Three-dimensional  Finite Difference Method and Hybrid Modeling of Earthquake Ground Motion

Abstract
A new two-step hybrid technique (hybrid) has been developed to estimate the earthquake ground motion in 3D local models excited by external sources.The main use of the technique the to fast evaluation of site effects and seismic hazard, because our technique needs less computer memory and time than all-in-one source-path-site computational methods.The first step of the hybrid requires an arbitrary 3D method (e.g.finite-difference (FD), discrete wavenumber, ray, or analytical solution) to compute 3-component excitation on a grid box surrounding a site of interest. A particular excitation contains information on the source and path effects and is saved on disk as a time history.Depending on the method used, the 1 st step may also contain non-planar topography.The second step (3D FD) employs local structure and topography inside the excitation box and a procedure that exactly couples the 1 st step results with the 2nd step. The speedup of the hybrid method is made possible through the computation of the excitation (saved on disc) in the 1st step, and the numerous uses of the FD on irregular grids in the 2 nd step of the hybrid. The 2nd step computational model can be just a small spatial fraction of the original source-path-site model. A practical parameter study example of a point double-couple source and regional topography model (applied in the 1 st step) with a local low-velocity basin structure and ridge (both applied in the 2 nd step only) is presented.