A study on construction of databases for high-precision prediction of long period motions on sedimentary basin

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In order to construct a database for high precise estimation of long period motions, we have performed explorations of subsurface structure, earthquake observation, analysis of earthquake motions, and theoretical simulation with 2D or 3D model. The results are as follows.1) Microtremor array measurements and mobile microtremor measurements were conducted. The target areas are Kanto basin, Tokachi basin, Ojiya area, the basins in Shikoku island, Shonai basin, Akita basin, Tottori basin. Some disastrous earthquakes occurred near some of them. In addition to the measurements, fundamental techniques have been developed, for example, high performance heuristic method and simultaneous inversion with another data set.2) Seismometers were installed on Kanto basin to investigate how the surface waves which mainly consist of long period motions were generated and amplified. It was successfully observed that the duration of the earthquake motions was getting long inside of the basin and the later phases looked to be spread from the edge of the basin. In addition to the observation, we conducted aftershock observations of the disastrous earthquakes that occurred in this research term, and the effects of surface geology, which cause the damage were experimentally evaluated.3) The mechanism to generate and amplify the surface waves from the basin edge was made clear using 2D model of the eastern part of Kanto basin. Furthermore, the ground motion simulation with 3D model of Kanto basin was performed to reproduce completely the seismic wave-field. This simulation was applied to the small earthquakes to confirm the validity of the model, and the characteristics of observed motions could be reproduced. To aim for the precise agreement in waveforms, it is necessary to modify this 3D model.