HR: 0830h
AN: T11D-0422    [PDF]
TI: Tectonic implications of the thermal regime, San Francisco Bay Area, California
AU: * Harris, R N
EM: rnharris@mines.utah.edu
AF: University of Utah, Department of Geology and Geophysics, 135 South 1460 East, Salt Lake City, UT 84112 United States
AU: Williams, C F
EM: colin@usgs.gov
AF: U.S. Geological Survey, MS 977, 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: An integral element to understanding rheology, continental deformation, evolution and geodynamics is knowledge of the subsurface thermal regime. Five boreholes, recently drilled for strain meter emplacement along the San Andreas Fault System (SAFS) in the San Francisco Bay Area, California provided an opportunity to collect new heat flow values within this dynamic area. These new values fill gaps in existing heat flow coverage in the central and northern Bay Area, and help constrain the role of temperature in determining the spatial and temporal pattern of deformation within this plate boundary zone. The five boreholes vary in depth from 140 to 220 meters and penetrate Cretaceous and Jurassic age sedimentary, metamorphic and igneous rocks of the Franciscan and Salinian blocks. Temperature profiles were recorded in each borehole, and more than 200 thermal conductivities were measured on drill cuttings and core samples. Reliable heat flow values were acquired at four of the five sites and range from approximately 78 to 92 mW m$^{-2}$. The average heat flow from these four sites together with 12 previously published values from the San Francisco Bay Area west of the Calaveras fault is 87 mW m$^{-2}$ with a standard deviation of 8 mW m$^{-2}$. Overall, the new data within the SAFS are consistent with elevated heat flow that characterizes the California Coast Ranges and confirm the continuation of this thermal regime along both the northern segment of the Hayward fault and the section of the San Andreas fault offshore San Francisco. Locally, variations in heat flow along the SAFS may reconcile along strike discrepancies between observed surface slip after the 1906 San Francisco earthquake and geodetic models for coseismic slip, through the influence of thermal conditions on the maximum depth of seismic moment release.
DE: 8130 Heat generation and transport
DE: 8150 Plate boundary--general (3040)
DE: 8159 Rheology--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting