- 東京帝国大学地震研究所彙報 (ISSN:00408972)
- vol.14, no.4, pp.619-631, 1936-12-21
Warping of the slopes of the Taga and Yugawara volcanoes (lower Pleistocene) caused subsidence of the Tanna and Tasiro basins and at the same time elevation of the area between Kuro-dake and Nirayama. Later, this district was affected by the Tanna fault. The block on the western side of the fault was displaced about 1 km horizontally southward for the greater part of the fault line, and was elevated about 100 meters or more in its southern part, relatively to the block on its east. The fault displacement that occurred at the time of the earthquake of 1930 is similar in character to the above-mentioned displacement that occurred in geological times. The fault displacement itself is not the sole cause of the origin of the Tanna basin. This basin was formed chiefly through down-warping of the volcanic slope. As a result of the fault displacement, the topography of the basin became somewhat more complex than it had been before.