A geodetic study of crustal deformation in the Ventura Basin region, Southern California

Citation

Donnellan, Andrea (1992) A geodetic study of crustal deformation in the Ventura Basin region, Southern California. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ejva-6672. https://resolver.caltech.edu/CaltechTHESIS:09282011-105846249

Abstract

The Ventura basin lies within the north-south compressive western Transverse Ranges in southern California. The basin is characterized by rapid north-south convergence on geologic time-scales, with Quaternary rates of convergence across the basin estimated to be approximately 20 mm/yr. Global Positioning System (GPS) observations carried out over a period of 2.7 years suggest rapid rates of convergence of 7 ± 2 mm/yr on geodetic time scales. The deformation corresponds to a maximum shear strain rate of 0.6 ± 0.1 μrad/yr with the azimuth of maximum compression oriented 16° ± 8° W. The dilatation rate of 0.3 ± .1 x 10^(-6)yr^(-1) indicates that a significant amount of compression is occurring. The strain rates of 0.1 ± 0.1 μrad/yr south of the basin are much lower. Strain rates calculated from the GPS measurements are consistent with those calculated from comparisons between GPS and historical triangulation data. The deformation in the basin region cannot be modeled as a megashear zone, which best describes much of California.

The observed deformation can be modeled by creep on detachment faults both north and south of the basin. Faults near the surface are most likely locked. Rupture of the San Cayetano fault within the next 200 years is possible, resulting in an earthquake of moment magnitude 6.0-6.8. Based on the fault models, the south side of the basin is capable of producing a magnitude 5.5-6.0 earthquake. The models of the short-term deformation suggest that the observed rate is consistent with the geologic record, but that the observations have taken place over a small fraction of the earthquake cycle.

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