[S-IT16] 地球深部科学

[SIT16-P02] The direction of mantle flow beneath Thailand inferred from shear wave splitting measurements

*Tarudee Autaijaratrasmee¹、Satoru Tanaka²、Kenji Kawai¹、Sutthipong Noisagool³ (1.Department of Earth and Planetary Science, School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan、2.Research Institute for Marine Geodynamics (IMG) Volcanoes and Earth’s Interior Research Center (VERC) Geophysical Research Group, Japan Agency for Marine-Earth Science and Technology、3.Department of Physics, Mahidol University, 999 Phutthamonthon Sai 4 Rd, Salaya, Phutthamonthon District, Nakhon Pathom 73170, Thailand)

キーワード：Mantle flow, Shear wave splitting, Anisotropy, Transverse energy minimization method

We infer the anisotropic properties of the mantle beneath Thailand based on shear wave splitting analyses. The magnitude of anisotropy is quantified by the travel time difference (dt) between the fast and slow shear waves. The fast axis orientation of anisotropic minerals is related to the angle (φ) between the P-wave and the fast shear wave. We made a Matlab code based on the transverse energy minimization method (Silver and Chan, 1991) to infer dt and φ. To validate the code, we compared our results with Yu et al. (2017) result. The graph after minimization, the particle motion, and the fast and slow shear waves before time shift delay time(dt), are the same. So, we applied it to the data from Incorporated Research Institutions for Seismology (IRIS) seismic data for 3 stations in Thailand, Chiang Mai station (CHTO; 18.8140°N, 98.9440°E), Chiang Mai station (CMMT; 18.8128°N, 98.9476°E), and Phuket station (PKDT; 7.8464°N, 98.3230°E). We got preliminary results for CHTO 3 events, CMMT 8 events, and PKDT 1 event as follows: dt_CHTO = 2.98 ± 0.25 s and φ_CHTO = 49.26 ± 4.64°, dt_CMMT = 2.18 ± 0.82 s and φ_CMMT = 79.47 ± 21.25°, and dt_PKDT = 1.93 s and φ_PKDT = -2.15°. But the results are not good enough because the data set was a small size and the phases were not suitable to use the method to find φ and dt. Therefore, we are analyzing the data observed by the Thai Seismic Array (TSAR) Project which are suitable phases to investigate the more detailed anisotropic structure in the upper mantle beneath Thailand. We will show the results and discuss their geophysical interpretation in the presentation.