南関東・西南日本外帯の地震性地殻変動区に於ける巨大地震の再来周期

Abstract

The seismic crustal movement on the south Kanto district and the Philippine Sea coast of southwest Japan is characterised by the chronic (in the interseismic period) and acute (at the earthquake) tiltings with reverse sense. The accumulation of these tiltings in geological time scale explains the topographic features on the coast such as tilted terraces. The value “d”, which is defined as the ratio of the subsidence in the interseismic period to the coseismic upheaval, was expressed by two independent linear functions of recurrence interval T of series of great earthquakes. The coefficients of these functions are determined by the data of precise levellings and the heights of coastal terraces in the late Quaternary period. Then, the d and T can be determined on the cross point of the two lines which represent the above two functions. This scheme (called d-T diagram) was applied to the Seismotectonic areas of the southern Kanto and the outer arc of the southwest Japan. The results of T obtained are almost in concordance with the intervals of great earthquakes inferred from the historical documents and the rates of convergence of the Philippine Sea plate under the southwest Japan. It was also shown that the d-T diagram can be used as a tool of earthquake prediction taking an example of the Tokai region.