Abstract
The Ushikubi fault, located along the boundary between Toyama and Gifu prefectures, northern central Japan, is one of the longest active faults in Japan. We performed morphological and structural analyses based on geological survey of the central part of the Ushikubi fault. As a result, we identified the geometry and movement history of this fault. Along the Ushikubi fault, multiple fractures are branched, bent, paralleled, slanted intersection, and form a pretty complicated shear zone. Particularly in the central part of the study area, the multiple fractures form a strike-slip duplex. The geometry of the shear zone indicates it was originated from a sinistral strike-slip fault. In addition, the observation of polished sections and thin sections supports the result. In this study, the shear zone along the Ushikubi fault is called the Ushikubi shear zone. This shear zone was generated as a sinistral strike-slip fault in Late Cretaceous time, and has been inversely reactivated as the Ushikubi active fault.
