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Ever since the recognition of plate tectonics as a major Earth process, maps of the orientation of stress in Earth's crust have given us one of the most direct clues to the forces that drive plate movements. We now know from these maps that stress orientations are consistent on a regional scale, that the boundaries between provinces of uniform stress direction generally coincide with major physiographic and structural boundaries, and that for many regions the orientation of the maximum compressive horizontal stress generally coincides with directions of plate motion [e.g., Zoback and Zoback, 1989].

On a regional scale, maps of crustal stress have provided striking evidence of the low strength of plate margin at the San Andreas Fault in California [M. D. Zoback et al, 1988]. In industry, maps of stress orientations have been used to plan secondary recovery projects for oil and gas [Bell and Babcock, 1986] and evaluate seismic risk near critical facilities [e.g., Stock et al., 1985].