Japan Geoscience Union Meeting 2015

Presentation information


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

[S-CG57] Structure, evolution and dynamics of mobile belts

Wed. May 27, 2015 2:15 PM - 4:00 PM A06 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hiroshi Sato(Earthquake Prediction Research Center, Earthquake Research Institute, The University of Tokyo), Koichiro Obana(Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology), Takuya NISHIMURA(Disaster Prevention Research Institute, Kyoto University), Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Aitaro Kato(Graduate School of Environmental Studies, Nagoya University), Jun Muto(Department of Earth Sciences, Tohoku University), Katsushi Sato(Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University), Shuichi Kodaira(Institute for Research on Earth Evolution Japan Agency for Marine-Earth Science and Technology), Takeshi Sagiya(Disaster Mitigation Research Center, Nagoya University), Tatsuya Ishiyama(Earthquake Research Institute, University of Tokyo), Makoto MATSUBARA(National Research Institute for Earth Science and Disaster Prevention), Yasutaka Ikeda(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Chair:Eiji Kurashimo(Earthquake Research Institute, the University of Tokyo)

3:15 PM - 3:30 PM

[SCG57-05] Onshore-offshore deep seismic profiling across the Toyama basin: 2014 Kahoku-Tonami seismic survey

*Tatsuya ISHIYAMA1, Hiroshi SATO1, Naoko KATO1, Eiji KURASHIMO1, Shigeru TODA2, Shin KOSHIYA3, Kenta KOBAYASHI4, Tetsuo NO5, Takeshi SATO5, Shuichi KODAIRA5, Kazuya SHIRAISHI5, Motonori HIGASHINAKA5, Susumu ABE1, GROUP FOR 2014 KAHOKU-TONAMI, Seismic survey RESEARCH1 (1.Earthquake Research Institute, University of Tokyo, 2.Aichi Educational University, 3.Iwate University, 4.Niigata University, 5.JGI, Inc)

Keywords:Sea of Japan, seismic source fault, crustal structure, seismic reflection survey, sedimentary basin

We show preliminary results and interpretation of newly obtained deep seismic reflection profiling across Toyama sedimentary basin beneath Tonami Plain, to illuminate crustal architecture and deep to shallow structures of active faults in this region. We deployed 25 m interval offline seismic recorders covering 15 km long onshore seismic line extending from the Kureha Hills to the shoreline and connected with 2.5 km long bay cable. In addition, we deployed denser, 12.5-m-interval off-line recorders across the Tonami plain to the eastern flank of the Hodatsu Mountains to the west to illuminate shallow high-resolution structures and recent activity of blind thrust structures. Seismic signals enhanced by 25-m-interval shots using four vibroseis trucks were recorded by these onshore and offshore recorders simultaneously. Refraction tomography by use of shot records of 100-150 sweeps at about 5 km intervals suggests that P-wave velocity structure traced by the top of Vp 5 km/sec, presumably correlated with top of the pre Neogene granitic basement rocks appears located 5 km below the sea level beneath the Tonami Plain and delineates significant amount of subsidence of this region during Neogene, equivalent to the Toyama trough located to the north. Deep seismic reflection profile indicates that thick basin-fill beneath the Tonami Plain are strongly faulted and folded by moderately dipping thrust faults located both near topographic domain boundaries and underneath flat-lying alluvial plain. Architectures of folded sedimentary units suggest most of these structures are reactivated normal faults originally formed associated with Miocene extension tectonics. These structural characters of sedimentary basin are similar to other sedimentary basins extensively distributed in backarc regions, such as Niigata basin and northern Fossa magna basin. High-resolution seismic reflection profile indicates recent activity of these reactivated structures. Other important contribution from this experiment include that coastal plain along the Sea of Japan beneath the western portion of the seismic line is underlain by previously unrecognized, east-facing monocline and east-dipping thrust faults. In conclusion, these survey results provide great contribution to construct seismic source fault models for Tsunami and seismic hazard estimation.
* Research group for 2014 Kahoku-Tonami seismic survey: Ikeguchi, N., Yamauchi, K., Tanaka, S., Saka, M., Miyagawa, K., Tagami, K., Tsuji, H., Watanabe, S., Ando, M. (Earthquake Research Institute, University of Tokyo), Hidaka, K., Ouchi, K., Yamada, R. (Iwate University), Ono, A., Sato, H., Katori, T., Iida, K., Kokawa, M. (Niigata University).