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National Geophysical Data Center


USGS Open File Report 86-339*

Data Announcement 86-MGG-27

     Approximately 900 km of 24-fold Common Depth Point (CDP) seismic-reflection, gravity, magnetic gradiometer, and 3.5 and 12.5 kHz echo-sounding data are now available for purchase from the National Geophysical Data Center (NGDC) for the continental margin of Wilkes Land, Antarctica. Gravity and bathymetric data are also available form the transit line between Wilkes Land and New Zealand. The data were collected in 1984 by the U.S. Geological Survey R/V S.P. LEE. The seismic data source was a 5- airgun array totaling 1,311 cu. in., pressurized to 2,000 psi, towed at a depth of 10.5 m. The receiver consisted of a 24- channel hydrophone streamer, with 100-m group lengths containing 60 hydrophones i each group. The near channel offset from the airguns was 297 m. The data were recorded with a GUS Model HDRR- 4200 recording system.

     The magnetic gradiometer data were recorded continuously with a Geometrics proton-precession marine gradiometer. Two proton-precession magnetometers, separated horizontally by 150 m, were towed aft of the ship. The near sensor was towed 300 m aft, and both sensors were towed at a depth of approximately 50 m. Data were measured at 4-sec intervals. The gravity data were recorded continuously with a LaCoste and Romberg sea gravimeter on a 2-axis stabilized platform. Data were collected at 20-sec intervals and later desampled to 2 min or greater for plotting and modeling. All digital navigation, bathymetry, gravity, and magnetic gradiometer data have been condensed into a single file "MGD77".** Minor modifications to the MGD77 format were required to accommodate the inclusion of the gradiometer reconstructed magnetic data. The geophysical data record contains the total field values for the gradiometer sensors, but the residual field is calculated from the gradiometer reconstruction rather than from individual sensors, and the temporal variations have been removed from the residual field. The CDP stack tapes of the multichannel seismic data in SEG-Y format are also available for purchase from NGDC. These data were made available by the U.S. Geological Survey for public dissemination.
* "Marine Geophysical Data from the Wilkes Land Continental Margin, Antarctica," S.L. Elttreim, M.A. Hampton, G.L. Smith, and J.R. Childs, 1986, USGS Open File Report 86-339, U.S. Geological Survey, Menlo Park, CA.

** "The Marine Geophysical Data Exchange Format - 'MGD77' (bathymetry, magnetics, and gravity)," Key to Geophysical Records Documentation No. 10 (Revised), 1981, National Geophysical Data Center, NOAA, Boulder, CO 80303.


     Analog Data:

         17 Sections of the stacked multichannel seisic-reflection profiles at a horizontal scale of 1 km/in., and a 2-way travel-time scale of 1.5 in/sec). Available in plastic sepia, paper sepia, and blackline.

         17 Sections of navigation, bathymetry, free-air gravity, and magnetic gradiometer profiles plotted at a horizontal scale identical to the multichannel seismic-reflection data: available in plastic sepia, paper sepia, and blackline.

         1 shot-point navigation map available in plastic sepia, paper sepia, and blackline.

     Digital Geophysics Data:

         Navigation, bathymetric, gravity, magnetic gradiometer data, and shot-point numbers:

            1 magnetic tape (9-track, 1600 bpi, ASCII) Also available on CD-ROM

     CDP Stack Tapes:

         15 Demultiplexed magnetic tapes (6250 bpi, SEG-Y format) 85 Sort tapes

Please contact NGDC for prices.