HR: 0830h
AN: S41A-01    [Abstracts]
TI: Crust and Upper Mantle Structure Beneath Sichuan/Yunnan Provinces, SW China: Preliminary Results of a Joint MIT-CIGMR Broad-Band Seismometry Project
AU: * van der Hilst, R
EM: hilst@mit.edu
AF: EAPS-MIT, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Chen, Z
EM: zhilchen@mail.sc.cninfo.net
AF: Chengdu Institute for Geology and Mineral Resources, 82 First Ring Road, Chengdu, SC 610082 China
AU: Li, C
EM: changli@mit.edu
AF: EAPS-MIT, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Lev, E
EM: einatlev@mit.edu
AF: EAPS-MIT, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: xu, l
EM: lilixu@mit.edu
AF: EAPS-MIT, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AU: Yao, H
EM: hjyao@mit.edu
AF: EAPS-MIT, 77 Massachusetts Ave, Cambridge, MA 02139 United States
AB: As part of a multi-year NSF Continental Dynamics project investigating the structure and geological evolution of the eastern part of the Tibetan plateau, we operated a 25 station array (3-component, broad band seismometers) in Sichuan and Yunnan provinces, from 09/2003-09/2004. A prime overall objective of the seismometry project is to establish the level of mechanical coupling between the (upper) crust and the mantle, and specific targets include (1) determination of crustal structure, (2) characterization of (shallow) mantle interfaces beneath SW China, (3) characterization of seismic anisotropy in crust and shallow mantle, and (4) determination of upper mantle structure through travel time and surface wave array tomography. Receiver function analysis has produced maps of Moho depth and evidence for a mid crustal low-velocity zone, which appears to thin eastwards from the high plateau to the lowlands of Yunnan and Sichuan. A two layer anisotropy model suggest a spatially coherent pattern of fast axes of olarization in the upper crust that is consistent with inferences from GPS studies but quite different from the direction of anisotropy at larger depth. This observation is strongly suggestive of mechanical decoupling of crust and mantle. Incorporating the travel times of phases recorded at the array allow us to constrain upper mantle structure with much greater resolution and confidence than before, and the preliminary models reveal intriguing variations in P-wavespeed in the upper mantle beneath the Red River fault zone. For example, some of the seismically slow structures beneath the eastern part of the plateau may connect to structure, and presumably, processes in the upper mantle beneath the South China Sea.
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2005 Joint Assembly