Nazareth, Julie J. and Clayton, Robert W.
Crustal structure of the Borderland-Continent Transition Zone of southern California adjacent to Los Angeles.
Journal of Geophysical Research B, 108
Art. No. 2404 .
- Published Version
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We use data from the onshore-offshore component of Los Angeles Region Seismic Experiment (LARSE) to model the broad-scale features of the midcrust to upper mantle beneath a north-south transect that spans the continental borderland in the Los Angeles, California, region. We have developed an analysis method for wide-angle seismic data that consists primarily of refractions, lacks near-offset recordings, and contains wide gaps in coverage. Although the data restrict the analysis to the modeling of broad-scale structure, the technique allows one to explore the limits of the data and determine the resolving power of the data set. The resulting composite velocity model constrains the crustal thickness and location and width of the continent-Borderland transition zone. We find that the mid to lower crust layer velocities of the Inner Borderland are slightly lower than the corresponding layers in the average southern California crust model, while the upper mantle velocity is significantly higher. The data require the Moho to deepen significantly to the north. We constrain the transition zone to initiate between the offshore slope and the southwest Los Angeles Basin. If the Inner Borderland crust is 22 km thick, then the transition zone is constrained to initiate within a 2 km wide region beneath the southwest Los Angeles Basin, and have a width of 20–25 km. The strong, coherent, and continuous Pn phase suggests the Moho is coherent and laterally continuous beneath the Inner Borderland and transition zone. The Inner California Borderland seems to be modified and thickened oceanic crust, with the oceanic upper mantle intact beneath it.
|Additional Information:||© 2003 by the American Geophysical Union. Received 31 July 2000; revised 16 May 2002; accepted 11 February 2003; published 30 August 2003. We are grateful to Jeanne Hardebeck, Egill Hauksson, and Patricia Persaud for their reviews of an earlier version of this manuscript. Reviews by Robert Hawman, David Okaya, an anonymous reviewer, and the Associate Editor led to a greatly improved manuscript. We thank Collin Zelt for the use of his program XTRAMP. The map was created with GMT software [Wessel and Smith, 1991]. This work was supported by the Southern California Earthquake Center, which was funded
by NSF Cooperative Agreement EAR-8920136 and USGS Cooperative Agreements 14-08-0001-A0899 and 1434-HQ-97AG01718. SCEC contribution 445. Contribution 8925, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.|
|Funding Agency||Grant Number|
|Southern California Earthquake Center (SCEC)||UNSPECIFIED|
|Subject Keywords:||California Borderland, LARSE, transition zone, slab|
|Other Numbering System:|
|Other Numbering System Name||Other Numbering System ID|
|Southern California Earthquake Center (SCEC)||445|
|Caltech Division of Geological and Planetary Sciences||8925|
|Official Citation:||Nazareth, J. J., and R. W. Clayton, Crustal structure of the Borderland-Continent Transition Zone of southern California
adjacent to Los Angeles, J. Geophys. Res., 108(B8), 2404, doi:10.1029/2001JB000223, 2003|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited On:||01 Oct 2012 18:51|
|Last Modified:||31 Jan 2017 21:13|
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