Minami-Shitaura Fault and Its Displacemements

Abstract

Minami-Shitaura fault is an almost vertical fault and 60km south of Tokyo, trending WNW to ESE across the Miura Peninsula. The upper Miocene Hatsuse formation shows a flexure along the fault, in which the southern side of the fault subsided about 500m relatively and a fault plane, along which the same side was uplifted about 250m relatively to the northern side. If we give appropriate absolute ages to four horizons in the middle and upper Pleistocene formations, we can obtain the rates of displacements as 10 to 30cm/103 years, in which the southern side has been uplifted relatively. If we assume the uniform rate back to the time when the faulting changed from subsidence to uplift of the southern side, the time should be one or two million years ago. The rate of right-lateral displacement seems to have become to predominate far over the rate of vertical one at least since the late Pleistocene, on the basis of the offset of stream courses, ridges, and terrace scarps.