| Budget Amount *help |
¥3,500,000 (Direct Cost: ¥3,500,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
Backarc side of Northern Honshu have experienced extensional deformation in early Miocene, associated with the opening of Sea of Japan. Subsequently, since the Pliocene shortening deformation, perpendicular to the arc, has been prevailed with fault reactivation of normal faults as reverse faults. In this study, we made geologic balanced cross sections of the volcanic arc, mainly based on seismic reflection sections. In the Kitakami River Valley zone, we revealed the amount of Miocene extension and later contraction using industry seismic data and obtained seismic reflection data acquired by Earthquake Research Institute (ERI), the University of Tokyo (Kato et al., 2006). To estimate the amount of horizontal shortening, seismic reflection data across the fold-and-thrust belts of northern Honshu, acquired by ERI, were reprocessed, such as the eastern boundary fault of Yokote Basin (Sato et al., 2006 ; Kagohara et al., 2006), the western boundary fault of the Kitakami low land (Kurashimo
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et al., 2006), eastern boundary fault of the Shinjo basin (Sato et al., 2006), and eastern boundary fault of the Shonai plain (Kato et al., 2006).
It is clearly demonstrated by seismic sections that the style of shortening deformation of the backarc sediments is marked by thin-skinned tectonics with shallow detachment fault developed in Miocene marine mudstone. The deeper extension of reverse faults are commonly traced to high to moderate angle reverse faults, originally formed as normal faults, suggesting thick-skinned tectonics. Extensional structures associated with the Miocene rifting are well preserved in the present Northern Honshu and controls the subsequent shortening deformation. Along the Mizusawa-Honjo section of northern Honshu, the total amount of Miocene extension in the volcanic arc curst on land is calculated to be 37km and amount shortening is to be 14km. Most of the shortening deformation is consumed along the Sea of Japan coast and the amount of shortening along the eastern margin of the Northern Honshu rift is only 1km. Less
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