Modeling of Three-Dimensional Regional Velocity Structure Using Wide-Angle Seismic Data from the Hi-CLIMB Experiment in Tibet
GRIFFIN, J.D., Purdue University, West Lafayette, Indiana, firstname.lastname@example.org; NOWACK, R.L., Purdue University, West Lafayette, Indiana, email@example.com; TSENG, T.L., Tawain National University, Taipei, Taiwan, firstname.lastname@example.org; CHEN, W.P., University of Illinois, Urbana, Illinois,
Using data from local and regional events 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. We construct more than 30 high-quality, regional seismic profiles, and select 8 of these, which show excellent crustal and Pn arrivals, for further analysis. Travel-times from four close-in events provide details on crustal velocities, and four events at regional distances 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. Preliminary estimates of upper mantle velocity gradients are between .003 and .004 km/s per km, consistent with previous results by Phillips et al. (2007). 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.