[S14-P] Poster

[S14-P-02] Structure of Crust and Upper Mantle beneath South China Sea revealed by Surface Wave Tomography

Thi Giang Ha¹, Tien Hung Nguyen¹, Satoru Tanaka², ^○Le Minh Nguyen¹, Yasushi Ishihara², Vinh Long Ha¹, Quang Khoi Le¹ (1.Institute of Geophysics, Vietnam Academy of Science and Technology, 2.JAMSTEC)

The South China Sea (SCS), the largest marginal sea of West Pacific Ocean, is located in the area of plate triple-junction that connect the Pacific, Eurasian, and Indo-Australian plates. Knowledge of the 3D crust and upper mantle structure is essential to improve our understandings of the geodynamical regimes and tectonic evolutions in this region. Based on the updated seismic recordings recorded by broadband stations from cooperation between Institute of Geophysics, Vietnam Academy of Science and Technology (IGP-VAST) and Japan Agency for Marine-Earth Science and Technology (JAMSTEC) and some others stations from IGP-VAST's seismic network and international networks, we calculated more accurate group velocity dispersion curves of fundamental mode Rayleigh wave with periods from 10 s to 200 s by applying the multiple filter technique for earthquakes occurred around the SCS from 2000 to 2016. We performed the tomographic maps with the lateral resolution of 5x5 degree over the study region. Our tomographic results for Rayleigh wave at periods of 15s, 20s, 30s, and 50s showed that the group velocities in the deep seas are greater than in the shallower seas and lands, it implies that the thicknesses of crust in the deep seas are relatively shallow. However, at the periods of 80s and 120s, the low velocities are present in the Philippine and Java Trench where a lot of active volcanic eruptions exist. The 3D shear wave velocity results revealed that the crustal thickness is ranging from 10 km to 25 km. The lithospheric thickness beneath SCS is about 65-80km, it is relatively shallower than surrounding areas. The prominent low velocity zones (LVZ) exist at the depths of 70km - 200km beneath the active volcanic regions, such as Hainan island, Hon tro vocano (East Vietnam Sea), Andaman sea, Sunda shelf, southern Indochina, Sulawesi, Celebes. The LVZs provide greater thermal support suggesting that these anomalies are the sources of the volcanic rocks in this study area.