Strong Motion and Seismic Risk of Large Urban Regions

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In order to develop precisely the methods of strong ground motion prediction and seismic microzonation in large urban regions, the joint researches between Japan and China were carried out by using the records of strong seismic ground motions and long-period microseisms in the Tangshan and Shanghai regions. To examine these methods, we used the data of seismic damage. To predict seismic activity from the Japan islands to the Heubei region, we investigated the mechanism of generation and transfer of tectonic stress by numerical experiments.Strong ground motions at 5 temporary observation stations in near-field of the Tangshan Earthquake were estimated by the method using acceleration records of after shocks with magnitude of about 5 as an empirical Green function. Resulted seismic ground motions were corresponding with damage data. For example, the estimated accelerograms has less peak values than those of proposed by Chinese Intensity Table at the station of Cement Plant, which is located at rock site and had slight damage, even though the plant is in the inside of epicentral region with intensity XI. It shows that this method can simulate strong ground motions of high frequency reasonably.We estimated seismic risk in the Shanghai region on the basis of seismic activity in and around Shanghai and vibratile characteristics of ground obtained from the observation of long-period microseisms. We also estimated seismic response for space frame structures and seismic risk of urban lifelines in the central Shanghai.From large numerical experiments, it was shown that volcanic and seismic activities in the Japan islands were connected with those in the China continent by the transfer of tectonic stress.