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Regional differences of the crustal movements and the duration of the more active tectonics during the Holocene time in the Ryukyu Islands

琉球群岛全新世时期地壳运动的区域差异和较活跃构造的持续时间

基本信息

批准号：
02452297
负责人：
KAWANA Toshio
金额：
$ 2.75万
依托单位：
University of the Ryukyus
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

Ryukyu Islands are an island arc, situated between Kyushu and Taiwan. The Philippine Sea plate has subducted under the Eurasia plate at the Ryukyu Trench, and the Okinawa Trough has rifted in the Quaternary period ; the Ryukyu Islands have been stressed by the subduction of the Philippine Sea plate and the expansion of the Okinawa Trough. Consequently, the Ryukyu Islands have demonstrated the active island arc in the Holocene time. On the other hand, the Ryukyu Islands are surrounded by coral reefs so that the emerged Holocene reefs are dated by using of the C-14 method for unaltered aragonitic fossil corals. In addition, tsunami deposits which consist of Holocene corals can be dated by the same method. These tsunami deposits have been transported to the Ryukyu Islands probably due to submarine earthquakes. Following islands are selected to investigate in this study : Amami, Toku, Okinoerabu, Okinawa, Iheya, Izena, Tokashiki, Zamami, Aka, Kume, Tonaki, Miyako, Tarama and Yaeyama Islands. On the basis of coastal geomorphology of limestone shores and many dates of fossil corals in these islands, the following results may be summarized.1. The eustatic sea-level fall occurred 4200 and 3000 years BP.2. Holocene tsunamis generated off the South Ryukyus about 220, 500, 1000, 2000, 2400, 3800 and 4400 years BP. probably caused by submarine earthquakes in the Submarine Deep-Sea Terrace between the Ryukyu Trench and the South Ryukyus.3. The more active tectonics in the Holocene period may have occurred about 1700-2400 years BP. due to the intensive activity of the Philippine Sea plate.4. Regional differences of the Holocene tectonics in the Ryukyu Islands are due to the interaction between the subduction of the Philippine Sea plate and expansion of the Okinawa Trough.

琉球群岛是一个岛弧，位于九州和台湾之间。第四纪菲律宾海板块在琉球海沟处俯冲至欧亚板块之下，冲绳海槽发生裂谷；琉球群岛受到菲律宾海板块俯冲和冲绳海槽扩张的压力。因此，琉球群岛在全新世时期表现出活跃的岛弧。另一方面，琉球群岛周围环绕着珊瑚礁，因此使用C-14法对未改变的文石珊瑚化石进行了全新世珊瑚礁的年代测定。此外，由全新世珊瑚组成的海啸沉积物也可以用同样的方法测定年代。这些海啸沉积物被转移到琉球群岛可能是由于海底地震。本研究选择以下岛屿进行调查：奄美岛、德富岛、冲之布岛、冲绳岛、伊平屋岛、伊泽那岛、土城岛、扎美岛、阿卡岛、久美岛、桐崎岛、宫古岛、Tarama岛和八山岛。根据石灰岩海岸的海岸地貌和这些岛屿上珊瑚化石的许多年代，可以总结出以下结果：海平面上升发生在距今4200年和3000年。距今220年、500年、1000年、2000年、2400年、3800年和4400年的全新世海啸发生在南琉球附近。可能是由位于琉球海沟和南琉球之间的海底深海台地的海底地震引起的。全新世时期较为活跃的构造活动可能发生在距今1700-2400年左右。由于菲律宾海板块的强烈活动。琉球群岛全新世构造的区域差异是由于菲律宾海板块的俯冲和冲绳海槽扩张的相互作用所致。