Site 1155 was located based on 1997 SCS site survey data and confirmed by a short 3.5-kHz PDR and SCS presite survey from the JOIDES Resolution (JR). Onboard instrumentation used included a precision echo sounder, gyrocompass, seismic system, and GPS receivers.
Site selection for Site 1155 was based on a north-south SCS survey conducted during the R/V Melville cruise Sojourner 5 in 1997. A 1.2-hr SCS and 3.5-kHz PDR survey was conducted on the approach to Site 1155 (JR SCS line S3; Fig. F20) to ensure the correct site location. The ship's average speed was 5.0 kt during the survey. The water gun was triggered at a shot interval of 12 s, equivalent to ~31 m at 5.0 kt. Data acquisition and processing parameters were described in "Underway Geophysics" in the "Explanatory Notes" chapter. Survey line S3 was conducted in an east-west direction, perpendicularly across the previous survey line. The final position of Site 1155 is almost identical to the prospectus site AAD-35a and is located at the crossover point of these two survey lines. We marked the position of Hole 1155A near seismic shotpoint 144 of line S3, where the water depth is 4986.4 m (see Fig. F21) and where the sediment cover is apparently thicker than elsewhere. The sediment cover (Fig. F21) extends from 6.70 s to at least 6.85 s in two-way traveltime, equivalent to 150-200 m of sediment. Hole 1155A was drilled through 177 m of sediment before basement was reached, confirming the above estimate. Hole 1155B was shifted ~200 m west of Hole 1155A, near shotpoint 150.