A comparison between controlled source and passive source seismic velocity images

The unique access possible within a mine was utilized to detonate controlled explosions throughout the area monitored with a 3D underground seismic network. Measured P-wave travel times were inverted to compute a controlled source velocity image. The arrival times from these controlled sources were also used as simulated passive sources and inverted for a velocity image, which was compared to the controlled source image. Two passive source imaging techniques were used, a simultaneous velocity inversion-hypocenter relocation method and an independent hypocenter relocation and velocity inversion method. The simultaneous inversion method provided the best cor-relation between the controlled source and simulated passive source images. Only slight improvement was found from multiple iterations of the simultane-ous inversion, suggesting that the initial hypocenter estimate is sufficiently close to the "true " location for the problem to be essentially linear. The independent hypocenter relocation and velocity inversion method also pro-vided an image that correlated well with the controlled source image. Good correlation was also found in a comparison of the controlled source image with a passive source image calculated with mining-induced microearth-quakes. The correlation was improved with a combined inversion of the explosion and microearthquake data, suggesting that the discrepancies may be due to nonuniqueness of inversions of the individual data sets