Location of Mining Induced Seismicity in Zones of High P-Wave Velocity and in Zones of High P-Wave Velocity Gradient in Polish Mines

The passive tomography calculations have been made in Polish coal and copper mines for several years. To solve the passive tomography task the evolutionary optimization algorithm was chosen to search the minimum of the multidimensional function and the varying grid size of the velocity model was used. The main objective of tomographic calculations was to assess the seismic hazard. During the studies of tomographic velocity images the correlation between locations of seismic events and the zones of high velocity values was noticed. However, many cases of calculated tomographic velocity images have shown that seismic events were observed in the zones of high velocity gradient. Therefore one can conclude that seismic hazard zones should be combined not only with zones of high velocity values, but with zones of high velocity gradient values as well. In the paper a few velocity and velocity gradient images obtained from passive tomography calculations in Polish mines have been presented to confirm aforementioned relationships. The presented analysis of velocity and velocity gradient images indicates that passive tomography is helpful in seismic hazard assessment in Polish mines.