Intermediate period surface waves from mining explosions for crustal structure and source studies: Application in the western United States and northeast China (Wyoming, QianAn)

The study of intermediate period surface waves from mining explosions in Western USA (Wyoming) and Northeast China (QianAn) provides constraints on the crustal structure in these regions and the source mechanism of the explosions. Large-scale mining explosions as a result of their long time duration and large spatial extent can generate short- to intermediate-period (1--20 s) surface waves. Regional surface waves observed in the Western US were generated by four large-scale cast blasts in a Wyoming coal mine. Intermediate-period surface waves in Northeast China were generated by a mining explosion in an iron mine. Fundamental mode Rayleigh wave group velocities were estimated using multiple filter analysis and refined by phase matched filtering. Station specific velocity models were determined by linear inversion of the dispersion curves and found to complement known shallow crustal structure in each area.; Synthetics based on mining source models and the inverted velocity structure suggest that some combination of mine free face orientation, blasting direction and material casting contribute to the observations. The Wyoming and China studies are presented at Paper I and Paper II, respectively.; Assessment of surface wave dispersion provides the opportunity to make intermediate period Ms estimates with path correction. These surface wave magnitude estimates are combined with regional body wave magnitude estimates, mb, and compared to M s:mb data from explosions and earthquakes for purposes of identifying the source type. These results suggest that mining explosions are different from simultaneously detonated explosions and may appear earthquake like. This work is discussed in Paper III.; The surface wave inversions used in the first part of the study utilized common linearized inversion procedures. In order to assess the effect of the linearization, a niching genetic algorithm (NGA) was introduced, developed and tested for crustal shear-wave velocity inversion in Paper IV. This procedure maintains the ability to locate multiple solutions to the inversion problem. Application of this new technique to regional surface wave observations from the Powder River Basin illustrates the methodology and identifies multiple models that can then be checked for consistency with other geological and geophysical constraints.