Seven reliable determinations of downhole temperatures were made at depths between 35 and 284 mbsf in Hole 1173A using the Adara APC temperature tool, the WSTP, and the DVTP. Table T25 summarizes the deployments, and the station data are shown in Figures F50 and F51. Measurements were not attempted deeper in the hole because the formation became sufficiently stiff that it probably would have been cracked by even the streamlined probe tip of the DVTP.
As described in "In Situ Temperature and Pressure Measurements" in the "Explanatory Notes" chapter, in situ temperatures were estimated by extrapolation of the station data to correct for the frictional heating on penetration, using an average thermal conductivity of 1.0 W/(m·°C) (see "Physical Properties"). The estimated in situ temperatures from all three tools define a linear gradient of 0.183°C/m in the upper 300 m (Fig. F52), yielding a conductive heat flow of ~180 mW/m2 at Site 1173. This value is generally consistent with, but slightly higher than, prior determinations of high heat flow near the toe of the Nankai accretionary prism in the vicinity of the Leg 190 transect (e.g., Kinoshita and Yamano, 1986; Yamano et al., 1992). Deeper than 300 m, thermal conductivities increase by 30%-50%, so the gradient should decrease proportionally, and in situ temperatures of ~110°C are estimated for the bottom of the hole (Fig. F52).
Pressures were also recorded during the two DVTP-P deployments at 198 and 284 msbf (Fig. F53). As noted in "In Situ Temperature and Pressure Measurements" in the "Explanatory Notes" chapter, postcruise modeling and processing is required to estimate in situ pressures, but preliminary examination of the raw data seems only to indicate a hydrostatic pressure differential between the two stations—not unexpected at these relatively shallow depths at the reference site, outboard of the active tectonic domain in the accretionary prism.