1998 rupturing and paleoseismicity of northern Shizukuishi-bonchi seien fault

Authors: Takashi Azuma, Yasuo Awata, Toshikazu Yoshioka and Yuichiro Fusejima

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Abstract:We excavated two trenches on Shinozaki earthquake fault, the surface rupture generated by the 1998 earthquake in northern Iwate Prefecture, in order to clarify the underground structure and previous activities of the fault. A 1 m-wide west-dipping fault zone was exposed beneath the 1998 flexure scarplet. It is inferred that at least one faulting event occurred in the period between about 800 B.C. and 1,300 A.D. from ¹⁴C ages of both the layers that were deformed and not deformed by the faulting prior to the recent rupture. The vertical displacement in this period is estimated to be two or three times as large as that of the 1998 rupture.