Fault Activation and Earthquake Ruptures at the BedrettoLab

After more than 5 years of design, preparation and build-out, the Earthquake Physics Testbed at the Bedretto Underground Laboratory for Geosciences and Geoenergies ('BedrettoLab') is going into full operation in spring 2026. The testbed is being built for the Fault Activation and Earthquake Rupture (FEAR) project, around a carefully selected and heavily instrumented target fault zone at more than 1km depth. The fault is a steeply dipping, structurally immature fault and fracture zone, which, in the current stress field has oblique-normal faulting kinematics. To facilitate instrumentation, we have excavated a 110m long fault-parallel tunnel at a horizontal distance of 40 m from the fault. Using this access tunnel, we are densely instrumenting a volume of ca 100 x 100 x 200 m3 around the target fault zone, by placing over 200 sensors, of 25 different sensor types, and several hundred metres of fibre optics sensing cables, in over 40 boreholes.

Once completed, we will use multi-packer systems in 3 fault-crossing stimulation boreholes to re-activate the target fault with fluid injections. In a series of experiments we attempt to trigger dynamic ruptures with magnitudes of ~1.0, i.e. ruptures with fault dimensions of 10 - 100m. The goal is to resolve and study the micro-physical processes that govern fault preparation, earthquake nucleation, rupture dynamics and termination, as well as post-seismic processes, with a resolution and sensitivity that is not achievable for natural, tectonic earthquakes. In this talk we present the first results from the 'FEAR-2' experiment, the first experiment where we inject directly into the main segment of the target fault zone, and present the plans for more experiments in 2026 - 2027.