Logging operations in Hole 1173A are described in Shipboard Scientific Party (2001b). For this work, it is important to note that two passes of the DSI were made over the interval from 65 to 360 m below the seafloor (mbsf) through lithostratigraphic units composed of sandy to muddy turbidites, some volcanic ash, and silty and siliceous claystones (Shipboard Scientific Party, 2001d). The hole was drilled with a 9.875-in bit that was raised to a depth of 65 mbsf prior to logging. The logging tool was not able to reach the total drilled depth in Hole 1173A due to bridging of the hole at 380 mbsf, and efforts to clear this obstruction deteriorated the shallow hole conditions to some extent. Before logging, 50 bbl of sepiolite mud was pumped into the hole, and then, to further stabilize the hole, ~225 bbl of 10.5-ppg weighted barite mud was pumped in the hole to 637 mbsf (well below the first log reading). As a result, the borehole fluid properties and any change in fluid invasion into the formation are likely to be similar between the two passes. Both of the DSI passes were run at the same logging speed using the wireline heave compensator (Goldberg, 1990). Pass 1 recorded the high-frequency upper dipole plus P- and S-wave modes, and pass 2 recorded the low-frequency lower dipole plus P- and S-wave modes. The low-frequency (<1 kHz) dipole source was used for the second pass to enhance the flexural wave energy.
In Figure F2, the caliper log shows the hole diameter in orthogonal directions from both logging passes. Hole diameter is variable and enlarged from 100 to 220 mbsf along one axis and otherwise relatively constant to a depth of 360 mbsf. The measured shape of the borehole remains essentially unchanged between passes. Enlarged and rugose borehole conditions, such as those observed in the upper interval, degrade sonic logging data (e.g., Goldberg et al., 1984).