Site location for Site 1161 was based on a Leg 187 single-channel seismic survey conducted during the transit from Site 1158 to Site 1159 (JOIDES Resolution survey line S7; Fig. F13 in the "Site 1159" chapter). The roughly north-south seismic profile between shotpoints 1074 and 1283 shows a ~1.6-km-wide basin structure, centered near shotpoint 1205 (see site AAD-38a in Fig. F15 in the "Site 1159" chapter). The proposed site (AAD-38a) is near shotpoint 1200, located slightly toward the northern side of the basin.
An additional 0.9-hr 3.5-kHz PDR survey was conducted on approaching the site. Because of an unknown navigation problem, the apparent position of the basin structure was found to be shifted ~1 km northward relative to the position derived from the seismic profile. Hole 1161A, ~0.5 km north of the proposed site, is in a location corresponding to shotpoint 1216 of the S7 seismic profile. Sediment cover at this position is from 6.77 to 6.87 s two-way traveltime, equivalent to at least 100 m of sediment (see Fig. F15 in the "Site 1159" chapter). Before basement was reached, we washed through 116 m of sediment in Hole 1161A, whereas about 220 m to the north in Hole 1161B, we penetrated 158.5 m sediment. Both thicknesses are consistent with estimates from the seismic profile.