Source signature measurements of underwater explosives at very high ambient pressures

Abstract

The interpretation of seismic refraction experiments carried out on the deep-ocean floor has been hampered by lack of knowledge of the source signatures of explosives at these high ambient pressures. In order to fully exploit the data from such experiments, the source signatures of four explosives detonated at deep water depths have been measured. The explosives were commercially available Pentolite and three U.S. Navy explosives: PBXN-103, PBXN-111, and PBXW-127. A total of 75 ∼10 lb (4.54 kg) charges were detonated at depths of 2350–4593 m, and the source signatures were recorded at offset ranges of 160–230 m. For all four explosives, the period of the first oscillation follows the theoretically established relationship T=K*M1/3(Z+10)−5/6, where T is the period (s), M is the charge mass (kg), and Z is the detonation depth (m). The optimum value of K for Pentolite (2.07±0.01 s m5/6 kg−1) is identical to the value previously reported from the analysis of explosives detonated at depths of less than a few hundred meters. The optimum values for PBXN-103, PBXN-111, and PBXW-127 are 2.67±0.01 s m5/6 kg−1, 2.64±0.01 s m5/6 kg−1, and 2.73±0.01 s m5/6 kg−1, respectively. The greater bubble pulse period of the PBX-based explosives means that they are richer in low-frequency energy than Pentolite. The total energy flux in the frequency band 30–100 Hz is ∼6 dB greater for the PBX-based explosives than that for Pentolite at all detonation depths.