Crustal structure of the Borderland-Continent Transition Zone of southern California adjacent to Los Angeles
Article first published online: 30 AUG 2003
Copyright 2003 by the American Geophysical Union.
Journal of Geophysical Research: Solid Earth (1978–2012)
Volume 108, Issue B8, August 2003
How to Cite
2003), Crustal structure of the Borderland-Continent Transition Zone of southern California adjacent to Los Angeles, J. Geophys. Res., 108, 2404, doi:10.1029/2001JB000223, B8., and (
- Issue published online: 30 AUG 2003
- Article first published online: 30 AUG 2003
- Manuscript Accepted: 11 FEB 2003
- Manuscript Revised: 16 MAY 2002
- Manuscript Received: 31 JUL 2000
- California Borderland;
- transition zone;
 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.