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The relationship between upper mantle anisotropic structures beneath California, transpression, and absolute plate motions

Kosarian, Minoo and Davis, Paul M. and Tanimoto, Toshiro and Clayton, Robert W. (2011) The relationship between upper mantle anisotropic structures beneath California, transpression, and absolute plate motions. Journal of Geophysical Research B, 116 . Art. No. B08307. ISSN 0148-0227. https://resolver.caltech.edu/CaltechAUTHORS:20110909-102813331

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Abstract

We calculated SKS splitting parameters for the California Integrated Seismic Network. In southern California, we also estimated splitting in the upper 100 km using azimuthal anisotropy determined from surface waves. The inferred splitting from surface waves in the mantle lithosphere is small (on average < 0.2 s) compared with SKS splitting (1.5 s) and obtains a maximum value (0.5 s) in the transpressive region of the Big Bend, south of, and aligned with, the San Andreas Fault (SAF). In contrast, the SKS splitting is approximately E-W and is relatively uniform spatially either side of the Big Bend of the SAF. These differences suggest that most of the SKS splitting is generated much deeper (down to 300–400 km) than previously thought, probably in the asthenosphere. Fast directions align with absolute plate motions (APM) in northern and southeastern California but not in southwestern California. We interpret the parallelism with APM as indicating the SKS anisotropy is caused by cumulative drag of the asthenosphere by the overlying plates. The discrepancy in southwestern California arises from the diffuse boundary there compared to the north, where relative plate motion has concentrated near the SAF system. In southern California the relative motion originated offshore in the Borderlands and gradually transitioned onshore to the SAF system. This has given rise to smaller displacement across the SAF (160–180 km) compared with central and northern California (400–500 km). Thus, in southwestern California the inherited anisotropy, from prior North American APM, has not yet been overprinted by Pacific APM.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1029/2010JB007742DOIArticle
http://www.agu.org/pubs/crossref/2011/2010JB007742.shtmlPublisherArticle
ORCID:
AuthorORCID
Clayton, Robert W.0000-0003-3323-3508
Additional Information:© 2011 American Geophysical Union. Received 3 June 2010; accepted 19 May 2011; published 20 August 2011. This research was supported by the Southern California Earthquake Center. SCEC is funded by NSF cooperative agreement EAR-8920136 and USGS cooperative agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. SCEC contribution 1482. Data were obtained from the Southern and Northern California Data Centers. Dave Okaya is thanked for anisotropy calculations used to test the stripping method. Karen Fischer is thanked for providing the propagator matrix coded for anisotropic layers. Two reviewers provided comments that substantially improved the paper.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
Southern California Earthquake Center (SCEC)UNSPECIFIED
NSFEAR-8920136
USGS14-08-0001-A0899
USGS1434-HQ-97AG01718
Subject Keywords:California; anisotropy; motions; plate; seismic; transpression
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Southern California Earthquake Center (SCEC)1482
Record Number:CaltechAUTHORS:20110909-102813331
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20110909-102813331
Official Citation:Kosarian, M., P. M. Davis, T. Tanimoto, and R. W. Clayton (2011), The relationship between upper mantle anisotropic structures beneath California, transpression, and absolute plate motions, J. Geophys. Res., 116, B08307, doi:10.1029/2010JB007742.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:25269
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Sep 2011 18:24
Last Modified:03 Oct 2019 03:04

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