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Crustal Structure in Southern California from Array Data


Hearn, Thomas Martin (1985) Crustal Structure in Southern California from Array Data. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/B6HA-4P68.


Crustal structure in Southern California is investigated using travel times from over 200 stations and thousands of local earthquakes. The data are divided into two sets of first arrivals representing a two-layer crust. The Pg arrivals have paths that refract at depths near 10 km and the Pn arrivals refract along the Moho discontinuity. These data are used to find lateral and azimuthal refractor velocity variations and to determine refractor topography.

In Chapter 2 the Pn raypaths are modeled using linear inverse theory. This enables statistical verification that static delays, lateral slowness variations and anisotropy are all significant parameters. However, because of the inherent size limitations of inverse theory, the full array data set could not be processed and the possible resolution was limited. The tomographic backprojection algorithm developed for Chapters 3 and 4 avoids these size problems. This algorithm allows us to process the data sequentially and to iteratively refine the solution. The variance and resolution for tomography are determined empirically using synthetic structures.

The Pg results spectacularly image the San Andreas Fault, the Garlock Fault and the San Jacinto Fault. The Mojave has slower velocities near 6.0 km/s while the Peninsular Ranges have higher velocities of over 6.5 km/s. The San Jacinto block has velocities only slightly above the Mojave velocities. It may have overthrust Mojave rocks. Surprisingly, the Transverse Ranges are not apparent at Pg depths. The batholiths in these mountains are possibly only surficial.

Pn velocities are fast in the Mojave, slow in Southern California Peninsular Ranges and slow north of the Garlock Fault. Pn anisotropy of 2% with a NWW fast direction exists in Southern California. A region of thin crust (22 km) centers around the Colorado River where the crust bas undergone basin and range type extension. Station delays see the Ventura and Los Angeles Basins but not the Salton Trough, where high velocity rocks underlie the sediments. The Transverse Ranges have a root in their eastern half but not in their western half. The Southern Coast Ranges also have a thickened crust but the Peninsular Ranges have no major root.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Geophysics; crustal structure; tomography
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Harkrider, David G.
Thesis Committee:
  • Harkrider, David G. (chair)
  • Clayton, Robert W.
  • Hager, Bradford H.
  • Kanamori, Hiroo
  • Silver, Leon T.
Defense Date:2 November 1984
Non-Caltech Author Email:thearn (AT)
Funding AgencyGrant Number
United States Geological Survey (USGS)14-08-001-21210
Record Number:CaltechTHESIS:10092013-134453343
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7982
Deposited By: Tony Diaz
Deposited On:11 Oct 2013 15:43
Last Modified:21 Dec 2019 03:01

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