Single-channel seismic reflection profiles were collected prior to drilling of ODP Leg 165. A 1992 seismic survey over Site 1000 was conducted aboard the Cape Hatteras. Seismic data over Sites 998 and 1001 were collected as part of a 1994 ODP site survey aboard the Maurice Ewing. These seismic sections are compared with results generated from data accumulated during Leg 165. These data include physical properties measurements of velocity and density, downhole logs, and lithostratigraphic core descriptions (Sigurdsson, Leckie, Acton, et al., 1997).
During April and May of 1992, research Cruise CH9204 aboard the Cape Hatteras was completed as part of a study of Pedro Channel and Serranilla Basin on the northern Nicaraguan Rise. Over 2300 km of digital, high-resolution single-channel seismic reflection (SCS) data was obtained in Pedro Channel using an 80-in3 GI air gun from Seismic Systems Inc. as the seismic source. The GI gun was fired every 7-10 s at a ship speed of 5.5 kt and digitized at a 1 ms sampling rate, using the Rice University Elics/Delph 1 system. Navigation for the SCS data consists of Global Positioning System (GPS) fixes roughly every 30 shots.
The single-channel seismic reflection data sets over Sites 998 and 1001 were collected during research Cruise EW9417 in December of 1994 aboard the Maurice Ewing. Approximately 270 km of SCS data in the vicinity of Site 998 and 335 km of SCS data near Site 1001 were acquired using two 80-in3 SSI water guns fired every 10 s as an energy source and digitized at a 1-ms sampling rate with the Rice University Elics/Delph 2 acquisition system. GPS fixes are available at each shotpoint.
Processing and display of the SCS data was completed in the Rice University Geology and Geophysics Department. ProMAX Version 6.0 on an IBM RS6000 was used to process the data. A typical processing flow included trace equalization, hand statics corrections, removal of noisy traces, band-pass filtering (25-50-200-400 Hz), 200-ms Automatic Gain Control (AGC), water bottom mute, and variable displays. Because the water guns used in the EW9417 data acquisition were out of phase, a predictive deconvolution with an 80-ms operator length was applied to the EW9417 data to compress the multipeaked source signal. The dominant frequency of both seismic data sets is ~100 Hz and results in a theoretical seismic resolution of 4-10 m (based on sediment velocities of 1600-4000 m/s.
Sonic and density logs as well as physical properties measurements from Leg 165 (Sigurdsson, Leckie, Acton, et al., 1997) were used in creating the synthetic seismograms. Physical properties measurements of velocity were obtained using the digital sonic velocimeter (DSV) on unconsolidated sediments and the Hamilton Frame on samples that were too consolidated for use on the DSV (Sigurdsson, Leckie, Acton, et al., 1997). Wet bulk density measurements were collected as part of index properties measurements. Descriptions of the sediment recovered during coring operations were compared with reflection patterns on the synthetic seismogram and SCS seismic facies. Biostratigraphy for the cored intervals provided age control.