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National Centers for Environmental Information (NCEI)


Data Announcement 91-MGG-01

In 1982, a geophysical survey in the territorial waters of Vanuatu was conducted by the U.S. Geological Survey's R/V S.P. Lee (cruise identifier L6-SP-82). These data for purchase from the National Geophysical Data Center (NGDC) (now the National Centers for Environmental Information (NCEI)).

Approximately 2400 km of 24-fold multichannel seismic reflection data were collected along 40 lines. The seismic source consisted of a tuned, 5 airgun array totaling 1311 cubic inches, pressurized to 2000 psi, towed at a depth of approximately 10.5 meters. Individual gun volumes were usually 148, 194, 194, 309, and 466 cubic inches. The receiver consisted of a 24 channel hydrophone in each group. The near channel offset from the airguns was 297 m and far channel offset 2611 m. The data were recorded with a GUS model HDDR-4200 recording system.

Shots were fired every 50 meters and records were sampled in the field at a 2 millisecond rate but resampled to a 4 millisecond rate prior to processing. Primary navigation was by satellite.

The basic data processing sequence was editing-demultiplexing, static corrections, CDP sort, velocity analysis, NMO correction, stacking, and plotting on an electrostatic plotter. Particular attention was devoted to accurate velocity estimation through the use of standard semblance plots and constant velocity stacks. The semblance velocity analyses were performed every 2.5 km (50 CDP's) along each line, using a summation of 3-5 adjacent CDP gathers for each analysis. The seismic lines are available on plastic, paper sepia, paper blackline, and magnetic tape.

Digital geophysical data from this cruise are also available from our office. To complement the seismic data, there are 2375 nautical miles of bathymetry data, 2216 nautical miles of magnetic data, and 2302 nautical miles of gravity data. The data are formatted in the standard MGD77 format and available as 1600 or 6250 bpi and in ASCII or EBCDIC code tapes.

* Greene, H.G., Macfarlane, A., Smith, G.L., and Geist, E.L., Multichannel Seismic-Reflection Profiles from Vanuatu Collected in 1982, Open File Report 90-100, U.S. Geological Survey, Menlo Park, California.

DATA AVAILABLE (please refer to 9-digit product numbers when ordering)

41 multichannel seismic-reflection profiles for 40 lines
      (plastic sepia) Product #976F20179
      (paper sepia) Product #976F19179
      (blackline) Product #976F18179

2 trackline charts (scale: 1.5 inches = 10 nautical miles)
      Product #976A18179

1 magnetic tape containing shotpoint navigation, magnetics, bathymetry, and gravity. Product #976H07179. This is also available on CD-ROM, Product #129F27001.

40 digital stacked tapes in SEG-Y format. Product #976L07179