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Lateral velocity variations in Southern California. II. Results for the lower crust from Pn waves

Hearn, Thomas M. and Clayton, Robert W. (1986) Lateral velocity variations in Southern California. II. Results for the lower crust from Pn waves. Bulletin of the Seismological Society of America, 76 (2). pp. 511-520. ISSN 0037-1106.

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A tomographic inversion of the Pn arrivals in Southern California yields new information about wave velocities and topography on the Moho discontinuity. We produce maps of Pn velocity and Pn station delays. The Pn velocities do not show the dramatic correlation with surface faults that is found for the shallower Pg arrivals (Hearn and Clayton, 1986). This implies that the lower crust and mantle are largely decoupled from the upper crust. Undoubtedly, this is due to the different responses of the brittle upper crust and the ductile lower crust to tectonic and isostatic stresses. Detachment faults must play an important role in separating the crust. In general, velocities on the American plate are higher than on the Pacific plate, but no distinct transition is observed. The Colorado River region has extremely thin crust due to basin-and-range type extension. The Transverse Ranges have a small root as seen in the station delays and which also results in slightly lower Pn velocities there. The Peninsula Ranges also have slow Pn velocities, but they do not have late station delays. Any root to the Peninsula Ranges must be very narrow. Isostatic balance must be maintained primarily through lateral density contrasts.

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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 Laboratory4196
Issue or Number:2
Record Number:CaltechAUTHORS:20121017-092616257
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Official Citation:Thomas M. Hearn and Robert W. Clayton Lateral velocity variations in Southern California. II. Results for the lower crust from Pn waves Bulletin of the Seismological Society of America, April 1986, v. 76, p. 511-520
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34944
Deposited By: Ruth Sustaita
Deposited On:17 Oct 2012 16:37
Last Modified:03 Oct 2019 04:23

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