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Abstract:
The Fault Activation and Earthquake Rupture (FEAR) project aims at activating a natural granitic fault zone in the BedrettoLab at the 100m scale. The goal is to observe and study earthquake rupture phenomena in a natural setting from unusually close distance. The Bedretto Underground Laboratory for Geosciences and Geoenergies is a research laboratory in a 5km long tunnel in the southern Swiss Alps, with an overburden of up to 1.5km. At 2.4km into the Bedretto tunnel we have identified a ~2m thick natural fault zone. The fault zone consists of multiple distinct quartz and biotite shear fractures, some of which contain gauge layers of up to 5mm thickness. The fault zone is favourably oriented for rupture in the estimated present day background stress field. In autumn 2023, we plan to excavate a side tunnel that runs parallel to the fault zone for ~125m. This tunnel will facilitate the installation of a very dense multi-domain geophysical monitoring system, directly on and around to the fault zone. After a detailed characterization of the fault zone and the host rock, and with the monitoring system in place, we plan to activate the fault via water injection in multiple injection boreholes, in a suite of experiments. If successful, the experimental setup will allow us to study a wide range of seismic and aseismic crustal deformation phenomena from up close, including rupture preparation and precursory signals, rupture nucleation, coseismic strain localisation, rupture growth and termination as well as the post-seismic response of the fault zone.
