Site 1154 was located based on 1996 single-channel seismic (SCS) site survey data. The location was 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.
3.5-kHz PDRs were used to acquire bathymetric data as well as high-resolution reflection records of the uppermost sediment layers.
Site selection for the third drill site of Leg 187 was based on a SCS survey conducted during the R/V Melville cruise Boomerang 5 in 1996. An ~1.5-hr SCS and 3.5-kHz PDR survey was conducted on approach to Site 1154 (JR SCS line S2; Fig. F8) to ensure the correct site location by comparing the GPS-navigated SCS data with the 1996 SCS image. The ship's average speed was 5.2 kt during the SCS survey. The water gun was triggered at a shot interval of 12 s, equivalent to ~32 m at 5.2 kt. Data acquisition and processing parameters were described in "Underway Geophysics" in the "Explanatory Notes" chapter. Survey line S2 across a local sedimentary basin was conducted back and forth in north-south directions to locate the drill site. The final position of Site 1154 was shifted ~74 m southwest of the prospectus site AAD-16a. We marked this position near seismic shot number 408 of line S2 with a depth of 5747.4 m (see Fig. F9). Acoustic basement was contaminated with reverberations from small-scale relief. However, the sediment cover (Fig. F9) extends from 7.67 s to at least 7.82 s in two-way traveltime, equivalent to 150-250 m of sediment. Hole 1154A was drilled through 233 m of sediments before basement was reached, confirming the above estimate.