西南日本外帯南部の完新世地殻変動 (黒潮圏の第4紀古環境特集号)
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概要
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Many great earthquakes have occurred in historical period along the Nankai Trough where the Philippine Sea Plate subducts under the Eurasia Plate. The outer zone of southwest Japan faces the Nankai Trough, and the coastal areas have been uplifted particularly in response to great earthquakes. In this zone, many types of emerged landforms have been developed since at least the late Quaternary. The development of some emerged landforms may be related to the occurrence of great earthquakes in a singnificant way. This paper aims to clarify the tectonic movements during the Holocene through focusing on the evolution of terraces, sea level change based upon the field observation of outcrops and cored samples, and 14C dating.Holocene marine terraces are developed almost throughout the outer zone of southwest Japan, though their distribution is not continuous owing to the existence of bays or straits between peninsulas. The trend of change in elevation of marine terraces is different in each promontory or peninsula. The southern part of the outer zone of Southwest Japan has uplifted during the Holocene in general. But in the mode of tectonic movements, Shikoku and Kii Peninsula have been different from southeastern part of Kyushu. Shikoku and Kii Peninsula have been uplifted by intra-plate earthquakes which have occurred at intervals of one to several hundred years. On the other hand, the southeastern part of Kyushu has been uplifted aseismically by crustal isostacy. The southeastern part of Kyushu lies to the NNW of the north end of Kyushu-Palau Ridge, which had been island arc until the beginning of the spreading of Shikoku Basin. Much minus free air gravity anomaly can be recognized in and around Hyuga Basin, because Kyushu-Palau Ridge, which is composed of light volcanic rock or granite, subducts just under the southeastern part of Kyushu.The difference in the mode of crustal movemant between the southeastern part of Kyushu and Shikoku or Kii Peninsula is caused by the gap of the plate age. The age of the Philippine Sea Plate off the southeastern part of Kyushu is older than 40 Ma, which is younger than 25 Ma off Shikoku or Kii Peninsula. The Philippine Sea Plate off the southeastern part of Kyushu subducts at a larger angle under the Eurasia Plate than off Shikoku or Kii.
- 日本第四紀学会の論文
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