Compositional Characterization of Phase 3 Core from the San Andreas Fault Observatory at Depth (SAFOD), Near Parkfield, CA Using Integrated Geological and Geophysical Techniques: Implications for Near Fault Zone Deformation at Seismogenic Depths

Kelly Keighley Bradbury
Utah State University Geology Department Logan, UT; [email protected]

Geological and geophysical characterization of cuttings, core and geophysical logs from 3 - 4 km depth in the San Andreas Fault Observatory at Depth (SAFOD) borehole, provide a unique opportunity to constrain the physical, geochemical, and structural variations within rocks found along an actively creeping section of the San Andreas fault zone, near Parkfield, Ca. This information provides insight into questions related to strength and seismic activity of the fault zone in this area.

This study focuses on the spatial variability of rock properties from surface to depth and integrates geologic and geophysical data sets at the meter to sub-meter scale to further develop a more comprehensive geologic model for this section of the San Andreas Fault. To characterize the relationship between the two data sets, mesoscale core observations along with detailed petrographic, microstructural and X-ray diffraction analyses are compared to geophysical properties such as velocity, gamma ray, density, resistivity, and Possion’s ratio. Ongoing research is aimed at conducting additional analyses of Phase 3 core samples and outcrop-scale field observations and sampling of exhumed fault exposures within similar stratigraphic and structural settings in central to northern California. Review of geologic and geophysical data from available analog cores will be utilized to provide context for the depositional and deformational environment present within Phase 3 core at SAFOD.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid