Abstract

Three refraction profiles were shot in the Gulf of Mexico 100 nautical miles south of Galveston. Recordings were made using free floating and anchored sonobuoys deployed near an ocean bottom seismograph (OBS). Explosions and airgun sources were used. Vertical component geophones with resonant frequencies of 4.5 Hz and 8 Hz were used in the OBS system.We compared seismic data recorded by the conventional sonobuoy and the OBS. The signal-to-noise ratio for the OBS is about three to four times better than that of the sonobuoy, facilitating the interpretation of the three profiles.Based on the first and later arrivals obtained from the OBS records, traveltime curves and an amplitude distance curve are constructed. The results show that the velocities at the experimental sites vary between 1.7 km/sec at the surface to 7.7 km/sec at a depth of 14.5 km. The 7.7 km/sec layer may be lower crust or anomalous mantle. The low velocity sediments (1.7 - 3.3 km/sec) thicken westward from the deployment point.

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