Collaborative Research: New Heat Flow Values at PBO Borehole Strain Meter Sites: Implications for Deformation

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The overarching goal of EarthScope is to elucidate the dynamics and evolution of the NorthAmerican continent. To reach this goal, focused studies of the continental seismic structure, thestrength of the lithosphere and modes of deformation, the patterns of stresses and strain and themanner in which the lithosphere responds to excitation during earthquakes are all a high priority.The common factor linking these EarthScope objectives is the thermal state of the lithosphere.Heat flow observations provide the strongest observational constraint on the thermal state of thelithosphere. Given the relevance of subsurface thermal conditions to the physical processesgoverning the spatial and temporal variations of lithospheric deformation, a greater knowledge ofthe subsurface thermal regime will contribute greatly to the overall objectives of EarthScopegenerally, and the Plate Boundary Observatory (PBO) experiment specifically. We will collaborate (Oregon State University, University ofUtah and U.S. Geological Survey) in a thermal investigation of the active plate boundary between the Pacific and North American plates in the western United States. Thermal measurements will becollected in PBO boreholes currently scheduled for drilling. The field component consists ofthermal logging and the determination of thermal physical rock properties. Holes will be loggedbetween the end of drilling and the beginning of strainmeter installation so as to not disrupt PBOoperations. Thermal physical rock properties will be measured using modern laboratorytechniques. For both logistical and economic reasons we limit this proposal to boreholes drilledin California which includes important EarthScope targets such as the San Andreas Fault System(SAFS), Long Valley, and Mt. Shasta/Medicine Lake areas. However we will make every effortto log strainmeter boreholes scheduled for drilling in the Pacific Northwest.The importance of thermal processes for EarthScope was highlighted intwo workshops, "Complementary Geophysics", and "Thermal Processes in the Context ofEarthScope". Additionally, the PBO steering committee has recommended that temperatures belogged in strain meter boreholes in the 2004 PBOSC Annual Review. We propose to collect anddisseminate these important data. Broad societal areas of this research include a betterunderstanding of faulting especially the San Andreas, and anthropogenic climate change.Further this proposal fosters collaborations between the academic Earth science community andthe USGS. The proposal will be used to educate and train a graduate student. Results from thisproposal will be disseminated through the EarthScope web site, national and internationalmeetings, and peer reviewed literature.