Studies on Landslide and Unconformity, Sendai District, Northeast Japan

Abstract

In the landslide area of Sendai district, Miyagi Prefecture, the Pleistocene formation of the Aobayama stage covers the underlying Pliocene and Miocene deposits; and unconformity is observed in the formations of this area. The degree of unconformity in the landslide area is determined by the greatness of the geologic movements. We examined the compressibility of many specimens of sedimentary rocks gathered from the neighborhood of the unconformable part which forms the boundary between the overlying and the underlying strata in the formations of this area. A classification scheme illustrates three grades and two types of compressibility which have resulted from chemical and mechanical weathering. From this, a study was made of the influence of crustal movement upon landslides; besides, the volume of sedimentes was esimated, basing the estimation upon preconsolidation pressure. In conclusion, the mechanism of the present landslide is strongly controlled by the crustal movement which was formed in geologic eras, and a remarkable relation is observed between unconformity and crustal movement which is indicated by fault and folding.