2 Materials and Methods Temperature DataTemperature data were collected with 55 miniature temperature loggers (MTLs): 10 TDR-2050s and 15 TR-1050s manufactured by RBR Ltd. (Canada; www.rbrglobal.com/) and 30 Antares 1357 high-pressure data loggers manufactured by Antares Datensysteme GmbH (Germany; www.antares-geo.de/). Each of the MTLs has an autonomous data logger and a temperature sensor enclosed within a titanium casing pressure rated for up to 10,000 m water depth. The TDR-2050s also have a pressure sensor that effectively records the sensor's water depth inside the cased borehole. The MTLs were attached to spectra rope and wrapped with a rubber protective covering. The sensor string was attached to a hanger and hung within 4.5" steel tube casing with a check-valve at the bottom that prohibited fluids from flowing into the casing from below. Spacing between sensors varied from 1.5 m at the bottom near the fault zone to 3 m, 6 m and greater intervals higher up. The sensors recorded every 10s, 20s or 10 minutes depending upon the model. The RBR temperature sensors have precision of <0.00005°C and the Antares 0.001°C. In addition to factory calibration constants, each temperature sensor was calibrated using a Hart Scientific water bath containing a mixture of ethylene glycol and water and an NIST reference temperature probe over 8 or more different temperatures from 0 -30 o C and spanning the range recorded during the JFAST experiment. The resulting sensor corrections permit accuracy for all temperature sensors to within ~0.001 o C. Reliable corrections could not be obtained for sensors at 744.77 and 805.17 mbsf. The absolute temperatures for these two sensors may be off by a few 10 -3 o C , although their residual temperatures appear consistent with neighboring data. Additional details regarding the sensors and observatory are described in (13). Thermal PropertiesKnowledge of thermal-physical rock properties is important for interpreting the temperature data. Differences in thermal conductivity may lead to steady-state perturbations in the background geothermal gradient. Estimates of the thermal diffusivity are important for interpreting an observed temperature anomaly from frictional heating, and volumetric heat capacity controls the relationship between heat and temperature. We utilize thermal property measurements taken on core material from borehole C0019E that cover lithologic and depth intervals that correspond to the regions covered by sensors in the observatory. Thermal conductivity values consist of 45 shipboard measurements on split cores using a TEKA thermal conductivity half-space probe (13). An additional 38 discrete samples were also measured using a divided bar system revealing similar results. Four large samples were also measured using the transient plane heat source method revealing very little anisotropy in thermal conductivity. Thermal diffusivity and heat capacity measurements were also determined for these four samples. The lowermost three samples are most representative of the intervals...

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