P and SV velocity waveforms from the Sterling explosion of December 3, 1966, are analyzed from a point of view often taken in earthquake source studies. The detonation occurred in the cavity excavated by the Salmon explosion within the Tatum salt dome, Mississippii, Velocity recordings taken from nearby borehole strong motion instruments show the occurrence of significant SV energy (Perret, 1968a, b). Kinematic source models are constructed by considering constraints afforded by the preshot cavity, condition of the surrounding material, and aspects of the P and SV waveforms such as wave polarity and duration. Waveforms for these models are computed and compared directly with the data. Modeling results suggest that the SV waves were radiated primarily by induced normal faulting occurring beneath the cavity rather than by an asymmetric pressure distribution based on the preshot cavity geometry. Secodary arrivals within the P waveforms and SV amplitudes suggest that these normal faults also had a component of tensional displacement which was probably due to forceable injection of material from the blast. A measurement for Qβ of 35 is obtained for salt from the amplitude decay and pulse width changes observed for SV waves along a profile taken at shot level. This value for Qβ is for the region away from the cracked area induced by the previous Salmon explosion and qualitatively explains the differing frequency content observed at the closest Sterling sensors between P and SV waves. The anomalous SV radiation has little to do with 'tectonic' stress release but is a result of the medium's geometry and anisotropy. |