Abstract
In this paper, we describe distribution and activity of the Nanshozan active fault group (F1, F2 fault) in detail, based on geomorphic feature and surface geology (Plio-Pleistocene Siwa Formation), including the active reverse fault passing through the first outcrop of the flexure (F3 fault). The Miocene strata have been thrust over the Siwa Formation along the mountain front (F1 fault). The F2 fault deforms fluvial terraces in the footwall of the F1 fault. Deformations of fluvial terraces and arrangement of valley spread of alluvial terraces (L2 surface) provide that the F3 fault runs through east side of the hills on the footwall of the F2 fault. Distribution of fluvial terraces indicates that the F1 fault has been inactive since the middle Pleistocene (H surface). Structure of the Siwa Formation indicates that the F2 fault has been formed since the middle Pleistocene (upper Siwa Formation). Studies of the surface folding and faulting of the fluvial terraces indicate a late Pleistocene vertical offset rate of 0.3 m/k.y. at the F2 fault and 0.05 m/k.y. at the F3 fault. Comparison of vertical offset rates of fluvial terraces provides that the primary fault activity is on the F2 fault.
