Fault Heterogeneity of Inland Earthquakes in Japan
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概要
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Detailed rupture processes of six intraplate earthquakes in Japan, the 1961 Kitamino earthquake, the 1969 GifuKen-Chubu earthquake, the 1974 Izu-Hanto-Oki earthquake, the 1975 OitaKen-Chubu earthquake, the 1980 Izu-Hanto-Toho-Oki earthquake, and the 1984 NaganoKen-Seibu earthquake, are compiled and compared to each other to make clear common features of an earthquake rupture process. The rupture processes are obtained by waveform inversion using strong motion seismograms in previous studies. Five of these rupture processes are also compared with distributions of precisely determined aftershocks. Earthquakes with relatively smooth rupture propagation, such as the 1974 Izu-Hanto-Oki earthquake and the 1961 Kitamino earthquake, represent smoother slip distribution than earthquakes with relatively irregular rupture propagation, such as the 1969 GifuKen-Chubu earthquake and the 1980 Izu-Hanto-Toho-Oki earthquake. It is also recognized that aftershocks of magnitude greater than 4 do not occur in the large slip area. Most large aftershocks take place near the edge of the large slip region and in the small slip region. Aftershocks also tend to cluster near the edge of the large slip region. These results are very consistent with numerical experiments of dynamic rupture, so it is suggested that the relation between aftershocks and coseismic slip pattern obtained in this paper hold generally for earthquake rupture processes. A clear delay of rupture propagation occurs in the large slip area during the 1969 GifuKen-Chubu earthquake: on the other hand, the small slip area in the 1980 Izu-Hanto-Toho-Oki earthquake is characterized by a deceleration of rupture propagation. The large slip area in the former case is interpreted as a barrier which resisted fracturing at first and was broken with a high stress drop. In the latter case, mechanical weakness due to volcanic structure located around the source region, seems to have affected the rupture process. A similar geological condition may have affected the rupture process of the 1978 Izu-Oshima-Kinkai earthquake which occurred about 10 km south of the 1980 Izu-Hanto-Toho-Oki earthquake.日本内陸で発生した6つの地震について,詳細な破壊過程を取りまとめ,それらの相互の特徴及び余震分布との対応等を調べた.取り上げた地震は1961年北美濃地震・1969年岐阜県中部地震・1974年伊豆半島沖地震・1975年大分県中部地震・1980年伊豆半島東方沖地震及び1984年長野県西部地震である.これらの地震については,震源近くで記録された強震計記録の波形インバージョンにより,詳細な破壊過程が解明されている.
- 1990-12-25