our initial investigation, we have found that finite element methods present advantages over other methods to fulfill this task. There remain, however, several challenges to complete a 3-D FEM model: