Modeling of 3D Basin Structures for Seismic Wave Simulations Based on Available Information on the Target Area: Case Study of the Osaka Basin, Japan

Practical procedures for modeling basin structure are proposed. One is to construct a smooth 3D basin structure model under and around the target site for low-frequency strong motion simulation. The other is to make a 1D velocity structure model just under the target site for high frequencies. These procedures were applied to the Osaka basin, Japan, in which numerous exploration studies were conducted before and after the 1995 Hyogoken-Nanbu (Kobe) Earthquake. The published results of those explorations in addition to those from our several investigations were compiled to construct the model. A two-dimensional third-order B-spline function was used to establish a smooth structure model from available depth data. Microtremor array observations were used to model the velocities and densities of the sedimentary layer structures. A four-layer model well explains the dispersion characteristics of Rayleigh waves that make up the microtremors. By adding a detailed shallow velocity structure to the top of the deeper four-layer model, adequate site responses for a wide frequency range of ground motions can be obtained. This proposed procedure can be used to determine the basement geometry of other sedimentary basins.