Marine Geoscience Data System
Malawi_PROBE Seismic Reflection/Refraction
Selected Processed 2-D Multi-channel Seismic Reflection Data from Lake Malawi (Nyasa) Acquired by Project PROBE (Duke University) in 1986-1987 (legacy time processing)
This data set is a collection of 10 time-processed structural-dip profiles acquired along the length of the Lake Malawi (Nyasa) Rift (Malawi, Tanzania, Mozambique) as part of the PROBE project (Proto-Rifts and Oceanic Basin Evolution). The data files are in SEG-Y format, 6 seconds two-way travel time record length, 4 ms sample rate. Profiles are generally oriented east-west across multiple rift segments. Data were acquired aboard R/V Nyanja, a 36-foot-long dedicated geophysical vessel transportable by cargo aircraft. Source was a single 140 cubic inch EERI airgun, or 3x40 cubic inch array of GSI sleeve guns. Streamer was a GECO custom-built 960 m active-length cable comprising 48 groups (20 m group interval); lead-in cable length varied from 250-440 m. Streamer depth was nominally 10 m and controlled a buoy suspension system. Fold coverage was nominally 24-fold. Acquisition was via Texas Instruments DFS-V, at 2 ms sample rate. Navigation was by transit satellite, radar, automatic speed log and deduced reckoning. Processed navigational data are embedded in SEG-Y trace headers. Navigational accuracy ranges from <100 m to several km in places. Every line is controlled by a minimum of two fixes and a 40-80 km line is controlled by 5-8 good fixes. Chief Scientist was Bruce R. Rosendahl. Data were recovered from 9-track tape and archived on modern media under the supervision of Christopher A. Scholz, Syracuse University. Legacy time processing at Duke University was completed with Digicon DISCO 50 software on a DEC VAX 11/750 computer, applying the following workflow: Demultiplexing, Resample, Geometry Definition, Trace Edit, Sort, Deconvolution, Filter, Velocity Analysis, Stacking, Mute, Migration, Display. Deconvolution is a predictive gap deconvolution, occasionally spiking deconvolution is used. Filtering was variable, typically a bandpass filter with a Hanning taper was employed with typical cutoffs of 6-10 Hz at the low end, and 50-55 Hz at the upper end. Some lines received time-variant filtering and occasionally notch filters were used. Select lines were subjected to a post-stack finite difference time migration routine. Funding for data collection and processing was from multiple 1980s-era oil and gas companies.
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The data have been processed/modified to a level beyond that of basic quality control (e.g. final processed sonar data, photo-mosaics).

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