A COMPARISON BETWEEN CONTROLLED-SOURCE AND PASSIVE SOURCE SEISMIC VELOCITY IMAGES

The unique access possible within a mine was utilized to detonate cont rolled 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 cont rolled sources were also used as simulated passive sources and inverte d for a velocity image, which was compared to the controlled source im age. Two passive source imaging techniques were used, a simultaneous v elocity inversion-hypocenter relocation method and an independent hypo center relocation and velocity inversion method. The simultaneous inve rsion method provided the best correlation between the controlled sour ce and simulated passive source images. Only slight improvement was fo und from multiple iterations of the simultaneous inversion, suggesting that the initial hypocenter estimate is sufficiently close to the ''t rue'' location for the problem to be essentially linear. The independe nt hypocenter relocation and velocity inversion method also provided a n image that correlated well with the controlled source image. Good co rrelation was also found in a comparison of the controlled source imag e with a passive source image calculated with mining-induced microeart hquakes. 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 .