Implosive Source Research Articles

Method and device for initiating an underwater implosive source

First Page

Seismic events with non-shear component: II. Rock bursts with implosive source component

The rock burst mechanism of an implosive character is introduced and discussed; it is based on the idea that the compressional component of the stress field around the loaded stress concentrator can participate in the rock burst event. For easier classification of the rock burst from this viewpoint, a set of P-wave radiation patterns of the rock burst with a varying portion of the implosive component and varying propagation velocity of the displacements is presented and discussed. To support the credibility of the rock burst mechanism of an implosive character the seismic signals of the rock bursts from the mid-Bohemian coal district with negative signs of the P-wave first onsets are presented.

Ultrabroadband target strength measurements of biological entities

An ultrabroadband underwater echo‐ranging system has been employed to collect echoes from biological entities off the coast of Southern California. The system uses an implosive impulse source and a broadband, constant beamwidth towed array. For these measurements, target strengths were calculated over the band of frequencies from 500 Hz to 50 kHz with minimal distortion due to transducer beamwidth effects. Averaged frequency spectra for echoes from many biological targets have been examined. Echoes from schools of fish exhibit Rayleigh scattering regions as well as resonances and have target strengths in excess of 0 dB with occasional schools exceeding 20‐dB target strength over a portion of the band. [Work supported by the Naval Material Command.]

Sound Propagation Studies of some Implosive Sources

A series of about 40 small (2-in. diam) inexpensive (approximately $70 per thousand) plastic spheres were sunk and thus imploded at sea near Westfall Seamount (30.5° N, 120.5° W). The implosive signals were monitored on both shallow (50-ft) and deep (1100-ft) hydrophones, suspended from the ship. Three types of spheres were tested and found to implode at 1800-, 2350-, and 2680-ft depths, respectively. Sink rates of 225–300 ft/min. were achieved using sections of pipe, or other hardware, as sinkers. Energy per unit area spectrum levels in the 0.5- to 5-kHz frequency band were, for one type of hydrosphere having an average implosion depth of 2680 ft, comparable to those for a 0.002-lb detonator (TNT). Use of such safe, inexpensive, and reliable implosive devices is recommended for acoustic work at sea when short pulses of relatively low signal strength are required.