Japan Geoscience Union Meeting 2015

Presentation information


Symbol S (Solid Earth Sciences) » S-CG Complex & General

[S-CG64] Ocean Floor Geoscience

Wed. May 27, 2015 2:15 PM - 4:00 PM A05 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Kyoko Okino(Ocean Research Institute, University of Tokyo), Keiichi Tadokoro(Research Center for Seismology, Volcanology and Earthquake and Volcano Research Center, Nagoya University), Osamu Ishizuka(Geological Survey of Japan, AIST), Tomohiro Toki(Faculty of Science, University of the Ryukyus), Narumi Takahashi(Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology), Chair:Mikiya Yamashita(Japan Agency for Marine-Earth Science and Technology), Tomohiro Toki(Faculty of Science, University of the Ryukyus)

2:15 PM - 2:30 PM

[SCG64-04] P-wave velocity structure in the southern Okinawa Trough

*Azusa NISHIZAWA1, Kentaro KANEDA1, Mitsuhiro OIKAWA1, Daishi HORIUCHI1, Yukari FUJIOKA1 (1.Japan Coast Guard)

Keywords:Okinawa Trough, rifting, marine seismics

The Okinawa Trough is a backarc basin under continental rifting tectonics by subduction of the Philippine Sea plate beneath the Eurasian plate at the Nansei-Shoto (Ryukyu) Trench. The rifting stage varies from north to south along the trough and the southern region is in most evolved stage. We carried out around ten seismic experiments in the southern Okinawa Trough to obtain detailed images of crustal thinning in this region. We shot six lines along several en echelon rifts that characterize the seafloor feature in the southern trough. Each seismic experiment consists of multichannel reflection seismic (MCS) profiling using 240 ch. and 3000 m long hydrophone streamer and wide-angle seismic refraction profiling using ocean bottom seismographs (OBSs) as receivers.

The crusts in the Okinawa Trough roughly have three layers of the upper, middle and lower crust, which is same as an island arc crust. P-wave velocity model beneath the Yaeyama Rift, the deepest rift in the Okinawa Trough, also consists of the three crustal layers. The crustal thickness is more than 10 km and significantly thicker than a standard oceanic crust. Many intrusion signals in MCS records characterize the crust below the rift.