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Lower crustal deformation beneath the central Transverse Ranges, southern California: Results from the Los Angeles Region Seismic Experiment

January 1, 2002

We present a P wave velocity model derived from active source seismic data collected during the 1994 Los Angeles Region Seismic Experiment. Our model extends previously published upper crustal velocity models to mantle depths. Our model was developed by both ray tracing through a layered model and calculating travel times through a gridded model. It includes an 8-km-thick crustal root centered beneath the surface trace of the San Andreas fault, north of the highest topography in the San Gabriel Mountains. A simple mass balance calculation suggests that ∼36 km of north-south shortening across the San Andreas fault in the central Transverse Ranges could have formed this root. If north-south compression began when the “Big Bend” in the San Andreas fault formed at ∼5 Ma, 36 km of shortening implies a north-south contraction rate of ∼7.1 mm/yr across the central Transverse Ranges. If, instead, north-south compression began when the Transverse Ranges formed at 3.4–3.9 Ma, 36 km of shortening implies a contraction rate of 9.2–10.6 mm/yr. North of the San Andreas fault, the Mojave Desert crust has a low-velocity (6.3 km/s) mid and lower crust and a 28-km-deep Moho. South of the San Andreas fault, beneath the Los Angeles and San Gabriel Valley basins, there is a fast (6.6–6.8 km/s), thick (10–12 km) lower crust with a 27-km-deep Moho. Farther south still, the lower crust of the Continental Borderland is fast (6.6–6.8 km/s) and thin (5 km) with a shallow (22 km deep) Moho.

Citation Information

Publication Year 2002
Title Lower crustal deformation beneath the central Transverse Ranges, southern California: Results from the Los Angeles Region Seismic Experiment
DOI 10.1029/2001JB000354
Authors N. J. Godfrey, Gary S. Fuis, Victoria E. Langenheim, David A. Okaya, Thomas M. Brocher
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research B: Solid Earth
Index ID 70024580
Record Source USGS Publications Warehouse
USGS Organization Earthquake Science Center; Geology, Minerals, Energy, and Geophysics Science Center