Relationship between the tectonic relief and the subsurface geological structure related to strike-slip displacement: a case of the en échelon faults

Abstract

This paper clarifies the relationship between the tectonic relief and the subsurface geological structure under several meters, and also we consider the structure in three dimensions and the tectonic formation process around the strike-slip fault. The study site is Mimayano district in the south-central part of the Gero fault of the Atera fault system, which is one of the prominent faults in central Japan. We have carried out topographical and geological explorations, drawing up of detail counter map, trench excavation investigation, and ground penetrating radar exploration. The results of these investigations show that the tectonic relief and the shallow geological structure have the Riedel shear structure as the order from several meters to dozens of meter. We conduced that the strike-slip displacement on the Gero fault in the basement rocks formed the right-handed Riedel-shear type faults in soft-sediment overlying the rocks. A small-scale tectonic relief as linear scarps, narrow depressions in right-stepping en échelon, and pressure ridges of several meters in wave-length are distributed on the ground surface along the arrangement of the Riedel-shear type faults.