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Lateral velocity variations in southern California. I. Results for the upper crust from Pg waves

Hearn, Thomas M. and Clayton, Robert W. (1986) Lateral velocity variations in southern California. I. Results for the upper crust from Pg waves. Bulletin of the Seismological Society of America, 76 (2). pp. 495-509. ISSN 0037-1106.

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The plate boundary and major crustal blocks in southern California are imaged by a tomographic backprojection of the Pg first arrivals recorded by the Southern California Array. The method, formulated specifically for local earthquake arrival times, is a fast, iterative alternative to direct least-squares techniques. With it, we solve the combined problem of determining refractor velocity perturbations and source and station delays. Resolution and variance are found empirically by using synthetic examples. A map showing lateral velocity variations at a depth of approximately 10 km is presented. The results show a strong correlation with surface tectonic features. Clear velocity contrasts exist across the San Andreas, the San Jacinto, and the Garlock faults. The Mojave region has the slowest velocities while the Peninsula Ranges have the highest. The San Jacinto block has velocities intermediate between Mojave and Peninsula Range velocities, and also has early station delays. This may indicate that the San Jacinto block has overridden Mojave material on a shallow detachment surface. No velocity variations are found associated with the Transverse Ranges, which we interpret to mean that the surface batholithic rocks in this area do not extend to Pg depths.

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Clayton, Robert W.0000-0003-3323-3508
Additional Information:© 1986 by the Seismological Society of America. Manuscript received 6 August 1985. This study was supported by a research contract with the U.S. Geological Survey (14-08-001-21210) and a grant from the Sun Oil Company. Part of the graphics and computing facilities used in this study were provided by the W. M. Keck Foundation. We thank Eugene Humphreys, Leon Silver, and Hiroo Kanamori for their suggestions and reviews.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
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Caltech Seismological Laboratory 4195
Issue or Number:2
Record Number:CaltechAUTHORS:20121017-082856409
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Official Citation:Thomas M. Hearn and Robert W. Clayton Lateral velocity variations in southern California. I. Results for the upper crust from Pg waves Bulletin of the Seismological Society of America, April 1986, v. 76, p. 495-509
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34942
Deposited By: Ruth Sustaita
Deposited On:17 Oct 2012 16:30
Last Modified:03 Oct 2019 04:23

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