関東地方の第四紀構造盆地の形成過程に関する一考察

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There are two Quaternary tectonic basins in the Kanto district called the Kanto Tectonic Basin and the Sagami Sedimetary Basin, respectively. The former is extremely large in the Japanese islands and has experienced a very complex tectonism since when it originated. Along the western margin of the Kanto Tectonic Basin, there are several dissected hills consisted of the lower Pleistocene fluvial gravels and shallow marine deposits, and they gently incline to the northern area of the Omiya upland which is situated at one of the depressions in the tectonic basin. The lower and middle Pleistocene marine formations, which are almost continuous sucession, make southern slope of the basin at the Boso Peninsula and incline toward another depression in the basin which sites at the northern part of the Tokyo Bay. The Pleistocene marine deposits being more than 1400 m in thickness lie under the ground of the Kanto Plain. The top of these deposits form the upland, 20 to 40 m high, about the center of the basin. From these evidences, it is recognized that a basin building has been continuing during the Quaternary period. The extent of the tectonic basin, however, was not fixed at the present site from the past. It migrated northwestward from southeastern area of the Boso Peninsula and split into some small depressions. The Sagami Sedimentary Basin which sites at southern area of the Kanto district is one of the depressions diverged from the Kanto Tectonic Basin. From many geological and geomorphological data, it is assumed that the Quaternary teconic movements in this area were occasionally active and they were conspicuous at the early stage of the middle Pleistocene and the early stage of the late Pleistocene. At the former stage, sea bottom shallowed and upheaved until the land appeared in the mid area of the Boso Peninsula. Many faults were formed around there during the active period. The mouth of the so-called Paleo-Tokyo Bay which had opened widely eastward was narrowed and driven toward northeast. At the later stage, the environs of the Kanto Tectonic Basin slightly upheaved and some folds and faults were formed. Besides, the west end of the Sagami Sedimentary Basin was extremely uplifted and formed a great fault scarp being more than 230 m in relative height. This fault is called the Kozu-Matsuda Fault which is well known to have removed at the great Kanto earthquake of 1923.
日本地質学会の論文
1977-02-21

関東地方の第四紀構造盆地の形成過程に関する一考察

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