Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

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

[S-CG61] Ocean Floor Geoscience

Thu. May 24, 2018 10:45 AM - 12:15 PM 302 (3F International Conference Hall, Makuhari Messe)

convener:Kyoko Okino(Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Yokota Yusuke, Yamashita Mikiya

11:30 AM - 11:45 AM

[SCG61-22] Structural characteristics of the subducting Kyushu-Palau ridge around the Hyuga-nada region in Nankai Trough revealed by seismic reflection imaging

*Mikiya Yamashita1, Ayako Nakanishi1, Ryuta Arai1, Gregory F Moore2, Shuichi Kodaira1, Seiichi Miura1, Yoshiyuki Kaneda1 (1.Japan Agency for Marine-Earth Science and Technology, 2.University of Hawaii)

Great earthquakes with tsunamis with recurrence intervals of 100–200 years have occurred along the Nankai Trough near central Japan. Hyuga-nada is located in the western margin of Nankai Trough, where the Kyushu-Palau ridge (KPR) which is remnant arc constructed by backarc spreading in Shikoku Basin is subducting. Recent ocean-bottom monitoring results have also yielded presence of the episodic low-frequency tremor associated with the activity of very-low-frequency earthquakes (VLFEs) at shallow plate interface at the northern end of subducting KPR. It is important to investigate the crustal structure of subducting KPR for understanding the mechanism of VLFEs in Nankai Trough.

Japan Agency for Marine-Earth Science and Technology carried out a dense high-resolution seismic reflection survey over 600 km of line length around the northern end of KPR from Sep. to Oct. 2016 using R/V Yokosuka.

Beneath the accretionary prism where VLFEs are active, we observed the convex structure corresponding to the subducting Kyushu Palau Ridge. The distribution of trench-fill sediments is limited to only the east side of KPR. It is difficult to trace the frontal thrust close to KPR. There is no deformation structure in the trench-fill sediments from the trench axis to the seaward region around KPR. Our results suggest that subducting KPR contributes to the deformation process around the trench axis.
This study is part of "Research project for compound disaster mitigation on the great earthquakes and tsunamis around the Nankai Trough region" funded by the Ministry of Education, Culture, Sports, Science, and Technology of Japan and JSPS KAKENHI Grant Number 16K17824.