National Geophysical Data Center
IPOD SITE SURVEYS
Data Announcement 83-MGG-13
Multichannel seismic reflection data profiles are now available for the area across the Nankai Trough south of Shikoku Island, Japan. The Japan Oceanographic Data Center, in cooperation with the Ocean Research Institute of the University of Tokyo and Japan Petroleum Exploration Company (JAPEX), has provided these data to the National Geophysical Data Center for public dissemination.
These data were obtained in December 1980 as part of the Japanese International Phase of Ocean Drilling (IPOD) activities to help select appropriate drilling sites in the Nankai Trough.* The data were collected aboard the M/V KAIYO-Maru using 20 airguns (total volume of 2,090 cubic inches) fired simultaneously. The airguns were towed 55 m behind the ship's antenna and 10 m below the sea surface and were operated at a pressure of 2,000 psi. The array of airguns were fired once every 50 m (approximately 16 sec). The reflection signals were received by a 32-group hydrophone array 2.4 km long and were then recorded on a 48- channel recorder and a single-channel analog recorder.
The digital tapes obtained were processed to include demultiplex with recording gain removal: common reflection point gather; digital automatic gain control; pre-NOM deconvolution with prediction distance of 4 msec, autocorrelation gate of 2 sec, and operation length of 120 msec; stacking velocity analysis at every 5 km; normal moveout correction (NMO) and 24-fold stacking; predictive deconvolution with predictive distance of 4 msec, autocorrelation gate of 3 sec, and operation length of 320 msec. The seismic profile data are available either as hard copies or on magnetic tape.
* Multi-Channel Seismic Reflection Data Across Nankai Trough, POD- Japan Basic Data Series, No. 4, Ocean Research Institute, University of Tokyo, February 1982.
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