HR: 0800h
AN: T51B-0540    [Abstracts]
TI: Body-Wave Attenuation Structure in Central Mexico
AU: Clayton, R W
EM: clay@gps.caltech.edu
AF: Caltech, MC 252-21 1200 E California Blvd, Pasadena, CA 91125, United States
AU: * Chen, T
EM: tchen@gps.caltech.edu
AF: Caltech, MC 252-21 1200 E California Blvd, Pasadena, CA 91125, United States
AB: Velocity spectra from moderate-sized earthquakes are used to investigate the P-wave attenuation structure in southern Mexico. In particular, we include regional events with magnitudes in the range 4.5 < M < 6.1 recorded from February 2005 to March 2007 on the Meso American Subduction Experiment (MASE) array, which consists of 100 broadband sensors from Acapulco to Tampico in central Mexico. By assuming a Brune-type source, a path-averaged frequency-independent Q is obtained for each seismogram in the frequency band 2 to 30 Hz, depending on the signal quality. These measurements are then inverted for spatial variations in Q. The 1- D tomography result shows a pattern of Q qualitatively similar to other subduction zones, with low attenuation crust (Q ~~1100), and high attenuation in the mantle wedge beneath the Trans-Mexico-Volcanic-Belt (Q < 250). The 2-D inversion shows more detail, with a low-Q zone above the slab between the depth of 100 km and 120 km. The location of the low-Q region provides some constraints on the geometry of the subducting slab, or with the structure provided by other methods such as receiver functions, the Q estimates will be used to estimate variations in viscosity. We also find that there are some attenuation variations in the crust.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2007 Fall Meeting