Earthquake Disaster Evaluation Based on Estimation of Deep Underground Structure and Observation of Strong Ground Motion in Deep Sedimentary Basins

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Our target area is Sapporo urban region with almost 2 millions population, that is located on a deep sedimentary basin. We have conducted research there on the following five heads: 1) geological environment, 2) seismological environment, 3) deep underground structure, 4) strong motion observation, and 5) evaluation of earthquake disaster.Our research results are:・ We have obtained a few deep-boring data to a depth of about 4000 m. The geological structure shows that the deepest core has a geological time of Miocene (Tertiary).・ We have obtained PS logging data to a depth of about 500 m at several sites. They show spatial variation of P- and S- wave velocity structures.・ We have estimated deep underground structures at several sites by the microtremor exploration method. The basement has S-wave velocity of about 3000 m/s.・ We have carried out a strong motion observation at 15 sites. The data show spatial variation of the seismic response and strong excitation of basin surface waves.・ We have examined the effects of underground structures on seismic motion based on obtained strong motion data. The examination shows an importance of deep underground structures in evaluation of site amplification.・ We have found some relationships between seismic intensity distribution and underground structure.