著者
武村 雅之 諸井 孝文 八代 和彦
出版者
公益社団法人 日本地震学会
雑誌
地震 第2輯 (ISSN:00371114)
巻号頁・発行日
vol.50, no.4, pp.485-505, 1998-03-13 (Released:2010-03-11)
参考文献数
96
被引用文献数
1 4

Two types of earthquakes have occurred in and around Japan, which have resulted in severe damages. They are inter-plate earthquakes in subduction zones around the Japan Islands, and intra-plate earthquakes in the upper crust beneath the mainland of Japan. The faults associated with intra-plate earthquakes usually exist within a depth of 20km. Six intra-plate earthquakes causing a toll of more than 1, 000 lives have occurred since the end of the 19th century. The faults responsible for these events were estimated from the trains of surface fault breaks and the measured crustal deformations. Three intra-plate earthquakes with magnitude M larger than 7, which killed more than 200 people, have also occurred in the same period. Their causative faults have also been estimated. Many reports of damage surveys of the above nine intra-plate earthquakes were examined to investigate conditions necessary for generating strong ground motion with seismic intensity I=VII (very disastrous) in the Japan Meteorological Agency (JMA) scale, and to elucidate characteristics of strong ground motion with I=VII. According to the original definition of the JMA scale, I=VII (very disastrous) corresponds to “Collapse of more than 30% of wooden houses”. The data on damage to wooden houses for the nine events show that the area of I=VII extends up to 5km on both sides of the fault in the case of faults through mountainous region. On the other hand, in the case of earthquake faults lying underneath basins, where sediments have accumulated from the Late Pleistocene to Holocene, the area of I=VII extends over a wider area and occasionally fills the whole basin. The ground condition is seen to be an important factor in generating strong ground motion with I=VII. A similar result is obtained from an examination of the 1923 Kanto earthquake near source region with the thrusting fault at a depth shallower than 20km. The Kanto earthquake is one of the typical disastrous inter-plate earthquakes in Japan. The data on the directions of simple bodies that have overturned and collapsed wooden houses in the proximity of earthquake faults indicate that systematically larger ground motions occur in a direction normal to the strike than parallel to it irrespective of the type of faulting. The effective periods for these simple bodies and wooden houses are estimated to be in the range of 0.3sec to 1.5sec. These results indicate that the dominant strong ground motion in the direction normal to the strike plays an important role in generating the severe damages in regions hit by intensity I=VII.
著者
武村 雅之 加藤 研一 八代 和彦
出版者
日本建築学会
雑誌
日本建築学会技術報告集 (ISSN:13419463)
巻号頁・発行日
vol.2, no.3, pp.269-274, 1996
被引用文献数
1 2

Historical damages due to intermediate and deep focus earthquakes are reviewed on the basis of earthquake catalogs in past 100 vears. These earthquakes occurred at North-Eastern and South-Western parts of the Japan islands at a rate of 4 to 5 times per year. The earthquake catalogs indicate that only the intermediate depth earthquakes, with magnitude exceeding 7.5 and focal depth shallower than 150 km, caused destructive damages. However, the damage rank is lower than the typical interplate earthquakes along the Japan trench such as the 1968 Tokachi-oki earthquake (M=7.9).
著者
加藤 研一 武村 雅之 八代 和彦
出版者
日本建築学会
雑誌
日本建築学会構造系論文集 (ISSN:13404202)
巻号頁・発行日
vol.64, no.521, pp.33-40, 1999
被引用文献数
5 4

The excitation strengths of high-frequency strong motions from intermediate depth earthquakes (IDE) are investigated from the peak ground accelerations (PGA) of 13 events occurring at Eastern Japan. 13 shallow earthquakes at the same region are also analyzed for comparison. The observed PGA's from IDE's show systematically larger amplitude than the empirical average obtained from shallow events by a factor of 1.6. These deviations show regional variation: the IDE's at the Hokkaido and the Kanto regions excite larger PGA than those at the Tohoku region. It is concluded that the focal depth is a key parameter to control the amplitude of PGA rather than focal mechanism and/or fault type.