HR: 0800h
AN: G21A-0105    [Abstracts]
TI: Crustal Deformation in Jiashi Region,China Inferred from GPS
AU: * Meng, G
EM: mengguojie@sina.com
AF: Institue of Earth Sciences, Fuxing Avenue 63, Beijing, 100036 China
AU: Shen, X
EM: shenxh@seis.ac.cn
AF: Institue of Earth Sciences, Fuxing Avenue 63, Beijing, 100036 China
AU: Zhang, Q
EM: qwzhang\_hust@163.ocm
AF: Huazhong University of Science and Technology, Luoyu Road 14, Wuhan, 430074 China
AU: Qiao, X
EM: whgps@public.wh.hb.cn
AF: Institute of Seismology, Xiao Hong Shan 70, Wuhan, 430071 China
AB: The Jiashi region lies in the north of collision zone between the Indian and Eurasian plates and it is a complex region with distributed seismicity and many active faults. A dozens of moderate and strong earthquakes have occurred there since 1900. Seven events greater than M6 took place consecutively during 3 months in 1997. In order to monitor crustal deformation, we started GPS observations in this region since 1994. A total of 9 stations, which are part of GPS moitoring network in southern Tienshan, were constructed within the area about 800 km long and 640 km wide. All of these stations were observed in campaign mode at least 2 times in 1994-2000. In each survey, 4-5 dual-frequency geodetic GPS receivers were utilized to collect the data at different stations simultaneously. All the stations were observed for 3 to 7 consecutive days with continuous recording for almost 24 hours a day. Data from three continuous IGS stations (SELE, POL2, KIT3) are also included in this study. All GPS data acquired either from campaign mode or continuous observations were processed with GAMIT/GLOBK software packages. Firstly we used the GAMIT software to get daily solutions with loose constraints to regional stations and tight constraint to the three IGS stations. Then the daily solutions are utilized to estimate the velocities of GPS stations. In this study we adopt ITRF97 reference frame. We also estimate strain field from the velocity of all GPS stations in this region. GPS monitoring in the Jiashi region provides us with a description of present-day curstual deformation. The main conclusions of this study are summarized as the following: All stations, as a whole in the Jiashi region move northward in the nearly north-south direction relative to northern Tianshan. Tarim basin push Tianshan in the direction perpendicular to Tianshan range. We estimate that the northward motion of GPS stations between $39.5\deg$N and $41.5\deg$N decreases from west to east, with the rate approximating 1.0mm/yr per degree. The GPS stations in the northwest of Kashi and Wushi move in different direction from those stations in the southeast, implying that a counter-clockwise rotation exists along the stations Kashi and Wushi, consitent with geological investigation. Given the current spacing of GPS stations, we cannot find that there are significant deformation apparently concentrating on any local area or active faulting. The strain estimation demonstrates that the principal axis is nearly in north-south direction. Compressure force dominates this region,which are consistent with the results inferred from the analysis of initial p phase of the events greater than M5 in the soutern Tienshan region during 1968-1982, which showed that compressure axis in Pamir and Karokunlun-west Tianshen was mostly in N-S direction, with plunge angle being horizontal. Our result demonstrates that there exists strong compressure in the directions of N-S and NNE-SSW. This might imply that northward movement of India plate is the main source of pushing force and the crustal deformation regime in the Jiashi region is related to the ongoing northward movement of India plate.
DE: 8150 Plate boundary--general (3040)
DE: 1709 Geodesy
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting