2. UNDERWAY GEOPHYSICS ON LEG 101 1

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1 . UNDERWAY GEOPHYSICS ON LEG Christian A. Auroux, Ocean Drilling Program, Texas A&M University, College Station, Texas and Shipboard Scientific Party INTRODUCTION Routine geophysical measurements were collected at intervals during Leg. Of the 88 n. mi covered by the leg, geophysical data were collected only as follows: () ODP Line, Miami, Florida, to Site ; () ODP Line, Site to Site 7; () ODP Line, southeastern entrance to Exuma Sound to Site ; and () ODP Line, Site to Site. We were under way 5. days or % of the time spent at sea. The on-board instrumentation included two precision echo sounders, seismic-reflection profilers, a TRANSIT satellite navigation system, and LO RAN C. The instruments were maintained and operated by the ODP marine technicians in cooperation with the scientific party and the officers and crew of SED- CO-FOREX, Inc. Because of technical and electronic problems during Leg, no magnetic data are available. Austin, J. A., Jr., Schlager, W., Palmer, A. A., et al., 8. Proc, Init. Repts. (Pt. A), ODP,. Address: Ocean Drilling Program, Texas A&M University, College Station, TX 7. James A. Austin Jr. (Co-Chief Scientist), Institute for Geophysics, University of Texas at Austin, Austin, TX ; Wolfgang Schlager (Co-Chief Scientist), Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL (current address: Vrije Universiteit, Instituut v. Aardwetenschappen, Postbus 7, 7 MC Amsterdam, Netherlands); Amanda A. Palmer, Staff Scientist, Ocean Drilling Program, Texas A&M University, College Station, TX 7; Paul A. Comet, The University, Newcastle-Upon-Tyne, Newcastle, United Kingdom (current address: Core Labs Singapore, A-Lim Teck Boo Rd., Singapore 5); Andre Droxler, Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL (current address: Department of Geology, University of South Carolina, Columbia, SC 8); Gregor Eberli, Geologisches Institut, ETH-Zentrum, Zurich, Switzerland (current address: Fisher Island Station, University of Miami, Miami, FL ); Eric Fourcade, Laboratoire de Stratigraphic Universite Pierre et Marie Curie, Place Jussieu, Paris Cedex 5, France; Raymond Freeman-Lynde, Department of Geology, University of Georgia, Athens, GA ; Craig S. Fulthorpe, Department of Geological Sciences, Northwestern University, Evanston, IL ; Gill Harwood, Department of Geology, The University, Newcastle-Upon-Tyne, NE 7RU United Kingdom; Gerhard Kuhn, Geologisches Institut Gottingen, Federal Republic of Germany (current address: Alfred Wegener Institut fur Polarforschung, Columbus Center, D- Bremerhaven, West Germany); Dawn Lavoie, NORDA Code, Seafloor Geosciences Division, NSTL, MS 5; Mark Leckie, Woods Hole Oceanographic Institution, Woods Hole, MA 5 (current address: Department of Geology and Geography, University of Massachusetts, Amherst, MA ); Allan J. Melillo, Department of Geological Sciences, Rutgers University, New Brunswick, NJ 8 (current address: Chevron U.S.A., New Orleans, LA 7); Arthur Moore, Marathon Oil Company, P.O. Box, Littleton, CO 8; Henry T Mullins, Department of Geology, Syracuse University, Syracuse, NY ; Christian Ravenne, Institut Francais du Petrole, B.P., 5 Rueil Malmaison Cedex, France; William W. Sager, Department of Oceanography, Texas A&M University, College Station, TX 7; Peter Swart, Fisher Island Station, University of Miami, Miami, FL (current address: Marine Geology and Geophysics, Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL ); Joost W. Verbeek, Dutch Geological Survey, P.O. Box 57, A.D. Haarlem, Netherlands; David K. Watkins, Department of Geology, University of Nebraska, Lincoln, NE 88; Colin Williams, Borehole Research Group, Lamont-Doherty Geological Observatory, Palisades, NY. NAVIGATION Navigation data were collected on the bridge by a Magnavox MX7A TRANSIT satellite receiver and a LORAN C. Positions were obtained with this system throughout the entire leg (Table ). BATHYMETRIC-DATA RECORDING Bathymetric data were obtained with.5-khz and -khz echo sounders, using a Raytheon recorder system for the.5-khz and an EDO 8C recorder for the -khz. Unfortunately, as a result of poor placement of hull-mounted transducers relative to thrusters used for dynamic positioning, the quality of the recorded data is very poor. SEISMIC-REFLECTION PROFILES In this chapter, we present the seismic lines collected during Leg. These data were recorded with the following equipment and techniques. Sources The seismic sources used aboard the JOIDES Resolution during Leg were one -in. water gun and one or two 8-in. water guns (see Table for details). Streamer Hydrophones Either of two Teledyne streamers are available on winches at the fantail. Each contains hydrophones and is m long. The streamers are towed approximately m behind the vessel. The towing depth was set by external depth depressors ("birds"). The hydrophone elements are then combined to procure a single signal. Data Recording The central part of the acquisition/processing system was a super-micro 5 Masscomp computer. It allowed data to be processed and displayed in real time on a 5-in.-wide Printonix highresolution graphic printer ( dots per in.). The raw data were recorded on a Cither tape, using an SEG-Y format and a density of bits/in. Seismic data were also displayed in real time in analog format on two EDO 55 dry-paper recorders, using only streamers, amplifiers, and two band-pass filters (see Table and Fig. ). SEISMIC-LINE REPROCESSING ODP lines and, recorded with the Masscomp computer, were reprocessed during the site occupation (reprocessing treatments applied are described in Table ). The final data (see Fig. 5, Site chapter, and Fig. 5, Site 7 chapter, this volume) were 5

2 C. A. AUROUX, SHIPBOARD SCIENTIFIC PARTY displayed on a -in.-wide Versatec plotter ( dots per in.) with the following parameters: Traces per inch:. Clip high:. in. Clip low: -. in. Deflection:. in. Plot start time: 5 ms. Plot stop time: 5 ms. area display. Positive peaks to the right. ACKNOWLEDGMENTS The scientific party of Leg thanks Mark Weiderspahn and Ali Tufayli of the University of Texas at Austin, who designed and wrote the seismic digital acquisition system. Table. Navigation data for Leg. Day Month Year Time (UTC) a North latitude '> West longitude Cumulative distance (n. mi) , Actual Drift speed reckoning Comments b A A B C C D D No

3 UNDERWAY GEOPHYSICS ON LEG Table (continued). Day 7 8 Month Year Time (UTC) a North latitude West longitude Cumulative distance (n. mi) Actual Drift speed reckoning Comments b 7A 7A 7B 7B 8A 8A A A A A B B C C No

4 C. A. AUROUX, SHIPBOARD SCIENTIFIC PARTY Table (continued). Day Month Year Time (UTC) a North latitude West longitude Cumulative distance (n. mi) Actual Drift speed rec koning Comments No

5 Table (continued). UNDERWAY GEOPHYSICS ON reckoning Comments b No S S S A A B B S S S S sail 5A 5A 5B 5B 5B 5B UTC = Universal Coordinated Time. = LORAN C navigation; = change of course; = satellite navigation. North West.-,... Actual ~.,..., l t d Cumulative Drift Time!_!^ distance speed Day Month Year (UTC) a (n. mi)

6 CA. AUROUX, SHIPBOARD SCIENTIFIC PARTY Table. Real-time recording parameters for seismic-reflection profiles. Line Line Line Line Start at: End at: Source: Streamer: Miami Site One -in. water gun Port + stbd Site Site 7 Two 8-in. water guns Port Exuma Sound Site Two 8-in. and one -in. water guns Port Site Site Two 8-in. water guns Port Table. Parameters for seismic-line reprocessing. Line Line EDO : Data window: 5 to 5 ms 5 to 5 ms High cut: Low cut: Gain: Amp: Recorder: Hz Hz db Hz Hz 8 db Hz Hz 8 db Hz 5 Hz AGC: Response time: Start time: Gain: 5 ms ms % Zero phase band-pass : filter: 5 ms ms % EDO : High cut: Low cut: Hz Hz Hz Hz Hz Hz 5 Hz 8 Hz High cut: Low cut: 5 Hz Hz Gain: Amp: Recorder: db 8 db 8 db

7 UNDERWAY GEOPHYSICS ON LEG ;sw BAH--A (Site ) Vertical exaggeration: approx. X hr. = 8n.mi./.8 km. Jfi; Beacon dropped at 7 L Time of day (hours, local time) 5 L z xuma Sound SftW ;i/?v! ' Target horizon Figure. Analog version of seismic line, Exuma Sound to Site. One -in. water gun was firing before hr local time (L), one 8- in. water gun was firing from to 5, and two 8-in. water guns were firing after 5.