[S21-5] Attenuation and lithosphere structure

[S21-5-02] Lithospheric structure beneath Thailand as revealed by seismological approach and its future study with Thai Seismic ARray (TSAR)

^○Sutthipong Noisagool^{1, 3}, Kiwamu Nishida¹, Hitoshi Kawakatsu¹, Songkhun Boonchaisuk², Weerachai Siripunvaraporn³ (1.Earthquake Research Institute, The University of Tokyo, Japan, 2.Geoscience Program, Mahidol University, Kanchanaburi Campus, Thailandd, 3.Department of Physics, Faculty of Science, Mahidol University, Thailand)

Seismological methods have been applied to regional seismic data to study the crust and upper mantle structure beneath Thailand. Receiver function and ambient noise tomography reveal the physical characteristic of crust in each terrane. Crustal thickness beneath Thailand increase from west to east with the average crustal thickness of 30.8 km for Sibumasu terrane (SBT), 33.1 km for Sukhothai Arc (SA), 36.2 km for Loei-Phetchabun Fold Belt (LPF) and 38.2 km for Indochina Terrane (IT). All terranes in Thailand have Poisson's ratio (0.24-0.25) lower than the global average (0.27). This suggests that Thailand might underlie by relatively high-grade metamorphic rock and/or abundant in a felsic composition. Surface waves group velocity tomography from ambient noise period 6-20 seconds show low velocities anomalies in IT and SA. In opposite, ST and LPF have a high- group velocity. The similarity of SA and IT support the geological hypothesis that SA was rift apart from IT during the subduction process, thus they have a similar crustal characteristic. From teleseismic travel time anomalies, upper mantle velocity beneath Thailand can be estimated to increase from west to east. The time-to-depth migration of receiver function data shows no significant variation in the mantle transition zone (MTZ) topography and thickness across Thailand. The MTZ thickness is close to global average with values of 245-250 km. The variation of the mantle beneath Thailand is then likely to be confined in only lithosphere but not an asthenosphere. However, it is difficult to examine whether this feature is control by recent activity such India-Eurasia subduction slab or it is controlled by their own lithospheric origin. From the end of February 2017, forty broadband seismometers of Thai Seismic Array (TSAR) will be installed cover area of Thailand. The resolution analysis of surface wave tomography and body wave tomography from this new array will be present.