Abstract
We construct the subsurface fault structure using balanced cross section based on the observation of the stratal deformations around fault outcrops. These fault outcrops were found in the Shimosekita area on the active fault zone along the western margin of the Kitakami Lowland, northeast Japan. Pliocene-Pleistcene Mitusawagawa Formation thrusts over the terrace deposits beneath the small fault scarp on the lowland (F1 fault). Miocene to Pliocene strata thrust over Mitusawagawa Formation on the mountain front (F2 fault). Uplift width of the hanging wall of F1 fault was 30 meters. The hanging wall structure of F2 fault was kink fold with overturned forelimb. Our analysis with a balanced cross section suggests F1 fault with a detachment depth being 20 meters. On the basis of the comparison with the seismic reflection profile at the Ishidoriya area, we propose that a distance between the fault on the mountain front and the frontal fault on the terrace surface may be controlled by a depth to the detachment underneath.
