Preliminary report on a new fault exposure of the Senya fault associated with the Rikuu earthquake in 1896, northeast Japan

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An outcrop of the Senya fault, which moved associated with the Rikuu Earthquake in the year of 1896, was newly exposed on the west foot of the Senya hill at the Bodaizawa valley floor, Misato-town, Akita Prefecture (figs. l and 2). The fault dips 30° to the east and extends upward smoothly to the surface of horizontal buried top soil layer. Therefore, displacement of each layer (at least younger than layer II) on this thrust fault is about 1.2m in the vertical component, which is identical with the amount of height of the fault scarp (fig.4), this faulting event is recognized as a last event of the Senya faulting.<BR>This new fault exposure and the result of interpretation of the cadastral map (fig.3) and air photography revealed that the surface trace of 1896 faulting was convexly curved to the upstream ward in the valley floor. This is explained by assuming that the fault plane dipping toward the mountain is steeper in alluvial deposits than in the basement rock (Matsuda, et. al.,1980), or that many short faults with en echelon structure are distributed beneath the surface in the valley bottom (Imaizumi, et. al.,1989, in fig.5).
Japanese Society for Active Fault Studiesの論文