Ground motions induced by mining seismic events with different focal mechanisms

Abstract

It is essential to quantify the ground motions induced by seismic events with different focal mechanisms in underground mine. To quantitatively calculate the induced ground motions, we expressed the motions as the convolution of the seismic source and the wave propagation path using seismological method. Firstly, we investigated the theoretical ground motion patterns using four idealized focal mechanisms. Results show that the pure compressional failure source and the pure tensional failure source induced the same ground motion patterns. The vibrations they induced attenuate extremely fast. The pure shear failure source shows closely azimuth related pattern with four quadrants around the source. The pure explosive failure source induces vibrations attenuating toward all directions away from the source. But the vibrations are not attenuated gradually with the increasing distance. Then, we investigated the ground motions under complicated focal mechanisms using recorded fault slip events, cavity collapse events, and tensional failure events. The fault slip events show a four quadrants ground motion distribution in the horizontal plane and a two quadrants distribution in the vertical plan. But the cavity collapse events show a two quadrants distribution in the horizontal plane and a four quadrants distribution in the vertical plane. It is concluded that the induced ground motion at a certain location is controlled by the dual effects of the azimuth and the source focal mechanism as well as the distance and the source magnitude.