National Centers for Environmental Information (NCEI)
MULTICHANNEL SEISMIC-REFLECTION DATA
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 for purchase from
the National Geophysical Data Center (NGDC) (now the National Centers for Environmental Information (NCEI)) 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 (now NCEI). 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 (now the National Centers for Environmental Information), NOAA, Boulder, CO 80303.
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