Chen, Ting and Clayton, Robert W. (2009) Seismic attenuation structure in central Mexico: Image of a focused high-attenuation zone in the mantle wedge. Journal of Geophysical Research B, 114 . Art. No. B07304. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20091110-133506410
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Velocity spectra from moderate-sized earthquakes were used to investigate the P wave attenuation structure in central Mexico. In particular, we included regional events with magnitudes in the range of 4.5 to 6.1 recorded from 2005 to 2007 on the Middle American Subduction Experiment (MASE) array, which consists of 100 broadband sensors across central Mexico from Acapulco to Tempoal, near the Gulf of Mexico. By assuming a Brune-type source, a frequency-independent t* value was obtained for each seismogram in the frequency band 1 to 30 Hz. These measurements were then inverted for two-dimensional spatial variations in Q_p in the cross section along the MASE array, perpendicular to the trench. The model has uniform 20 km vertical grid spacing down to a depth of 200 km and 50 km or 100 km horizontal grid spacing depending on ray coverage. The inversion results show low attenuation in the subducting slab and high attenuation in the mantle wedge and the crust below and to the north of the volcanic belt. The focused high-attenuation zone (Q_p < 200) in the mantle wedge lies away from the top of the slab, between depths of 80 km and 120 km beneath the volcanic belt, and is likely to be related to relatively high temperature, fluids, and partial melts produced in subduction process. The high-attenuation region in the lower crust correlates with the low-resistivity and low-velocity region and could be caused by partial melts and fluids from dehydration and magmatic processes.
|Additional Information:||© 2009 American Geophysical Union. Received 29 July 2008; revised 19 February 2009; accepted 21 April 2009; published 14 July 2009. This study was supported by the Gordon and Betty Moore Foundation through the Tectonics Observatory at Caltech and NSF grant EAR0609707. Contribution 91 from the Caltech Tectonics Observatory. The ray tracing was done using the package developed by William Menke. We thank Donna Eberhart-Phillips for the t* code. We thank two anonymous reviewers for their constructive comments that helped to improve the manuscript.|
|Group:||Caltech Tectonics Observatory, Caltech Tectonics Observatory. MesoAmerican Subduction Experiment (MASE)|
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|Official Citation:||Chen, T., and R. W. Clayton (2009), Seismic attenuation structure in central Mexico: Image of a focused high-attenuation zone in the mantle wedge, J. Geophys. Res., 114, B07304, doi:10.1029/2008JB005964.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||16 Nov 2009 22:13|
|Last Modified:||26 Dec 2012 11:32|
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