Recent activities of the Kokura-higashi fault, northeast Kyushu, Japan

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The recent activities of the Kokura-higashi Fault, northeast Kyushu is investigated on the basis of the interpretations of aerial photographs, field surveys, leveling of topographic profiles and trenching surveys.<BR>The Kokura-higashi Fault extends with a NNE-SSW trend for about 17km and the fault tra c e is straight. The vertical component is upthrown on the west side: about 3m on the L surface younger than 25ka, and 5-10m on the H surface older than 140-150ka. These fluvial terrace surfaces show cumulative vertical offsets. The fault plane dips steeply westward and the striations are plunging to the south at an angle of 10-30°. The Kokura-higashi Fault has repeatedly moved in the late Quaternary with predominantly right-lateral movement. The average slip rate of the fault is over 0.1 m/ky (class B).<BR>The most recent faulting occurred around the early BC 2<SUP>nd</SUP>century. The timing of the penultimate faulting event is ca.10,000yBP. If the average recurrence interval is over 9,000yrs, it is not likely that the fault will generate a large earthquake in the near future. The ground surface might be vertically dislocated about 1.7m by reverse slip associated with the past faulting. The net-slip should be several times as large as the reverse slip, taking the right-lateral movement into account.