Accuracy of determining the power of underground nuclear explosions by a seismic method with known conditions of explosion

Abstract

The power* (TNT equivalent) of underground nuclear explosions is estimated by a seismic method from the magnitude calculated from the results of recording the seismic waves caused by the explosion. The magnitude of the longitudinal wave is related to the power Y (expressed in thousands of tons) by the regression equationwhere a and b are empirical coefficients.To take account of the influence of the medium, a dependence of the form in Eq. (i) is constructed, as a rule, for the three statistically most representative types of rock in which the explosion occurs: alluvium, tufa, and granite. This qualitative gradation of the typeso of rock characterizing their physicomechanical properties and correspondingly the different seismic effects is rough, does not reflect the whole diversity of actual rock conditions for explosions, and does not provide the necessary accuracy in estimating the power. In addition, the diversity of methods of measuring the signal parameters, the difference in the composition of the grids of seismic stations and the geography of their location relative to the tests sites, and the difference in the characteristics of the equipment employed and other factors (including subjective factors) means that there is a considerable spread in the values of a and b obtained by different researchers even for the same types of rocks and phases of the seismic signals; see [1][2][3][4][5][6][7][8][9], etc.At the same time, it is clear that the a priori value of the quantitative characteristics of the rock in which the explosion-occurs should facilitate an increase in the accuracy of estimation of their power. Therefore, in the case of explosions at declared test sites with a known geological structure and physicomechanical parameters of the rocks forming the test areas, conversion from a rough qualitative classification to a more complete and detailed quantitative representation must increase the accuracy. The following factors are taken into account here: the problem may be regarded as purely elastic for the teleseismic zone; a large quantity of random and determinate factors which cannot be taken quantitatively into account influence the relation between the seismic magnitude and the power of the explosion in real geological conditions. This often leads to the appearance of significant systematic shift in the dependences of the form in Eq. (i) on passing from one test region to another, which means that empirical dependences are preferred for monitoring specific test sites; many of the physicomechanical parameters of the rock determining the seismic effect of the explosion (density, elastic-wave velocity, porosity, moisture content, shear strength, etc.) are interrelated, or in any case correlate with one another, indicating that the number *In explosive seismology, the power of a nuclear explosion is usually taken to be its TNT equivalent, i.e., the mass of the TNT charge (in thousands of tons) which, on explosion, ~e-leases the same energy as the nuclear explosion (i000 ton is equivalent to i0 ~2 cal, 4.2"...