Status report on source properties important for discrimination

To begin, we need to discuss what is meant by source properties important for discrimination. Here we are concerned primarily with discriminating earthquakes from explosions by seismic means. We do not distinguish between chemical and nuclear explosions because, for concentrated explosions, these will appear identical except for a factor of two or so in the long-period amplitude (which will not be identifiable at a distant seismic station). Ripple-fired chemical explosions may, in theory, be distinguished from concentrated explosions by the spectral modulation that is produced by the former, however we specifically exclude spatio-temporal organization and other geometric effects and concentrate on material properties that have important influence on characteristics of the seismic signal which might allow explosions to be distinguished from earthquakes. The most prominent of these are the corner frequency of the seismic spectrum, the high-frequency roll-off, and the long-period overshoot. Both quasi-analytical{sup 1} methods and finite difference numerical solutions of the hydro-dynamic equations 1-6 were used to explore the effects of the: (1) equation of state of the explosion products; (2) equation of state of the rock media surrounding the explosion; (3) energy and mass density of the explosion source; (4) constitutive properties of the surrounding rock media, including: (a) compressive and tensile strength; (b) porosity; (c) dilatancy; and (d) elastic moduli; and (5) depth of burial (lithostatic overburden). The calculations performed thus far assumed one-dimensional radial symmetry for the most part so that, in addition to geometric details of the source excluded from consideration, depth effects on spall are excluded as well. For our analysis we have chosen models that offer a wide range of parametric behavior and also that have generally given good agreement with experiment