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 2

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.

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震度7が制定される前にも震度7相当の揺れは何度か経験している。 武村雅之・他「明治以後の内陸浅発地震の被害から見た強震動の特徴 ―震度VIIの発生条件―」(地震1998) https://t.co/AuRdNlKRt9
武村雅之・他/明治以後の内陸浅発地震の被害から見た強震動の特徴―震度VIIの発生条件― https://t.co/GPDDmELM8H 武村雅之/強震動予測に期待される活断層研究 https://t.co/k6i5i3iO7q
例えば明治以降で震度7程度の揺れとなった地震では地盤の影響が揺れの大きさや被害に効いたようだというのが活断層研究28号の武村論文 https://t.co/2cvoCSfGau 元は地震の武村・他論文 https://t.co/GPDDmELM8H
福井地震以前も以後も震度7相当の揺れはあったけど、なぜ大きく揺れたかを説明するのは簡単ではないっぽい(熊本も説明するのは簡単ではなさそう)。 武村雅之・他「明治以後の内陸浅発地震の被害から見た強震動の特徴」(地震,1998) https://t.co/GPDDmF3nxh
いわゆる活断層と強震動の関係は武村さんの2008年の考察がよいまとめ(活断層学会の28号特集号) https://t.co/r2ShXyRw2F 濃い地震学の話は武村さんたちの1998年の地震の論文(明治以降の震度7について) https://t.co/GPDDmELM8H
内陸地震で震度7相当の揺れがあった事例のレビューは例えば武村・他(1998)の「地震」の総合報告がよくまとまっていると思います https://t.co/GPDDmELM8H
@mkatolithos オリジナルの論説はこちら/武村・諸井・八代「明治以後の内陸浅発地震の被害から見た強震動の特徴-震度VIIの発生条件-」地震2, v50, 485-505,1998. https://t.co/GPDDmELM8H 

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