HR: 0800h
AN: T31B-0472    [Abstracts]
TI: Tomographic Imaging of the Crust and Upper Mantle Beneath the Western Tien Shan
AU: * Li, Z
EM: liz2@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180,
AU: Roecker, S
EM: roecks@rpi.edu
AF: Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180,
AB: We combine P and S wave arrival times from the recent MANAS deployment of broad band sensors with the prior GENGHIS deployment and analogue observations from the Kyrgyz Institute of Seismology to generate a high resolution (5-20 km) image of elastic wavespeeds in the crust and upper mantle beneath the western Tien Shan. The total data set consists of 29,006 P and 21,491 S arrivals from 2176 local events along with 27,196 P arrivals from 2631 teleseismic events recorded at 144 stations. Near surface structure is constrained by a combination of arrival times from local and regional events, Moho depths determined from receiver functions, and travel times from the 2007 MANAS active source profile. Our principal finding is a large high wavespeed region in the mantle beneath most of western Tien Shan dipping to the north to depths as great as 600 km. This region appears to be continuous to shallow depths and surfaces at the southern range front near where the Tarim Basin is being overthrust by the Kokshal range. This result suggests that the Tarim Basin continues to actively subduct beneath the Tien Shan. We do not see any similar feature associated with underthrusting of the Kazach shield to the south. We also inverted a subset of regionally located events for Pn wavespeed and anisotropy. Similar to the larger scale results, Pn wavespeeds in the uppermost mantle are 3-4 percent lower than normal under most of the Tien Shan. The fast direction of Pn anisotropy is predominantly north-south in agreement with the sparser sampling of previous SKS studies. Taken with the tomographic image, we suggest that the anisotropy is most likely due to flow in the asthenosphere induced by the subduction of the Tarim basin.
DE: 1038 Mantle processes (3621)
DE: 7218 Lithosphere (1236)
DE: 8107 Continental neotectonics (8002)
DE: 8108 Continental tectonics: compressional
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting