Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

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

[S-CG61] Dynamics in mobile belts

Tue. May 28, 2019 1:45 PM - 3:15 PM Convention Hall A (2F)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Toru Takeshita(Department of Natural History Sciences, Graduate School of Science, Hokkaido University), Hikaru Iwamori(Geochemical Evolution Research Program, Japan Agency for Marine-Earth Science and Technology), Chairperson:Naoki Uchida, Takeshi Iinuma

2:15 PM - 2:30 PM

[SCG61-27] Shear wave splitting east off NE Japan based on the S-net data

*Naoki Uchida1, Junichi Nakajima2, Ryota Takagi1, Keisuke Yoshida1, Takashi NAKAYAMA1, Ryota Hino1, Tomomi Okada1, Youichi Asano3, Sachiko Tanaka3 (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions Graduate School of Science, Tohoku University, 2.Department of Earth and Planetary Sciences, Graduate School of Science and Engineering, Tokyo Institute of Technology, Tokyo, 3.National Research Institute for Earth Science and Disaster Resilience)

Keywords:Shear wave splitting, S-net, forearc

We estimated the anisotropy of seismic wave speed by using shear wave splitting data in the offshore area of NE Japan. The analysis was made possible by the deployment of the Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net) by National Research Institute for Earth Science and Disaster Resilience (NIED). We used the waveforms of 421 interplate earthquakes from August 2016 to October 2018 which are selected based on the focal mechanisms of Full Range Seismograph Network of Japan (F-net) operated by NIED and located under the S-net stations (within 35 degree from the vertical). We determined the fast polarization directions and delay times between fast- and slow-shear waves by the cross-correlation method.

The results show that the shear wave splitting tends to have trench parallel fast polarization direction for the region east off Chiba to Hokkaido which is the same with the observations in the land area of the forearc. Since we used earthquakes on the plate boundary, the anisotropy must be located in mantle wedge or forearc crust. The interpretation of the polarization includes the flow-normal fast direction of B-type olivine fabric in the forearc mantle-wedge and cracks aligned in the trench parallel direction due to the present forearc stress-field or fossil structures developed during the formation of the forearc.

Acknowledgements: We used S-net data which is deployed and maintained by NIED.