Forward and Inverse Modeling of Near-Field Seismic Waveforms from Underground Nuclear Explosions for Effective Source Functions and Structure Parameters

摘要

It is well established that near fields records of nuclear explosions can be analyzed to obtain detailed information about the seismic source function and its dependence on yield. This information is generally formulated in terms of parametrized models for the RDP and for the test site crustal structure. In this study, we review the results of forward modeling studies to obtain the source and structure parameters for Pahute Mesa. These models fit the observed near field records well, but there is some question as to how errors in crustal structure might affect seismic source parameters. Furthermore, there is a general need to be able to develop source-structure models in a consistent, unbiased fashion. To address these issues, we have developed a simultaneous inversion for source and structure parameters. In previous reports, we discussed the development of the method and applied it to Pahute Mesa data. In this report, we present an application of an improved technique for inverting for parameters in these types of problems known as the jumping method. A second problem with analysis of near-field records from explosions is that there is some question as to whether crustal materials respond in a linear anelastic or anelastic fashion or whether they have significant nonlinear response because of the high shear strain levels. Near-field data sets from several nuclear explosions and an earthquake are examined to address this question. It is shown that if nonlinear material response occurs it does not have a large enough effect to have a significant effect on data interpretation.