High-resolution mini-seismic methods applied in the Mont Terri rock laboratory (Switzerland)

We present several mini-seismic methods developed and applied in recent years in the Mont Terri rock laboratory. All these applications aimed at correlating and interpreting seismically derived parameters with relevant rock-mechanical parameters and findings. The complexity of the local site setting always required very high spatial and parameter resolution. Both, seismic P- and S-wave velocities and dynamic elastic parameters, such as the dynamic Poisson’s ratio υdyn and the Young’s modulus Edyn, are used to characterise the Opalinus Clay under real in situ conditions. We were able to establish a correlation between static and dynamic elastic Young’s moduli. We describe the extremely large, small-scale variability of seismic parameters normal and parallel to the bedding plane orientation and address the question of fracture detection. We also present examples of the characterization of excavation-damaged zones with seismic parameters, including extent as well as degree of damage, and compare these to geological and structural mapping. The evolution of borehole-disturbed zones (BdZ) was deduced from repeating high-resolution borehole measurements. Finally, we quantify seismic anisotropy at dimensions between several cm and tens of m.