The Kokura-Higashi fault in Kita-Kyushu City and the surrounding topography

概要

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An active fault, named Kokura-Higashi fault, runs from the eastern and the southern parts of Kokura city with clear fault topography. The fault is considered to cause great earthquakes in the vicinity of the city. By the observation of the aerial photographs and by the investigation on the subsurface geology, the followings become clear. 1. Fluvial terr aces exist along this fault. The gravels which constitute these terraces are very reddish and deeply weathered. Thus, the author renamed them as the old terraces. Terraces lower than those are renamed as new terraces in this paper. 2. The age of the old terrace is at least older than 130 thousands years. 3. Almost all the old terraces are covered with the Aso-4 tephras. 4. The old terraces are all displaced by this fault. In Oba t ake, the gravel constituting the old terrace come in contact by fault with clay which lies under the gravel. The new terrace distributing at the southern extremity is not displaced by the fault. 5. The displacements of the old terrace is 3-11m, and the western side of the fault is uplifted. The amount of displacements increase to the south along the fault and decreases at the southern end. 6. The average slip-rate of the fault is 0.023-0.085m/1000y.
Japanese Society for Active Fault Studiesの論文