福岡県宗像市池田において発見された活断層露頭

概要

論文の詳細を見る
A new outcrop of a reverse active fault was observed at Ikeda, Munakata City, Fukuoka Prefecture. Late Quaternary fluvial terraces in this area are divided into five levels: Ikeda I terrace to Ikeda V terrace in descending order. Ikeda III Terrace, near the outcrop, is covered with a loamy soil and aqueous silt. Kikai-Tozurahara tephra (95ka) is contained at the middle of the silt. We estimate that the Ikeda III terrace was formed at approximately 100ka. The strike and dip of the fault plane are N20°W and 28°W, respectively. Terrace gravels (Ikeda III terrace gravel), Ikeda Formation (Paleogene) and Kitazaki Granodiorite (Cretaceous) in this outcrop were deformed. The displacement of terrace gravels on this thrust is about 3.2m in the vertical component. From the approximate age of the terrace and the vertical displacement of active faults, the average long-term vertical slip rates is estimated to be 0.03mm/yr. This outcrop overlaps with geologic boundary fault and there is reactivity along the scar of the geologic boundary fault between the Paleogene and Mesozoic basement rocks.