OCEAN-BOTTOM SEISMOGRAPH PRODUCTION AND GULF OF MEXICO DATA ANALYSIS
TEXAS INSTRUMENTS INC DALLAS SCIENCE SERVICE DIV
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Six additional Ocean-Bottom Seismographs, similar in design and functionally interchangeable with existing units, were produced. Results of testing the new units showed that system performance is not measurably affected by the unit modifications and that the replacement Hall-Sears seismometer package is operationally similar to the EV-17 but is more dependable. Shallow bottom sediments in the test area are highly layered, supporting several propagation modes. Shear velocities vary rapidly in these shallow sediments. Very low-velocity Rayleigh-type wave motion is observed from explosions, following refracted arrivals and higher-velocity normal modes these low- velocity arrivals are probably dispersive Stoneley waves. Signal energy on the horizontals immediately following the refracted arrivals is a combination of leaking modes and shear modes. The dominant ambient noise appears to be isotropic and of low velocity this results from unusually well-defined shallow mud layers and may serve to explain much of the difference between ocean-bottom and land recordings.