SUMMARY
When rock support is designed in a seismically active underground mine, it is important to know the ejection velocity to be able to calculate the corresponding kinetic energy. Field monitoring and back-analyses have shown that ejection velocities of the order of 10 m/s and higher can be caused by seismic events of moderate magnitude. This is much higher than the peak particle velocity (PPV) predicted by scaling laws. Many authors have related attenuation or amplification of the ground motion to the presence of discontinuities in the rock mass (Li et al., 2012; Zhao et al., 2006; Zhao et al., 2008; Potvin and Wesseloo, 2013; Cui et al., 2017). Velocity amplification of a P-wave travelling through fractured rock near a free surface was recently studied by Zhang et al. (2015). However, seismic events with large magnitude are often associated with slip along weaknesses or shear fracturing of intact rock, which according to observations radiate much stronger S-wave than P-waves. Thus, the amplification of S-waves in the skin of the excavation becomes more important. Zhao et al. (2006), studied the shear wave attenuation passing through a fractured rock mass far from a free surface. It was found that shear stress ratio (ratio of shear stress by shear strength) is the most important factor influencing wave propagation.

Svensk titel: EFFEKTER AV PARALLELA FRAKTURER NÄRA EN FRI YTA MED HASTIGHETSFÖRSTÄRKNING AV S-VÅG