糸魚川-静岡構造線の重力調査(III) : 諏訪湖周辺部のブーゲー異常

概要

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諏訪湖周辺に約400点の重力測定を実施した.諏訪湖は糸魚川-静岡構造線の12kmにおよぶ左横ずれ断層運動により生じた陥没地形であって,陥没量は800mを越える.ブーゲー異常から推定すると,陥没量は1～1.4km,横ずれ量は明確ではないが15～20kmと見積ることができる.The Suwa basin is located in the middle part of the Itoigawa-Shizuoka geotectonic line, the left-lateral displacement of which is estimated as about 12 km from geological evidence. The vertical displacement of the basin subsidence amounts to about 800 m. Another important geotectonic line called the Median tectonic line intersects the Itoigawa-Shizuoka line near the Suwa basin. We define gravity field disturbances associated with these faulting activities in considerable detail by concentrating gravity surveying points on the Suwa basin. We clarify gravimetrically the structure around the intersection of the two tectonic lines. Analysis of Bouguer anomaly indicates that the basin subsidence may exceed 1000 m and the lateral offset amounts to 15～20 km, though the latter is not necessarily clear.
東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所,日本測量協会の論文
1988-03-31