Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS08] Geopark

Mon. May 27, 2019 3:30 PM - 5:00 PM 103 (1F)

convener:Takayuki Ogata(Disaster Prevention Research Center for Island Regions, University of the Ryukyus), Tatsuto Aoki(School of Regional Development Studies, Kanazawa University), Noritaka Matsubara(Graduate School of Regional Resource Management, University of Hyogo), Keiichi Tadokoro(Research Center for Seismology, Volcanology and Earthquake and Volcano Research Center, Nagoya University), Chairperson:Takeyuki Ueki(Faculty of Risk and Crisis Management, Chiba Institute of Science), Marekazu OHNO(Unzen Volcanic Area Geopark promotion office), Takayuki Arima(Department of Tourism Management, Faculty of Economics, Teikyo University)

3:30 PM - 3:45 PM

[MIS08-01] Normal faults observed in the Yonaguni-jima Island, Okinawa Prefecture, southwestern Japan

*Makoto Otsubo1, Kiyokazu Oohashi2, Takayuki Ogata3, Tadahiro Shibata4 (1.Geological Survey of Japan, 2.Yamaguchi University, 3.University of the Ryukyus, 4.Agency for Cultural Affairs)

Keywords:Backarc basin, Normal fault, Okinawa Trough, Quaternary, Ryukyu Arc

Yonaguni-jima Island, Okinawa prefecture is an island located at the westernmost tip of Japan and belongs to the Southern part of the Ryukyu arc. In Yonaguni-jima Island, many normal faults cut the Miocene Yaeyama Group and the Quaternary Ryukyu Group to make the diamond island shape. The fault found at the Sanninudai located in the southeastern part of the Yonaguni-jima Island has all parts of the fault zone; fault gouge part, fault damage zone, wall rock zone. The fault found at the Sanninudai can be activated by the stress field similar to the one in the Okinawa Trough (active back arc basin). Our results indicate that the stress field in the Yonaguni-jima Island may be different from the one in island part of the South Ryukyu arc (e.g., Miyako-jima Island and Ishigaki-jima Island). The relationship between the width of the fault zone and the length of the fault and the relationship between the total displacement and the width of the fault core are similar to them of the typical characteristics of faults. Based on our results, we discuss the possibility that the fault found at the Sanninudai is a suitable site to understand the crustal dynamics (back arc opening) of subdaction zone.