Geodetic measurement of deformation in southern California

Citation

Larsen, Shawn Christian (1991) Geodetic measurement of deformation in southern California. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/SPH1-EV56. https://resolver.caltech.edu/CaltechETD:etd-03102008-095117

Abstract

The Global Positioning System (GPS) has rapidly become one of the most important geodetic tools for studying tectonic deformation. With potential 3-dimensional relative positioning accuracies better than 1 cm, GPS can monitor secular deformation as well as rapid strain fluctuations due to seismic and volcanic activity. A 1970/1971 trilateration survey and 1987/1988 GPS observations suggest uniaxial convergence of 6.4 mm/yr oriented N25.1 °E in the eastern third of the Santa Barbara channel, and a combination of convergence and left-lateral shear to the west. GPS surveys have been conducted in the Imperial Valley during 1986, 1988, 1989, and 1990. About 5 ± 1 cm/yr plate-boundary displacement is observed across the valley, somewhat larger than rates obtained through conventional geodesy. These GPS observations have been influenced by the 1987 Superstition Hills earthquake sequence, the first occurrence of a large earthquake within a preexisting GPS network. The measurements suggest 130 cm right-lateral slip along the northwest trending Superstition Hills fault, and 30 cm left-lateral slip along the conjugate northeast trending Elmore Ranch fault. Imperial Valley leveling surveys conducted in 1931, 1941, 1974, 1978, and 1980, are integrated with seismic, geomorphic, and sub-surfacial structural data, to suggest the northern segment of the Imperial fault formed within the last 80,000 years, and support the hypothesis that the Gulf of California rift system is propagating northwestward into the North American continent.

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