HR: 14:00h
AN: T23G-02 INVITED    [Abstracts]
TI: Constraints on Crust and Upper Mantle Structure Beneath Tibet from Multi-scale, Finite- Frequency Travel-time Tomography
AU: * Hung, S
EM: shung@ntu.edu.tw
AF: National Taiwan University, Department of Geosciences National Taiwan University, Taipei, 106, Taiwan
AB: In order to illuminate the inner-works of continental collision between India and Asia, several studies have used travel-time tomography to image variations in seismic velocities under Tibet. Partly due to very sparse station distributions, global tomography has resolved only very broad features such as seismically slow crust and lithospheric mantle beneath central Tibet and long-wavelength, high-velocity anomalies underneath the southern edge of Tibet which have been attributed to under-thrusting of the Indian lithosphere (e.g., Li et al., 2006). Since 1991, data from arrays of broadband deployments in the interior of the Tibetan Plateau and the Himalayas have provided steady improvements to the resolution of crust and upper mantle structure beneath this key collision zone. From September of 2002 to August of 2005, Project Hi-CLIMB completed an N-S trending linear array of over 800 km in length across the Himalaya-Tibetan collision zone and a complementary, E-W trending regional array in southern Tibet of comparable aperture. Data from over 210 stations, spaced only 3-8 km apart in the linear array, provide for unprecedented spatial resolution in tomography. Using this new dataset, I report results of 3-D, tomographic inversion of P-wave travel-times, including P, PKIKP and PcP phases, as measured by inter-station cross-correlation of waveforms at both high- (0.3-2 Hz) and low-frequencies (0.03-0.125 Hz). In the inversion, I employed physically realistic 3-D sensitivity kernels for travel-time delays and multi-scale parameterization that facilitates spatially-varying, data-adaptive resolutions. The most robust and surprising results include two disjointed anomalies of low-velocity in the lithosphere, confined to depths of about 150 km or less near the Indus-Yarlong suture (IYS). One anomaly is about 100 km in radius, centered around 29.5°N, 86°E just north of the IYS, and the other lies farther eastward and straddles the IYS. The former anomaly clearly correlates with a localized region of gradual crust-mantle transition while the latter seems to coincide with an anomalous zone of null shear-wave birefringence. At greater depths, a broad swath of high P-wave speeds extends under much of the Lhasa terrane beyond the Bangong-Nujiang Suture (BNS), consistent with the notion that the leading edge of the Indian mantle lithosphere (¡§Greater India¡¨) extends just beyond the BNS.
DE: 7203 Body waves
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8108 Continental tectonics: compressional
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting