Explosion Source Phenomenology

The explosion seismic source function is the potential which satisfies the spherical P-wave equation. It is completely de­ scribed by four properties. They are the steady-state value, roll-off, overshoot, and corner frequency. In one approach to describing the potential, the spectral roll-off is specified and the other properties are determined by fitting the data at prescribed times. In a variation of this approach, the roll-off is specified by assuming a radial stress of a known form is applied uniformly over a spherical surface, located at a range where the motion is assumed to be linear. In this review, it was found that of the four properties, less uncertainty exists about the steady-state value and the corner frequency than about the other two. A major problem has been scaling the results from one yield to another. New results are presented that show that, when the geo­ physical properties of the shot point are taken in account, cube-root scaling of the yield is appropriate for the steady-state value and the corner frequency, i.e., yield to the first and one-third powers, respec­ tively. The new results also suggest that previous assumptions about the form of the applied radial stress are probably not appropriate. Finally, chemical and nuclear explosions appear in the new results to be indistinguishable, suggesting that experiments using chemical explosions could aid in reducing the remaining uncertainty in the seismic source function properties.