Effect of Random Inhomogeneity in the Propagation Path on Short Distance Seismic Ground Motion Records

Abstract

The inhomogeneity of the medium in the seismic propagation path is inferred to vary depending on regions and depth. To improve the accuracy of numerical simulations of earthquake motion in the random media adequate inhomogeneity parameters consistent with the region where the seismic waves propagate are needed. In this study inland earthquakes are focused on and strength(ε) and correlation length(a) of inhomogeneity distribution of seismic velocity in the propagation path are inferred. First ε²/a values of inhomogeneity of seismic velocity in the propagation path were inferred based on KiK-net observation records whose hypocentral distances are between 10km and 60km. In order to estimateε²/a least square regression analysis was performed in which fitting of the envelope time series of observed records and the calculated envelope based on scattering theories. It was revealed that the estimated values of ε²/a from the short-distance (about 20km) records were greater than values in the previous studies. Then numerical simulations were performed in order to study the influence of the inhomogeneity on seismic wave. Three different 3D random inhomogeneous models were set up and the finite difference method was applied to obtain velocity time histories in the random media. As a result dependency of ε²/a on the hypocentral distance similar to the observed records has been confirmed. In the analyzed distance range the simulation result based on the inhomogeneity parameters of ε=0.05 and a=4km has relatively agreed with the result from the observed records.