関東地方の島孤変動 : 陥没の発生と将棋倒し法則に関する諸問題

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The gist of the present paper is itemized below. 1. The outline of the sedimentary basin of the Kanto plain was determined by the collapse basin of the formative stage of the Late Pliocene Kurotaki unconformity and the collapse basin of the Early Pleistocene Minamitama stage (Fig. 2). 2. Due to the fractures of NE-SW and NW-SE trends that began to develop during the period from the Nagahama stage at the end of Early Pleistocene to the Naganuma stage of the early Middle Pleistocene, the uplands and alluvial plains were taking form macrotopographically in the Kanto plain and they became distinct during the Late Pleistocene as seen today (Fig. 3). 3. Collapse basins of the Kurotaki and Nagahama stages were formed along the fractures that were caused by the upheaval of the area centering around the basins (Fig. 1, B). 4. Collapse or relative subsidence of lowlands in the Nagahama stage and since the Shimosueyoshi stage procceded as the pre-existent fractures were reactivated with the regional upheaval (Fig. 3). 5. The law of the shogi-daoshi structure (sedimentary imbricate structure) is essentially a unidirectional shift of the thickest portion of a group of formations within one basin (Fig, 4). This structure is interpreted as a result of reactivation of fractures which developed when the basin was formed (Fig. 1,B). 6. When plural sedimentary basins whose longer axes run parallel are formed, the formations in each basin may present a shogi-daoshi structure of such a type as mentioned above, and occasionally this structure is found to involve the whole basins (Fig. 5). The occurrence of the shogi-daoshi structure can be classified into two kinds. One is the case where plural basins are formed simultaneously. This kind is noticed in many geosynclines (Fig. 5). The other kind is the case when the shogi-daoshi structure occurring within one basin proceeds into another basin in front of the first basin (Fig. 6). However, this kind is not fully investigated yet and it requires further study. 7. A general direction of the shogi-daoshi structure was from the continental side toward the Pacific side during the Paleozoic〜Middle Mesozoic period, and from the Pacific side toward the continent since the Middle Mesozoic to the present. And, as pointed out by Yano (1980), the direction of the shogi-daoshi structure in the stage of the Green Tuff geosyncline and that in the stage of the Island Arc disturbance are intersecting at right angles, and they intersect the principal axes of the basins at right angles. It is possible, however, that the principal axes of the basins have changed their directions later.
日本地質学会の論文
1981-03-30

著者

藤田至則
新潟大学積雪地域災害研究センター

関東地方の島孤変動 : 陥没の発生と将棋倒し法則に関する諸問題

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