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

为了建立一个高精度的长周期运动估计数据库，我们进行了地下结构的探索、地震观测、地震运动分析以及二维或三维模型的理论模拟。研究结果如下：1)进行了微动阵列测量和移动微动测量。目标区域为关东盆地、德池盆地、尾谷地区、四国岛盆地、顺奈盆地、秋田盆地、鸟取盆地。其中一些地区附近发生了一些灾难性的地震。2)在关东盆地安装了地震仪，研究以长周期运动为主的面波是如何产生和放大的。成功地观察到，地震运动在盆地内部的持续时间越来越长，后期地震似乎是从盆地边缘扩散出来的。除观测外，还对研究期间发生的灾害性地震进行了余震观测，并对造成破坏的地表地质效应进行了实验评价。3)利用关东盆地东部的二维模型，阐明了盆地边缘产生和放大面波的机制。在此基础上，利用关东盆地三维模型进行了地面运动模拟，较完整地再现了地震波场。将该模拟应用于小地震，验证了模型的有效性，并能再现观测到的运动特征。为了在波形上达到精确的一致，有必要对该3D模型进行修改。

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.