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National Geophysical Data Center

MULTICHANNEL SEISMIC-REFLECTION PROFILES

Tonga Region - South Pacific

USGS Open File Report 86-457*

Data Announcement 87-MGG-10

Approximately 2,325 km of 24-channel seismic-reflection profiles across the Lau Basin, Tonga Ridge, and Tonga Trench in the Tonga region of the south Pacific are now available for purchase from the National Geophysical Data Center (NGDC). These data were collected in early April 1982 by the U.S. Geological Survey (USGS) Research Vessel S.P. LEE during Cruise L582SP. The profiles were collected as part of the Australia-New Zealand- United States Tripartite Agreement of 1982 in cooperation with the Ministry of Lands, Survey, and Natural Resources of the Kingdom of Tonga. The USGS, Department of Interior has provided these data to NGDC for public dissemination.

The seismic energy source consisted of a tuned array of five airguns with a total volume of 1,313 cu. in. of air compressed to approximately 1,900 psi. The recording system consisted of a 24- channel, 2,400-m long streamer with a group interval of 100 m, and a GUS (Global Universal Science) model 4200 digital recording instrument. Shots were fired every 50 m with 100-m group intervals.

Navigational control for the survey was provided by a Magnavox- integrated navigation system using transit satellites and Doppler sonar. A 2-msec sampling rate was used in the field and the data were later desampled to 4 msec during the demultiplexing process. Eight seconds of data length were recorded which, combined with a deep-water delay, yielded up to 16 sec of two-way travel time. The sequential processing of data was editing-demultiplexing, velocity analysis, CDP stacking, deconvolution-filtering, and plotting on an electrostatic plotter. The seismic lines are available on plastic, paper sepia, paper blackline, or on magnetic tape.

* Multichannel Seismic-Reflection Data Collected in 1982 in the Tonga Region of the South Pacific," by Dennis M. Mann, David W. Scholl, and Ray W. Silter, USGS Report 86-457, U.S. Geological Survey, Menlo Park, CA 94025.

DATA AVAILABLE

Tonga Region - South Pacific

     16 tracklines/24 sections, 2,325 km

          (plastic sepia)  Product #976F20157
          (paper sepia)  Product #976F19157
          (blackline)    Product #976A18157
Digital Geophysics Data:

          Digital Shot-Point Navigation - 1 magnetic tape
          (9-track, 1600 bpi, ASCII).  Product #976H07157.
          This is also available on CD-ROM, Product #129F27001
CDP Stack Tapes:

          16 digital demultiplexed magnetic tapes.  Product
          #976L07157.

          16 digital stacked magnetic tapes.  Product #976L07158.

Please contact NGDC for prices.