Geophysical Site Survey Results: Leg 88
M.S. Grim, J. F. Gettrust · U.S. Government Printing Office eBooks · 1987
This chapter describes the underway geophysical data collected near Site 581.Single-channel (sparker) seismic records from all tracklines and selected high-resolution (3.5-kHz) seismic records are presented.Profiles of magnetic data are displayed with associated bathymetric and acoustic basement profiles.The seismic reflection data, combined with data previously collected in the area, were used to make contour maps of bathymetry and acoustic basement.A map showing echo character types observed on the 3.5-kHz records is included.U.S.N.S. De Steiguer left Adak at 0700L on 27 August 1982 and arrived at Site 581 at 2100L, 31 August 1982.Underway geophysical data were collected by De Steiguer during the site survey phase of the project, during deployment of ocean bottom seismometers, and while shooting for the seismic-refraction crustal studies.Singlechannel seismic reflection data were continuously collected by De Steiguer from 0126Z, 28 August to 0528Z, 10 September, with the exception of the 75 hr.from 0240Z, 5 September to 0540Z, 8 September, when typhoon Gordon passed through the area.Seismic records cover more than 3712 km of trackline.Single-channel seismic reflection data were obtained using a 30-kJ sparker and a 100-m-long hydrophone streamer.Several analog recorders were used.Sweep rates were chosen to obtain both high-resolution records from the upper sediment layers and a complete 10-s (two-way traveltime) sedimentary-acoustic basement section.The seismic records were digitized in the laboratory to obtain bathymetric and acoustic basement depths.Depths are presented in this chapter either as two-way traveltime in seconds or as uncorrected meters assuming a water velocity of 1500 m/s.Final navigation corrections (generally less than 0.5 km) were made by forcing bathymetry and shallow sub-bottom reflectors at track crossings to be in agreement.Data from the Scripps Institution of Oceanography Melville (Antipode cruise, Leg 3), the U.S. Naval Oceanographic Office U.S.N.S. Hunt Cruise 931003, and the D.S.D.P. Glomar Challenger Legs 86 and 88 were integrated with De Steiguer observations to make the contour maps presented in this chapter.The ships' tracklines used for this analysis are presented in Figure 1.The bathymetric data from the Glomar Challenger were provided by D.S.D.P. in digital form.The basement depths were obtained by digitizing tracings made from microfilms of the original Glomar Challenger records.The bathymetric and basement data from the Melville and Hunt cruises were taken from preliminary maps Duennebier, F.