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 across 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 modeling. 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 occurring in Central Asia. ¿ American Geophysical Union 1995