SATO Hiroshi Tokyo University, Earthquake Research Institute, Associate Professor, 地震研究所, 助教授 (00183385)
KAGAMI Hiroshi Hokkaido University, Graduate School of Engineering, Professor, 工学研究科, 教授 (70016476)
SAKAI Yuki Tsukuba University, Institute of Engineering Mechanics and Systems, Associate Professor, 機能工学系, 助教授 (10235129)
YAMANAKA Hiroaki Tokyo Institute of Technology, Interdisciplinary Graduate School of Science and Engineering, Associate Professor, 大学院・総合理工学研究科, 助教授 (00212291)
On July 26, 2003, a moderate class inland earthquake (M6.4) occurred at the shallow portion bellow the Asahiyama flexure. Ground motions recorded JMA intensity of 6 for three times in a row within a day by foreshock, main shock, and the largest aftershock. Due to this earthquake, 898 houses were totally destroyed and 2, 183 houses are partially destroyed. Liquefaction and land slides were also generated. Injured persons counted 674(seriously injured 50) and many people were forced to spend life at evacuation site.
In this study, the cause of building damage, ground damage, and human damage has been investigated. Geological survey was also performed for investigating the damage in relation to the seismic fault and the shallow geological structure. As a comprehensive investigation by collaboration of various fields regarding earthquake disaster prevention, the following investigations regarding earthquake damage survey and seismic fault/crustal structure survey were performed.
As for the e
arthquake damage survey, the research achievements are described for the topics on ; 1) relation between ground motion and damage, 2) comparison study to the past earthquake damage, 3) structural and soil damage, 4) human damage and life obstruction. As one of major results, it was found from the questionnaire intensity that the seismic intensity at some locations were 7, and that structural damage decrease with the construction time of the building houses but not the case for the inner room damage.
Regarding the seismic fault/crustal structure surveys, the research achievements are described for the topics on ; l) seismic fault investigation based on seismic reflection survey and topography survey, 2) shallow geological survey based on aftershock observation, 3) postseismic crustal movement observation based on GPS, 4) geological structure investigation based on strong motion observation. As one of major results, it was found from the reflection survey that the new fault with west dip was discovered at the east edge of Sue hill and its extension is consistent with the seismic fault estimated from the aftershock observation. It is concluded that the earthquake was not due to the Asahiyama flexure noticed as an active fault but the geological fault which was not approved as an active fault. Less