Seismic Source Characterization of Small-Scale Contained Explosions Utilizing Near-Source Empirical Data

Abstract:

The Source Phenomenology Experiment (SPE) was a series of nine chemical explosions within a mine in Arizona. Its purpose was to collect seismic waveforms from these explosions for the purposes of resolving the equivalent elastic seismic source model. Ground motion data from the SPE are analyzed in this study to assess the uniqueness of the source representation of these contained explosions as well as the ability to resolve the trade-off between yield and depth when the geology or physical parameters of the source region may have a range of possible values. In this study, the p-wave velocities (V_p) are well constrained but the accompanying s-wave velocities (V_s) are less constrained. In order to assess the effects of source depth of burial (DOB) and V_s model on the seismic moment tensors, Green’s functions (G_f) were computed for different DOB as well as different V_s models holding the V_pmodel constant. The G_f for the 16, near-source stations were calculated focusing on observations in the 150-680 m range. The compensated linear vector dipole and explosion components of the new G_f are compared to quantify the possible effects of DOB and V_s on the source representation. G_f with variable DOB and V_s are convolved with the Mueller-Murphy isotropic source function to produce synthetic seismograms at a range of azimuths in order to assess tradeoffs. Noise is added to the synthetics to investigate their impact on the full recovery of the seismic moment tensor. Inversions, with real and synthetic data, are conducted where covariance matrices and condition numbers are formulated to evaluate the effects of station distance and azimuthal coverage on seismic moment tensor recovery. These procedures guide additional analysis of the observational data to quantify the practical resolution of physical phenomenology accompanying these contained explosion sources.