Explosion Sounds in Shallow Water
Seismic investigations of various water-covered areas by the refraction method are described. These areas were chosen for their diverse geologic columns. The instrumentation was such that frequencies from 10 cycles per second to 10,000 cycles per second were investigated and analyzed. Intensity measures of the various frequencies were also made. Recordings were made using geophones and hydrophones for sound receivers.
The water-borne sounds in 10 and 20 fathoms of water showed marked frequency dispersion, although sounds originating in very deep water showed no dispersion when recorded in shallow water. The dispersion appears to be governed by the water depth and the bottom material. No water-borne sounds were originated when shots were placed on land or when land intervened on a straight path from shot to receiver. High frequencies disappear more rapidly with distance than low frequencies.
Oscillations of the explosive gas bubble were observed and time intervals checked with present theory. The pulse sounds produce all the phenomena of the original explosion except that each succeeding pulse seems to have a lower high-frequency limit.
All the important ground-borne sounds were found to be below 100 cycles per second. No correlation of intensity to transmission layer could be discerned except in one case.
Refraction profiles were laid as near as possible along the strike of the structures. Reversals on profiles were available only twice, so that slopes were not determined. Depths to the basement complex were 3130 feet at Solomons, Md., shoal; 3080 feet at Solomons, Md., deep; 6400 feet at Jacksonville, Fla., shoal; 7730 feet at Jacksonville, Fla., deep; 1380 feet at Virgin Islands, shoal; 1710 feet at Virgin Islands, deep; > 16,600 feet at Barbados; 12,210 feet at Orinoco, shoal; 22,790 feet at Orinoco, deep. Travel-time curves are included for each location. Interpretation of the seismic results is made with some aid from the known geology.