Modeling 3D surface topography by finite‐difference method: Kobe‐JMA Station Site, Japan, Case Study

We propose a simple approach for treating non‐planar free‐surface boundary conditions that can be easily implemented into an existing finite‐difference code. The approach is based on the three‐dimensional staggered‐grid finite‐difference method (FDM, hereafter). The proposed scheme gives very good results when compared with other numerical methods. Its accuracy depends on how well the topography is matched by the 3D‐FD grid. Based on the proposed technique, we made a qualitative evaluation of the local topography effect on ground motion at KOB‐JMA site, Kobe, Japan. The local topography at JMA station amplifies the horizontal ground motion in the frequency range 1–3 Hz by a factor of less than two, and deamplifies it at frequencies around 5 Hz by a factor of five.