Comprehensive investigation of earthquake damage due to the 2003 Northern Miyagi earthquake

2003年7月26日，一场中等规模的内陆地震（里氏6.4级）发生在旭山弯曲以下的浅层。地震前震、主震和最大余震在一天内连续3次录得JMA强度为6级。由于这次地震，898所房屋完全被毁，2183所房屋部分被毁。还产生了液化和滑坡。受伤人数达674人（重伤50人），许多人被迫在疏散现场度过余生。在本研究中，研究了建筑物损坏、地面损坏和人员损坏的原因。对地震断层和浅层地质构造的破坏情况进行了地质调查。作为一项多领域协同开展的地震防灾综合调查，开展了地震震害调查和地震断层/地壳结构调查。在地震损伤调查方面，主要介绍了研究成果；1)地震动与破坏的关系；2)与以往地震破坏的比较研究；3)结构与土壤破坏；4)人的破坏与生活障碍。主要结果之一是，从问卷烈度中发现，部分地点的地震烈度为7级，结构损伤随建筑房屋施工时间的延长而减小，但内室损伤不明显。在地震断层/地壳结构调查方面，介绍了地震断层/地壳结构调查的研究成果；1)基于地震反射和地形测量的地震断层调查；2)基于余震观测的浅层地质调查；3)基于GPS的震后地壳运动观测；4)基于强震观测的地质构造调查。主要成果之一是在苏山东缘发现了一条西倾的新断层，其延伸范围与余震观测估计的地震断层一致。结果表明，此次地震不是由被发现为活动断层的旭山弯曲引起的，而是由未被认定为活动断层的地质断层引起的。少

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 … More 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