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 the Morenci Copper Mine in Arizona. Its purpose was to design, detonate, record, and analyze seismic waveforms from these single-fired, contained explosions. Ground motion data from the SPE is analyzed in this study to assess the uniqueness of the source representation of these contained explosions and its ability to resolve 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 (Vp) are well constrained but the accompanying s-wave velocities (Vs) are less constrained. In order to assess the effects of source depth of burial (DOB) and Vs model on the seismic moment tensors, Green's functions (Gf) were computed for different DOB as well as different Vs models holding the Vp model constant. The Gf for the 16 near-source stations were calculated focusing on observations in the 37–680 m range. The compensated linear vector dipole and explosion components of the new Gf are compared to quantify the possible effects of DOB and Vs on the source representation. For the forward model, Gf with variable DOB and Vs 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 will guide new analysis of the observational data to understand the practical resolution of physical phenomenology accompanying underground explosion.

AAPG Datapages/Search and Discovery Article #90219 © 2015 GCAGS, Houston, Texas, September 20-22, 2015