Quaternary Tectonic Map of Japan

Abstract

The Quaternary tectonic map here referred to consists of five maps. Three of these are contour maps showing amounts of Quaternatry uplift and subsidence and the other two show distribution of Quaternary faults and folds.The uplift and subsidence maps are the one given by the team of geomorphologists (Fig. 1), the one by the team of geologists (Fig. 2), and the one complied from the former two (Fig. 3). Fig, 1 shows the present heights of the erosion flat surfaces formed during the latest Tertiary or the earliest Quaternary age. It is assumed that the surfaces were formed not far from the sea level. Fig. 2 shows the present altitudes and the depths of the locations where upper Pliocene to lower Pleistocene marine sedimentary formations crop out or are buried. It is assumed also in this case that the sedimentation took place at shallow depths. Hence, the vertical displacement approximately represents the algebraic total since the beginning of the Quaternary up to the present. The errors derived from these assumptions seem to be smaller than those derived from the roughness of time estimation, which gives the Plio-Pleistocene age from 3 m. y. ago to 1 m. y. ago. In Fig. 1, the amount of uplift can be traced regionally but the amount of subsidence can not be known. In Fig. 2, both amounts of uplift and subsidence can be known but they can be determined only locally. Taking advantage of the two methods, the authors synthesized Fig. 3, which is one of the conclusions of this work.Both of the faults distribution map (Fig. 4) and the folds distribution map (Fig. 5) are drawn of those faultings and foldings that have deformed sedimentary beds and terrace surfaces since upper Pliocene age. Faults more than 1km in length and folds 500m to 30km in a wave-length are selected.Generally speaking, mountain districts have been uplifted, while lowlands have been subsided. The maximum uplift of about 1700m is found in the Central Ranges, and the maximum subsidence of about 1400m in the Kanto Plain (Fig. 3). It is concluded that the present reliefs of the Japanese Islands are largely due to the Quaternary tectonic movements. The regional trend of fold-axes and strike of faults shows a characteristic pattern (Figs. 4 and 5). The Japanese Islands may be divided into some tectonic provinces by the intensity and nature of the Quaternaty tectonic movements.