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Upper Crustal Structure from the Santa Monica Mountains to the Sierra Nevada, Southern California: Tomographic Results from the Los Angeles Regional Seismic Experiment, Phase II (LARSE II)

Lutter, W. J. and Fuis, G. S. and Ryberg, T. and Okaya, D. A. and Clayton, R. W. and Davis, P. M. and Prodehl, C. and Murphy, J. M. and Langenheim, V. E. and Benthien, M. L. and Godfrey, N. J. and Christensen, N. I. and Thygesen, K. and Thurber, C. H. and Simila, G. and Keller, G. R. (2004) Upper Crustal Structure from the Santa Monica Mountains to the Sierra Nevada, Southern California: Tomographic Results from the Los Angeles Regional Seismic Experiment, Phase II (LARSE II). Bulletin of the Seismological Society of America, 94 (2). pp. 619-632. ISSN 0037-1106. doi:10.1785/0120030058.

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In 1999, the U.S. Geological Survey and the Southern California Earthquake Center (SCEC) collected refraction and low-fold reflection data along a 150-km-long corridor extending from the Santa Monica Mountains northward to the Sierra Nevada. This profile was part of the second phase of the Los Angeles Region Seismic Experiment (LARSE II). Chief imaging targets included sedimentary basins beneath the San Fernando and Santa Clarita Valleys and the deep structure of major faults along the transect, including causative faults for the 1971 M 6.7 San Fernando and 1994 M 6.7 Northridge earthquakes, the San Gabriel Fault, and the San Andreas Fault. Tomographic modeling of first arrivals using the methods of Hole (1992) and Lutter et al. (1999) produces velocity models that are similar to each other and are well resolved to depths of 5-7.5 km. These models, together with oil-test well data and independent forward modeling of LARSE II refraction data, suggest that regions of relatively low velocity and high velocity gradient in the San Fernando Valley and the northern Santa Clarita Valley (north of the San Gabriel Fault) correspond to Cenozoic sedimentary basin fill and reach maximum depths along the profile of ∼4.3 km and >3 km, respectively. The Antelope Valley, within the western Mojave Desert, is also underlain by low-velocity, high-gradient sedimentary fill to an interpreted maximum depth of ∼2.4 km. Below depths of ∼2 km, velocities of basement rocks in the Santa Monica Mountains and the central Transverse Ranges vary between 5.5 and 6.0 km/sec, but in the Mojave Desert, basement rocks vary in velocity between 5.25 and 6.25 km/sec. The San Andreas Fault separates differing velocity structures of the central Transverse Ranges and Mojave Desert. A weak low-velocity zone is centered approximately on the north-dipping aftershock zone of the 1971 San Fernando earthquake and possibly along the deep projection of the San Gabriel Fault. Modeling of gravity data, using densities inferred from the velocity model, indicates that different velocity-density relationships hold for both sedimentary and basement rocks as one crosses the San Andreas Fault. The LARSE II velocity model can now be used to improve the SCEC Community Velocity Model, which is used to calculate seismic amplitudes for large scenario earthquakes.

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Clayton, R. W.0000-0003-3323-3508
Additional Information:© 2004 by the Seismological Society of America. Manuscript received 24 March 2003. This research was supported by the U.S. Geological Survey, Department of the Interior (USGS Cooperative Agreement 00HQGR0053 and USGS internal funds), National Science Foundation (NSF Cooperative Agreement EAR-97-25413), Southern California Earthquake Center (SCEC, which is funded by NSF Cooperative Agreements EAR 8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718), Deutsche Forschungsgemeinschaft, and GeoForschungsZentrum Potsdam, Germany. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. government. Instruments were supplied by IRIS/PASSCAL, University of Texas El Paso, Geophysical Instrument Pool Potsdam, Canadian Geological Survey, University of Copenhagen, SCEC, and the USGS. The SCEC Contribution Number for this paper is 677. The facilities of the IRIS Consortium are supported by the National Science Foundation under Cooperative Agreement EAR- 0004370. We are indebted to many government agencies, organizations, companies, and private individuals who granted permission and, in many cases, vital assistance to LARSE II (see table 3 in Fuis et al., 2001a). This manuscript benefited from reviews by Tom Brocher, Andy Michael, and Egill Hauksson.
Group:Seismological Laboratory
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Southern California Earthquake Center (SCEC)UNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
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Southern California Earthquake Center (SCEC)677
Issue or Number:2
Record Number:CaltechAUTHORS:20121001-131459133
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34596
Deposited By: Tony Diaz
Deposited On:01 Oct 2012 20:53
Last Modified:09 Nov 2021 23:09

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