Neotectonics along the eastern rim of the Nara Basin, central Japan.

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  • 奈良盆地東縁地域の活構造
  • ナラ ボンチ トウエン チイキ ノ カツコウゾウ

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The Nara Basin, the eastern rim of which is bordered by N-S trending faults and flexures, is located in the central part of the Kinki Triangle.<br>The writers have investigated displaced topographies and deformed strata to understand the nature of neotectonics of the area. The findings are summarized as follows.<br>1) Several river terraces distribute widely along the eastern rim of the Nara Basin. They are classified into five according to their age: namely Kokuzoyama, Narasaka, Rokuyaon, Wani and Ichinomoto surfaces in descending order. The deposits of the Ichinomoto surface are dated 18, 410±920y.B.P. (GaK-9709) by 14C method.<br>2) Terraces have been deformed along the Tenri and Narasaka flexures. These flexures are surface expressions of the reverse faults in bed rocks. The average rate of the vertical component of the deformation is calculated 0.07-0.30m/103y. for the Tenri flexure and 0.13-0.17m/103y. for the Narasaka flexure.<br>3) The Tenri flexure occurred after the formation of the Kokuzoyama surface, and simultaneously the Sanbyaku fault, which borders the basin in the west and the mountains in the east, became inactive. This implies that the fault movement migrated from the mountain foot toward the basin in middle Pleistocene.

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