On the seismic source function of an underwater explosion

SUMMARYThe seismic source function of an underwater explosion (UWE) is studied based on characteristics of the shock wave and the secondary bubble pulses. A mathematic representation for the full pressure history including overpressure and underpressure caused by both shock wave and bubble pulses is presented. Based on the full pressure model, UWEs’ reduced displacement/velocity potentials both in time and frequency domain are obtained. The new seismic source model overcomes the theoretical inconsistency with the UWE seismic source model presented by Savage & Helmberger taking account of the shock wave overpressure only, and the steady-state reduced displacement potential predicted by the full pressure model is much larger than that predicted by the shock wave model by a factor that would exceed 100 for shallow UWEs. Relative seismic effect between underwater and underground explosions is modelled and the result by the full pressure model is consistent with observations that seismic magnitude of an UWE commonly is much larger than magnitude of an underground explosion of the same yield. And to further validate the full pressure model, Pn spectra of a 10 000lbs UWE off the east coast of Florida detonated on 2016 June 10 are modelled for six regional stations, and the results predicted by the full pressure model agree well with corresponding observations.