Variation of earthquake ground motionwith depth

The variation of ground motion with depth is investigated in this paper, which is essential in determining the seis- mic design ground motion for embedded structures and pipelines. Firstly the earthquake ground motion on surface and in subsoil recorded by Hosokura Mine array of Japan and six California Strong Motion Instrumentation Pro- gram geotechnical arrays of the United States from about fifty moderate and strong earthquakes are described. Then the arrays were classified into three different categories according to their site conditions. Finally the varia- tion law of ground and sub-ground motion with depth is established as a result of a nonlinear regression analysis of the above-mentioned data. Through comparing the features in different sites, it is concluded that, in general, the amplitude (acceleration, velocity and displacement) of ground motion are decreasing with depth and the attenua- tion rate is higher in the shallow strata than that in deeper ones.