Active faults and neotectonics in and around the southern part of the Tanzawa Mountains and the Oiso Hills in the southern Fossa Magna region are summarized on the basis of new evidences obtained from fault analyses and tephrochronological studies. The active faults in this area can be classified into the following four systems; the E-W Kannawa thrust, the E-W high-angled reverse faults, the NE-SW left-slip faults and the NW-SE right-slip faults. Most of the strike-slip faults have dip-slip components. The Kannawa thrust probably moved during the Middle Pleistocene, and the other faults have been active since the late Middle Pleistocene, under the regional compressional stress field of N-S direction. The accumulation and deformation of the strata in this area have been strongly affected by displacements along the above mentioned fault systems.
