Nonlinear mesoscopic elasticity revealed by passive seismic monitoring of a rock column during drilling operations

We report the repeated in situ observation of nonlinear mesoscopic elasticity in an ∼760 m3 unstable rock column undergoing drilling for bolting reinforcement. Analysis of the anomalous nonlinear fast dynamics at the onset of drilling showed a clear correlation between top-of-column acceleration and small (a few percent) drops in resonance frequency. Slow dynamics were also observed, appearing as reproducible recovery of the fundamental resonance frequency after both drilling stopped and earthqu