1974年伊豆半島沖地震の地震断層

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1974年伊豆半島沖地震調査概報The Izu-Hanto-oki earthquake of May 9, 1974, magnitude 6.9, occurred near the southern tip of the Izu Peninsula. Thirty people were killed, and 100 injured, and more than 2000 houses were destroyed or damaged. Surface fractures appeared in the meizoseismal area along some of the fault lines trending northwest, and displayed right-lateral strike-slips (Fig. 1). The major surface break, the Irozaki-median fault, is about 5.5km long and displaced 45cm right-laterally with a 25cm upthrown relative to the NE side (Fig. 4). The observed fault planes were nearly vertical or slightly inclined to the south, with fault striations plunging 27°~30° to the southeast (Fig. 5). The maximum pressure axis and tension axis of the crustal stress inferred from the fault geometry and the sense of the displacement were nearly horizontal in a N-S direction and in a E-W direction, respectively (Fig. 6).
東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所,東京大学理学部地球物理学教室の論文