USGS1989
In August 1979, the U.S. Geological Survey (USGS) aboard the M/V SEISMIC EXPLORER of Seismic Explorations International (SEI), ran 17 lines (1,270 km) of multichannel, seismic-reflection profiles on the western Florida Shelf. The main features of the SEI system were (1) a digital recorder with an instantaneous-floating-point-gain constant of 24 dB, (2) a 64-channel hydrophone streamer, 3,200 m long, and (3) a 21-airgun array that had a total volume of 2,000 in and a pressure of 2,000 psi. Sampling interval was array to the center of the farthest phone group was 3,338 m and to the nearest phone group, 188 m. Shot points were 5O m apart to obtain a 32-fold stack. Navigation was by an integrated satellite/Loran/doppler-sonar system. The SEI data were processed by Geophysical Data Processing Center, Inc. of Houston, Texas. Processing procedures were standard with the following exceptions: (1) a deringing deconvolution that had a 128-ms operator length was done prior to stacking. (2) a time-variant predictive deconvolution that had a filter operator length of 100 ms and automatic picking of the second zero-crossing was applied after stacking to further suppress multiple energy. (3) Velocity analyses were performed every 3 km, using a technique that included the determination and consideration of both the amount and direction of apparent dip. (4) Automatic gain ranging using a 750-ms window was applied pre- and post-stack. ( 5) Lines affected by sea floor's angle of slope were deconvolved again before stacking and time-variant filter parameters were adjusted to follow the sea-floor geometry. The data taken with the 3,200-m streamer and 2,000 in 3 airgun array, aboard M/V SEISMIC EXPLORER (Arabic numerals) are vastly superior to those obtained by R/V GYRE using a much smaller streamer and source (Roman numerals). The former consistently show coherent primary events from within the units underlying the Mesozoic section on the western Florida Shelf, while the latter tend to do so only in the inshore area where pre-Mesozoic basement occurs at depths of less than 2 km. The R/V GYRE data were open filed previously (Ball and others, 1987). A synthesis of both sets of data is included in Ball and others (1988). Reflectors correlate to the full 8-s duration of recording time. A number of lines were restarted due to equipment failure; no areas were omitted, however, shotpoints overlap. The original records may be seen at the USGS branch of Atlantic marine geology offices in Woods Hole, Mass. Copies of the multichannel data may be purchased only from the National Geophysical Data Center, NOAA, Code E64, 325 Broadway, Boulder, CO 80303 (tel. 303/497-6345).