HR: 0830h
AN: S21E-0354    [PDF]
TI: The P-wave Velocity Structure Beneath East Asia
AU: * Li, C
EM: changli@mit.edu
AF: Chang Li, 54-526, Cambridge, MA 02139 United States
AB: Because of poor resolution in the upper mantle, the relationship between the lower mantle structure and recent tectonic processes beneath East Asia is not readily inferred from published P-velocity models. In order to improve the resolution of upper mantle structure beneath East Asia, we combine P-wave travel time data from the Annual Bulletin of Chinese Earthquakes (ABCE) with reprocessed International Seismologic Centre (ISC) data. To the 44 stations in China that report to ISC we thus add data from 105 stations that were previously unavailable. The combined station coverage is substantially denser and more uniform than that used in any previous tomographic study of this region. We recalculate the travel time residuals of ABCE relative to the hypocenter from the catalog by Engdahl et al (1998). We parameterize the upper-mantle structure beneath East Asia with an irregular grid with a grid size that is adapted to sampling density. This allows us to resolve the structure with scale length less than 70 km in regions of dense sampling. We use an a priori 3D crustal model to reduce the artificial mapping of the crustal structure into the upper mantle, which improves the accuracy of the images of upper mantle structure. Our tomographic inversions reveal high-velocity continental roots beneath several continental blocks in East Asia. Beneath the Ordos Plateau and Sichuan Basin the fast seismic velocities continue to at least 200 km depth. These areas are located near a topographic boundary with the Tibetan plateau and Cenozoic crustal thickening has not affected these areas. Beneath the Himalayas a high-velocity anomaly may be associated with the subduction of Indian lithospheric material. This structure is visible near the 410 km discontinuity and seems to be separated from the old sinking ocean slab in the lower mantle. A large-scale high-velocity structure is observed beneath Yangtze Craton in mantle transition zone, which can possibly be explained by the ocean slabs subducted from different directions. In contrast, the low-velocity mantle structure is visible beneath the island of Hainan and south coast of China.
DE: 7218 Lithosphere and upper mantle
DE: 8123 Dynamics, seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting