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Attenuation models (Q_P and Q_S) in three dimensions of the southern California crust: Inferred fluid saturation at seismogenic depths

Hauksson, Egill and Shearer, Peter M. (2006) Attenuation models (Q_P and Q_S) in three dimensions of the southern California crust: Inferred fluid saturation at seismogenic depths. Journal of Geophysical Research B, 111 (B5). Art. No. B05302. ISSN 0148-0227. doi:10.1029/2005JB003947.

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We analyze high dynamic range waveform spectra to determine t* values for both P and S waves from earthquakes in southern California. We invert the t* values for three-dimensional (3-D) frequency-independent Q_P and Q_S regional models of the crust. The models have 15 km horizontal grid spacing and an average vertical grid spacing of 4 km, down to 22 km depth, and extend from the U.S.-Mexico border to the Coast Ranges in the south and Sierra Nevada in the north. In general, QP and QS increase rapidly with depth, consistent with crustal densities and velocities. The 3-D Q_P and Q_S models image the major tectonic structures and to a much lesser extent the thermal structure of the southern California crust. The near-surface low Q_P and Q_S zones coincide with major sedimentary basins such as the San Bernardino, Chino, San Gabriel Valley, Los Angeles, Ventura, and Santa Maria basins and the Salton Trough. In contrast, at shallow depths beneath the Peninsular Ranges, southern Mojave Desert, and southern Sierras, we image high Q_P and Q_S zones, which correspond to the dense and high-velocity rocks of the mountain ranges. Several clear transition zones of rapidly varying Q_P and Q_S coincide with major late Quaternary faults and connect regions of high and low Q_P and Q_S. At midcrustal depths, the Q_P and Q_S exhibit modest variation in slightly higher and lower QP or QS zones, which is consistent with reported crustal reflectivity. In general, for the southern California crust, Q_S/Q_P is greater than 1.0, suggesting partially fluid-saturated crust. A few limited regions of Q_S/Q_P less than 1.0 correspond to areas mostly outside the major sedimentary basins, including areas around the San Jacinto fault, suggesting a larger reduction in the shear modulus compared to the bulk modulus or almost complete fluid saturation.

Item Type:Article
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Hauksson, Egill0000-0002-6834-5051
Shearer, Peter M.0000-0002-2992-7630
Additional Information:© 2006 American Geophysical Union. Received 19 July 2005; revised 17 January 2006; accepted 30 January 2006; published 2 May 2006. The Southern California Seismic Network (SCSN), Kate Hutton, and her staff, processed the data used in this study, and the data are archived at the Southern California Earthquake Data Center. We thank D. Eberhart-Phillips for making the t* code available and C. Thurber for the SIMULPS code. We thank an anonymous and A. Rietbrock reviewers, the Associate Editor, H. Kanamori, J. Boatwright, and L. Jones for reviewing the manuscript. We also thank D. Eberhart-Phillips, H. Kanamori, S. Huusen, and J. Boatwright for stimulating discussions. The figures were done using GMT [Wessel and Smith, 1991]. Supported by NEHRP/USGS grants 04HQGR0052 and 05HQGR0040 and by SCEC, which is funded by NSF Cooperative Agreement EAR-0106924 and USGS Cooperative Agreement 02HQAG0008; SCEC contribution 953. Contribution 9127, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.
Group:Seismological Laboratory
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)UNSPECIFIED
Subject Keywords:attenuation; southern California; crustal fluids; QP; QS
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Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center (SCEC)953
Caltech Division of Geological and Planetary Sciences9127
Issue or Number:B5
Record Number:CaltechAUTHORS:20130514-103125549
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Official Citation:Hauksson, E., and P. M. Shearer (2006), Attenuation models (QP and QS) in three dimensions of the southern California crust: Inferred fluid saturation at seismogenic depths, J. Geophys. Res., 111, B05302, doi:10.1029/2005JB003947.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38488
Deposited On:14 May 2013 22:16
Last Modified:09 Nov 2021 23:37

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