HR: 15:10h
AN: S32C-07    [PDF]
TI: The anisotropic seismic structure of the upper mantle beneath Mexico
AU: * Matzel, E
EM: matzel1@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave L-206, Livermore, Ca 94551 United States
AB: We present models for the P and S velocity structure of the upper mantle beneath Mexico, including measurements of radial anisotropy. The data are 3-component broadband seismograms from sources located in southern Mexico and Guatemala recorded at seismic stations located in the southwestern United States. From this we obtained a series of densely sampled SE-NW trending paths covering the major tectonic features of Mexico. Waveform data were inverted to obtain 1D models for each of these paths. The mantle beneath Mexico is characterized by a radially anisotropic seismic lid, which thickens from west to east, overlying a low velocity zone. Most of the variation between profiles occurs in the top 200 km, generally related to subduction. S anisotropy is high in the lid (6-8%), but the mantle is largely isotropic below that. P anisotropy is not well resolved, but P structure mimics the SH velocity structure, suggesting that P is also anisotropic within the lid. The VP/VSH ratio (1.86) is nearly constant as a function of depth from the Moho through the transition zone.
DE: 3210 Modeling
DE: 7207 Core and mantle
DE: 7218 Lithosphere and upper mantle
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting