The seismic reflection data were acquired during cruise EW97-09 (Maurice Ewing), the site survey cruise for Leg 199. For all surveys except the first one (proposed Site PAT-14), we used a single 80–in3 [N1] water gun for the seismic source and recorded on the Lamont-Doherty 4-channel streamer. Proposed Site PAT-14 was surveyed with dual 80–in3 water guns to ensure penetration to basement. Shots were spaced at 10 s while the ship speed was maintained at 7-8 kt during the site surveys. The 4-channel data were recorded on a Geometrics engineering seismograph at 0.5-ms intervals for 2 s (after a trigger delay of 5 to 5.5 s) so that the seafloor at each site was within the recording window.
The data shown are stacked and migrated four-channel data, processed using Landmark's Promax software. We used the following parameters: (1) static shift to account for recording delay, (2) normal moveout correction using a constant velocity of 1500 ms, and (3) minimum-phase band-pass filter (40-200 Hz with a 1-octave ramp). The data were then stacked using a diversity-stack algorithm based on the power within a sliding gate of 100 ms. Data were then migrated in the following manner: spectral shaping (15 Hz = 0%, 30 Hz = 100%, 120 Hz = 100%, and 240 Hz = 0%) followed by memory stolt F-K migration using 1500 m/s constant velocity and a stolt stretch factor of 1.