We inverted over one thousand P arrival times from regional distances, in and around the Tibetan Plateau to map the lateral velocity variation within the uppermost mantle. We improve resolution by using forty events recorded at stations within the Tibetan Plateau. We combine these data with observations obtained from the International Seismological Centre to extend our coverage by including Pn arrivals from eightyfive additional plateau events, relocated in previous studies, and recorded at stations in and around the Tibetan Plateau. We use synthetic travel time data to evaluate the resolution of our data set. The observations provide good resolution to about one degree over most of the plateau and surrounding regions. Our results show average Pn velocities that are about three percent lower in the northern plateau relative to the southern plateau. These variations correlate well with major tectonic features and previous geophysical observations. In the Qiangtang terrane of the northern plateau, an area known to be inefficient for Sn propagation, Pn is slow relative to both the plateau south of the Banggong-temperature, velocity, and attenuation are applied, a relatively small temperature variation, is required to explain our Pn velocity observations. When combined with geochemical constraints from volcanics in the northern plateau, our results strongly suggest that the mantle lid is intact beneath the northern plateau. This result would preclude tectonic models involving wholesale delamination of the mantle lithosphere in the northern Tibetan Plateau.
AGU Index Terms: 7200 Seismology; 7203 Body wave propagation; 7205 Continental crust
Keywords/Free Terms: Tibetan Plateau, Pn tomography
JGR-Solid Earth 96JB02112
Vol. 102
, No. B1
, p. 493