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After extensive preparation—including drilling boreholes, installing sensors, and manufacturing a specially designed fault deformation probe—the experiment commenced in late November. Over three weeks, approximately 1’100 cubic metres of water were injected into the target fault zone via two boreholes, using a custom designed remote control system. This volume is roughly equivalent to 5’600 bathtubs of water. Importantly, all water used was sourced from wells in the tunnel, ensuring no drinking water was wasted.

The injection was expected to induce a response in the fault structure due to increased pressure in the surrounding rock. Initial analysis indicates minor fault movements, with detailed calculations underway to determine the extent of this displacement. Additionally, the experiment revealed greater complexity in the fault zone than previously assumed. During high-pressure injection, small seismic events occurred more than 50 meters away from the injection site, and suggest the presence of an extensive fracture network.

These findings confirm that the fault zone can be activated, and provide crucial information for the design of the next FEAR experiments, which will focus on the controlled activation of specific fault zone segments.