Seismic Propagation from Activity in Tunnels and Underground Facilities

Dynamic mechanical activity in a tunnel can be measured as ground vibrations at offset distances. These signals can be processed in sensing algorithms for detection, location, and discrimination of the activity. The objective of this work is to demonstrate that seismic simulations can reveal the effect of the environment on seismic energy as it propagates from tunnels. Using massively parallel high-performance computers, the work applies a finite-difference solution to the equations of motion and isotropic stress-velocity for viscoelastic seismic propagation. Results from simulations in open, urban, and mountainous terrain reveal the nature of seismic waves as they propagate from tunnel-digging pulses and harmonic sources. Measures of relative energy and signal cross correlation provide maps that reveal locations of optimal sensing. We demonstrate applications of beam forming to monitor tunnel activity, and conclude that the simulation method produces realistic wave-field data for clarifying complicated propagation phenomena and for virtual trials of sensing algorithms.