| Using data from local and regional earthquakes recorded by the Hi-CLIMB array in Tibet, we utilize P-wave arrival times to constrain a three-dimensional velocity structure in the crust and the upper mantle in western China. Of more than 30 high-quality, regional seismic profiles that have been assembled, we have selected 12 which show excellent crustal and Pn arrivals, for further analysis. Travel-times from four nearby events to the Hi-CLIMB array provide details on crustal velocities, and eight events at regional distances to the array provide further constraint on Moho structure and mantle lid velocities. We use the 3-D ray tracer, CRT, to model the travel-times. Initial results indicate that the Moho beneath the Lhasa terrane of southern Tibet is over 73 km deep with a high Pn speed of about 8.2 km/s. In contrast, the Qiangtang terrane farther north shows a thinner crust, by up to 10 km, and a low Pn speed of 7.8-7.9 km/s. Travel-times from events to the west and east of the array indicate that both Moho structure and mantle-lid velocities in the region are highly three-dimensional and share a general trend with surface topography. |
