S-wave Relative Travel Time Tomography for Mantle Structure Beneath East Asia.

East Asia is a tectonically complex area, with earthquakes and volcanism along plate boundaries and within plates. China is located in the Eurasian plate, with the western portion being affected by the tremendous stresses of the Himalayan continental collision, which may be the cause of earthquakes in the continental interior. Interaction between the subducting Pacific plate and the upper mantle has led to the formation of a large mantle wedge, which has been inferred to be the cause of intraplate volcanism in Northeastern China. In order to study this complex region, we conducted S-wave relative travel time tomography to image the velocity structure between 100 - 600 km depth beneath East Asia. We used broadband stations provided by IRIS, F-net from NIED and regional networks in South Korea and eastern China. The relative observations were obtained by applying the multi-channel cross-correlation method in the AIMBAT software (Lou et al. 2013). We carried out checkerboard resolution tests to estimate the reliability of our results. Based on the tomographic results, Datong and Wudalianchi intraplate volcanoes in northeast China do not seem to be related to mantle plume activity, while the Mt. Baekdu does. High-velocity anomalies are detected beneath the Tarim, Ordos and Sichuan basins, stable cratons in China. High velocity anomalies are observed along plate boundaries around the Japanese islands region. These anomalies may show subducting Philippine and Pacific plates. Low-velocity anomalies are revealed beneath the Jeju Island and east of the Korean Peninsula, which are thought to be related to formation of the Jeju Island and the Ulleung basin.