Fault model of the 1703 Genoku Kanto Earthquake ( M 8.2)
along the Sagami Trough deduced from renewed coseismic crustal deformation

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Masanobu Shishikura, Shinji Toda and Kenji Satake
Active Fault Research Center, AIST, Tsukuba, Japan

Abstract: The 1703 Genroku Kanto earthquake (M~8.2) that struck the southern Kanto district is thought to be larger than the 1923 Taisho Kanto earthquake (M7.9), but there are, of course, no instrumental observations. To reveal the source fault of the 1703 earthquake, we estimated the amount of vertical crustal movement and the tsunami height by analyzing historical records, shoreline topography and marine intertidal faunas. The Miura peninsula and the Oiso coast were 1-2 m uplifted both by the 1923 and 1703 earthquakes, but the crustal movement on the Boso Peninsula was quite different. The Boso peninsula was steeply tilted northward by 6 m of uplift in 1703, three times larger than the 1923 earthquake. Tsunami heights were also higher in the eastern coast of the Boso peninsula, though the other areas were almost same amount as the 1923 earthquake. Based on these data, we propose the source fault model composed of fault A, B and C. Fault A is an inter-plate fault that ruptured beneath the Miura peninsula and the Oiso coast, which also ruptured in the 1923 earthquake. The steep tilting and large tsunamis in the Boso Peninsula were due to the rupture of faults B and C.

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Figure caption: Coseismic crustal movements during the 1923 Taisho Kanto earthquake and the 1703 Genroku Kanto earthquake, and fault model of the 1703 Genroku Kanto earthquake. Contours are in meters. Data of the 1923 Taisho Kanto earthquake is after Miyabe (1931).

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