Reevaluation of the displacement per event along the Tsukioka fault, central Japan, based on the fault geometry in the shallow depth

Authors: Yasuo Awata and Taku Komatsubara

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Abstract:The displacement per event of the Tsukioka fault, Niigata Prefecture, central Japan is reevaluated considering the shallow geometry of the fault. A 40-meters-deep drilling revealed that the dip of the fault is 25 degrees beneath the flexure scarp on an alluvial fan of 6 ka. The dip of the fault in the deep is reported to be 60 degrees. The flexure scarp with the vertical offset of 3 meters is simulated using the elastic dislocation theory. From this simulation, the fault displacement is estimated to be 5-6 meters in the deep, and decreases toward the surface beneath the flexure scarp. The displacement per event suggests that the Tsukioka and Muramatsu faults compose a single behavioral segment of 30-35 kilometers long and have a recurrence interval of 10 ky.