HR: 11:10h
AN: T52A-04 [Abstracts]
TI: Seismic Anisotropy in Eastern Tibet From Shear-Wave Splitting - Evidence for Crust-Mantle
De-coupling
AU: * Lev, E
EM: einatlev@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77
Massachuestts Ave, Cambridge, MA 02139
United States
AU: Long, M D
EM: mlong@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77
Massachuestts Ave, Cambridge, MA 02139
United States
AU: van der Hilst, R D
EM: hilst@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77
Massachuestts Ave, Cambridge, MA 02139
United States
AB:
Shear wave splitting measurements were obtained for core-refracted waves recorded at 25 broadband stations deployed by MIT in
eastern Tibet in 2003. Two analysis methods were used - the multichannel method, developed by Chevrot, and the
single-channel cross-correlation method, described by Levin, Menke, Park and others. Models assuming a single layer of
anisotropy could not explain a large portion of the observations, and a model incorporating two anisotropic layers was found
to improve the fit to the data significantly for the majority of the stations. The fast directions of shear-wave polarization
for the two layers were different, revealing a fundamental difference in their deformation history and mechanism. Fast
directions in the lower, thicker layer show broader regional coherency, revealing a deeper source. Fresnel zone
considerations constrain the depth of the lower layer to be less than 160 km. In the presumably thinner upper layer the
calculated fast polarization directions align with shear directions along major strike-slip faults in the area, and can be
interpreted to represent the crustal strain field. The discrepancy between the inferred crustal and upper mantle deformation
strongly supports a model where the upper crust is mechanically decoupled from the mantle, possibly by a weak lower crust.
DE: 1209 Tectonic deformation (6924)
DE: 1236 Rheology of the lithosphere and mantle (7218, 8160)
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
SC: Tectonophysics [T]
MN: Fall Meeting 2005