Pressure solution strain and seismogenesis in an active compressional belt: The San Cayetano fault in the Transverse Ranges of California
Jan Vermilye, & Leonardo SeeberSubmitted 2002, SCEC Contribution #651
Pressure solution strain is a significant component of the total permanent strain in the upper crust. It is geodetically indistinguishable from elastic strain and thus needs to be accounted for in realistic models of tectonics and future seismicity. We examine structures in sedimentary rock near the San Cayetano thrust, a major active fault. We distinguish three components of pressure solution controlled deformation: 1) grain boundary dissolution; 2) shortening across cleavage planes; and 3) aseismic slip on small (gouge-free) faults. Structures from all three mechanisms indicate N-S to NE-SW shortening directions, which are consistent with the current tectonic setting and stress orientations. Measurements of minimum shortening yield 4-21% by grain-boundary dissolution and 1-32% by formation of cleavage planes. These are regional, layer-parallel strains and they accumulated over ~3my of compressional tectonics prior to slip on the San Cayetano fault. Similar ongoing strains in the Los Angeles and Ventura basins could account for as much as 20% of the geodetic strains. In contrast, pressure solution strain by small faults (0.01 to 11%) is concentrated within 2 km of the San Cayetano fault. Changes in rates for pressure solution activity may be coupled with changes in stress and fluid circulation during the earthquake cycle.
Citation
Vermilye, J., & Seeber, L. (2002). Pressure solution strain and seismogenesis in an active compressional belt: The San Cayetano fault in the Transverse Ranges of California. Journal of Structural Geology, (submitted).
