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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS014 Poster presentation 2276 Is there the Amurian plate in northeast Asia Dr. Shuanggen Jin Astro-Geodynamics Center Shanghai Astronomical Observatory, Chinese Aca.Sci IAG Pil-Ho Park The plate tectonics of Northeast (NE) Asia is very complex with diffuse and sparse seismicity in the broader plate deformation zone. Zonenshan and Savostin (1981) firstly proposed the existence of the Amurian plate in NE Asia based on the clear geographical boundary of Kuri-Japan trench and Baikal rift zone, but became diffuse throughout continental northeast Asia. This proposed Amurian plate (AM) is of special interest to constrain the relative motion of the major and minor plate in Northeast Asia and provides a rigorous framework for interpreting seismicity and the kinematics, especially for actively seismic Japan. However, whether it exists or not and its boundary geometry remain controversial, especially the location of the south boundary. Now the increasingly dense GPS networks operated by East Asian countries in this area provide an important tool to investigate plate tectonic movements and to identify the approximate location of plate boundaries. In this paper, the possibility of Amurian plate motion independent of Eurasia is tested rigorously using GPS velocities incorporating block modeling. The test has shown that the Amurian plate is independent of the Eurasian plate motion with statistical significance above 99% confidence level, and the south boundary of the Amuria is along the Yin-Yan Shan belt through to Japan. Keywords: plate tectonics, amuria, gps

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS014 Poster presentation 2277 Crust and upper mantle structure in continental China and its adjacent area from surface wave two-station analysis Mrs. Guixi Yi Information Engineering College Chengdu University of Technology IASPEI Yao Huajian, Zhu Jie-Shou, Robert D, van der Hilst Based on surface wave data recorded by 102 stations in China and adjacent area, we measure interstation Rayleigh-wave phase velocity dispersion data from two-station analysis and finally obtain dispersion curves in the period band 20-120s for 538 independent paths. Dispersion data are then used to invert for 21 phase velocity maps from 20s to 120s with 5s interval in the continental China and its adjacent regions (70-140E, 18-55N). Checkerboard tests show that the lateral resolution is about 3 in central-eastern China and about 5 in western China and adjacent regions. The main results obtained are shown as follows: (1) The spatial distribution of phase velocities in the studied area is significantly different for the western part and eastern part of China, which are approximately separated by the longitudinal line at 104E. (2) Phase velocity maps at shorter periods (20-35s) are influenced by topography and crustal thickness. On these maps, the western part is characterized by apparent low phase velocity,except Qaidam basin with high phase velocities. Tarim basin, Qinghai-Tibet plateau and its eastern margin-Songpan-Ganzi block, form the most prominent low velocity body in the studied area. A large-scale low velocity anomaly also appears in Western Mongolia. Yangtze block (including Sichuan Basin), south-China block, Songliao basin, Sea of Japan, and eastern Mongolia have apparent high phase velocities. (3) At the intermediate periods (40-75s) the area of low velocity anomaly in the west shrinks gradually as the period increases; the phase velocities beneath Himalayan thrust and Tarim Basin as well as Junggar basin become high, implying that Qinghai-Tibet low velocity area is surrounded by 3 high velocity bodies from south, northwest, and east, which may result in a southeastern migration of the low velocity material of the plateau. Meanwhile, the phase velocity distributions in the eastern part become disintegrated with relatively low velocity bodies beneath the East China Sea and Jilin region. (4) At longer period (80-100s) low velocity anomaly in Qinghai-Tibet plateau becomes weaker and weaker as period increases, and apparent low velocity bodies appear gradually beneath the eastern part of China. Northern Indo-China block and its adjacent sea area, East China Sea, Jilin region, and eastern Mongolia are dominated by prominent low velocity anomalies at the period 120s, which suggests a wide distribution of asthenosphere there. However, high phase velocities appear in Yangtze block (including Sichuan Basin), which may imply the absence of asthenosphere in the upper mantle beneath this relatively stable block. (5) North-South seismic belt in China has relatively low phase velocity from periods 20s to 120s, and becomes a natural boundary dividing the continental China into two parts with different phase velocity feature. In the next step, we will construct empirical Greens functions (EGFs) for pairs of stations from ambient seismic noise by using monthly or yearly data and measure shorter periods (e.g., 10-30s) surface-wave dispersion data from the obtained EGFs. Finally, we will combine phase velocity dispersion data from two-station analysis and EGFs to invert for crust and upper mantle structure in the continental China. Keywords: rayleigh wave, phase velocity distribution, chinese continent

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