Trenching study of the Kego fault, at Osano, Dazaifu City, Fukuoka Prefecture

概要

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The Kego fault extends from Fukuoka City to Chikusino City, in North Kyushu. Recently, we made a trench across the fault at Osano, Dazaifu City near the southern end of the fault zone. The fault<BR>exposed was a west-dipping reverse fault, though the striation on the fault plane suggested larger strike-slip component. The late Quaternary strata younger than about 32,000 years B. P. on the Mesozoic granite were displaced about 65cm with the western side upthrown at the basal part. Deformation with steep flexures partly overturned in the middle and a gentle warping in upper horizons was dominated on the upward extension of the fault. The vertical displacement, about 65cm, of ca.32,000 years old strata, indicates about 0.02mm/year in an average rate of vertical displacement of the fault. The following two events were recognized, which explain the observed fault-related structure. Event 1 between ca.1,500 yr. B. P. and ca.16,000 yr. B. P., in which about 40cm difference in height was produced on the uppermost formation. Event 2 between. ca.25,000 yr. B. P and ca.32,000 yr. B. P., in which the fault moved as much as 25cm in the same sense as Event 1.
Japanese Society for Active Fault Studiesの論文