Direct-SV Radiation Produced by Land Based P Sources Part 2 – Buried Explosives

A common view of buried-explosive seismic sources is that a buried explosion is a pure-P source because it is an expanding volume of high-pressure gas. This assumption leads to a popular conclusion that if shear-mode reflections are observed in explosive-source data, those reflections have to be produced by a downgoing SV wavefield that is generated by P-to-SV conversion at an interface above the depth of the buried explosive. An efficient interface where such P-to-SV mode conversion can occur is the earth-air interface. This paper challenges this traditional view that a buried chemical explosive is a pure-P source. In our finite-difference modeling, a buried explosion is a pure-P volume of expanding gas for only that fraction of a microsecond that it takes for its expanding gas to reach the wall of the tube that contains the explosive material. As soon as this accelerating high-pressure gas contacts any surrounding elastic media, a chemical explosion ceases to be a pure-P source, and shearing is initiate...