Abstract

The utility of small-scale chemical explosion experiments in characterizing the seismic source is explored. An experiment using a 253 lb TNT charge detonated at a depth of 11.5 m was designed to address: (1) the importance of free surface interactions on the explosion source function; (2) the source characterization of chemical explosions; (3) the separation of isotropic and deviatoric source components; and (4) the utility of motion data from within the linear and nonlinear regime. The initial P pulse from the explosion grows from a rise time of 25 msec at 82 m/kt1/3 to 50 msec at 215 m/kt1/3. The corner frequency of the linear data (992 to 2976 m/kt1/3) is approximately 20 Hz. The interaction of the initially spherical wave front with the free surface results in spall. This nonlinear process redistributes energy into the 5-Hz band and appears as a spectral peak for ranges greater than 992 m/kt1/3. Transverse motions at ranges greater than 992 m/kt1/3 were 3 to 35 per cent of the radial and vertical accelerations. The radial and vertical motions changed little with azimuth supporting a cylindrically symmetric source.

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