GPS Study of the Kinematics of the Intersection of the Tarim, Tien Shan, and Pamir

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High quality results from a dense GPS network spanning the Central Tien Shan, fromKazakhstan, through Kyrgyzstan, and into China, reveal a relatively simple kinematic picture to the east of the Talas-Ferghana fault. GPS velocities from several independent studies agree that there is ~20 mm/yr convergence between the Tarim Basin and the Kazakh platform, about half the total convergence between the Indian and Eurasian plates. GPS velocities from the PI's dense network show that convergence is localized on a handful of structures. Slip rates on these structures inferred from both geologic studies and geodetic studies agree remarkably well. The PI's have used this new geodetic data, in conjunction with a simple block model that accounts for elastic strain accumulation, to invert for the motions of crustal blocks in the region. Notable results include much less right-lateral motion on the Talas-Ferghana fault than the previous geological estimate, rotation of the Ferghana Valley at ~0.8 degree/myr (a fraction of the long-term geologic rate from paleomag), and convergence across the Alay valley between the Pamir and Southern Tien Shan of ~20 mm/yr, comparable to previous estimates. However, existing geodetic coverage in the west, across the Talas-Ferghana fault into the Ferghana basin, and south across the Alay valley and South Tien Shan and into the Pamir, is both more sparse and less accurate than that in the Central Tien Shan. These rates of strike-slip motion on the Talas Ferghana fault, rotation of the Ferghana basin,and convergence across the Alay valley are not well constrained. For example, the inferred rate of rotation of the Ferghana basin differs by a factor of two depending upon which GPS results are used to constrain the model. Clearly, more observations are needed to obtain results in this area comparable in usefulness to those obtained to the east. In addition, the proposed joint analysis of the PI's raw GPS data with that taken by others (GFZ and CSB) will provide a combined solution with improved accuracy. In collaboration with colleagues at the Russian Institute for High Temperature Physics (known as IVTRAN)in Kyrgyzstan, the PI's propose to install 20 new sites in western Kyrgyzstan and Uzbekistan. The Chinese Seismological Bureau (CSB)in Wuhan, China, will work with us to install additional sites in northwestern Xinjiang Province in China (exact number and locations to be determined after a visit to the field). The PI's collaborators will survey these sites, as well as existing sites that GFZ, IVTRAN, and CSB previously installed in the region, in order to unravel the kinematics of the area where the Tien Shan, Ferghana Basin, Pamir, and Tarim Basin intersect. In addition to analyzing the GPS data, they will also use simple continuum mechanics-based models to interpret the GPS velocities that they obtain in terms of geologic motions.