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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 2305
Structure of the crust and upper mantle in the Qinghai-Tibet Plateau and
its adjacent areas
Dr. Xuemei Zhang
Institute of Geology and Geophysics Chinese Academy of Sciences IASPEI
Teng Jiwen
The Qinghai-Tibet Plateau, formed by the successive convergence and the continent-continent between
Indian and Eurasian plates since 50Ma ago, is the key earth science laboratory for the understanding of
the collision and mountain building mechanism. By their interaction the shallow and deep structures are
very complicated. Many geophysicists gained a series of important accomplishment about the deep
structure beneath the Qinghai-Tibet Plateau. However there are few studies on the fine structures of
the lithosphere-asthenosphere system. Our study area is in the range of 18ºN- 42ºN and 70ºE -106ºE.
In this study we collect long period (8s-150s) seismic records during the period of 1987-2003. In most
of the Qinghai-Tibet plateau the horizontal resolution close to 200km. Based on our results of pure
dispersions of Rayleigh wave tomography, taking S wave velocities from our linear inversion as the
initial model, using simulated annealing algorithm, we carry out non-linear simultaneous inversion of the
interface positions and S wave velocity. With the analyses of S wave velocity, we recognized the
character of velocity structures and the thicknesses of the crust and the lithosphere. The results
demonstrate the S wave velocity distribution and the crustal and the lithpspheric thicknesses varying in
different terranes. In the profiles, the Yarlung-Zangbo fault, Bangong-Nujiang fault, Jinshajiang fault
and Altyn Tagh fault are obvious boundaries of velocity anomalies. The crust is rather thick with
relatively lower velocity in the Qinghai-Tibet Plateau, varies from 60km to 80km, whereas the lithosperic
thickness is thinner (130km-160 km) than its adjacent areas. Beneath the Qiantang Terrane where is a
crust-mantle transition zone with no distinct velocity jump and Cenozoic lava with rich kalium element,
the S wave velocity is relatively lower about 4.1-4.4km/s from 150km to 230km. The image of S wave
velocities displays that the north-dipping higher velocity anomaly of the upper mantle is end at the
Bangon-nujiang suture. has a thinner crust (32km-38km) with relatively higher velocity and rather
thicker lithosphere of 190km. Sichuan and Tarim basins have the crust thickness less than 50km and
thicker lithospheres.
Keywords: qinghai tibetplateau, non linearinversion, seismictomography