ANISOTROPY AND CRUSTAL THICKNESS OF NORTHERN-TIBET - NEW CONSTRAINTS FOR TECTONIC MODELING

In 1993 a seismological array was installed on a profile along the Golmud-Lhasa highway from the Qaidam basin to Central Tibet. A travel time analysis for local and regional earthquakes was performed in order to better constrain the crustal structure obtained by teleseismic tomography. More information about the crustal thickness and anisotropy comes from the analysis of Moho converted P to SV waves. The two methods supplement each other and confirm the existence of crust thinner than expected accross the northern edge of the Tibetan plateau and Qaidam. P to Sv splitting analysis yields a striking similarity between the fast polarization direction and the velocity field of present-day deformation as inferred from kinematic modelling. The two observations, the thinning of the crust and the clockwise rotation of the fast polarization direction emphasize the leading role of eastward extrusion for the absorption of the large amount of crustal shortening occuring in Central Asia.