Understanding earthquake physics
Earthquakes are one of the most significant hazards for human society, and, at the same time, remain the most elusive. Improving the ability to forecast earthquakes is one of the main challenges remaining for the natural sciences. With the European Research Council (ERC) Synergy project “Fault Activation and Earthquake Rupture” (FEAR), a consortium of scientists from the Eidgenössiche Technische Hochschule Zürich (ETH Zurich) in Switzerland, the Rheinisch-Westfälische Hochschule (RWTH Aachen University) in Germany, and the Instituto Nazionale di Geofisica e Vulcanologia (INGV) in Italy are conducting a suite of ambitious experiments in the world-unique Bedretto Underground Laboratory for Geosciences and Geoenergy (BedrettoLab), an underground experimental facility in the Bedretto Tunnel, located at 1000m depth under the Swiss Alps.
The core idea of FEAR is to gain understanding on how earthquakes start and stop by using hydraulic stimulation to modify stress and initiate small non-damaging earthquakes (magnitude ~1.0 events on fault patches of 10-50m scale) on candidate faults in the vicinity of the Bedretto Tunnel. A dense network of multidisciplinary sensors will capture the rupture preparation phase, the earthquake rupture, and the post-rupture response of the rock mass. These experiments will give unprecedented up-close near-field insight into the physics of earthquake processes, contribute to pushing forward the current limits on earthquake predictability and advance the state-of-the-art in safe use of geoenergy.
FEAR-4 experiment successfully concluded
The FEAR-4 experiment was successfully concluded in the afternoon of 6 November, following approximately 50 hours of controlled water injection and continuous 24/7 monitoring between 4 and 6 November. The tunnel returned to normal operations on Monday, 9 November.
Injection operations began on 4 November at the BedrettoLab Earthquake Physics Testbed. Water was injected into two different boreholes from those used in the experiment conducted in September, with injection initially starting in one borehole and later expanding to the second borehole.
The experiment was stopped on Friday afternoon at 4:00 p.m., after a total of 550 m³ of water had been injected. More than 12,000 very small seismic events were induced, with local magnitudes ranging from −5 to −0.3. The boreholes will remain closed while microseismic activity continues to be monitored over the coming days.
FEAR-4 once again demonstrated that faults can be activated within the BedrettoLab Earthquake Physics Testbed and that the resulting seismicity remains within the expected range. Ground shaking measured outside the tunnel remained extremely low. Peak ground acceleration values recorded at the tunnel entrance, the Furka Base Tunnel and the Capanna Piansecco entrance ranged from 0.005 to 0.01 milli-g. These values are approximately 10,000 to 15,000 times below the design ground acceleration specified by Swiss standards, around 150 to 300 times below the threshold at which shaking can typically be felt, and approximately 1,500 to 3,000 times below levels associated with damaging earthquakes.
The team will now analyse the data and prepare for the next round of experiments in spring 2027. This will be preceded by a drilling campaign to place sensors close to the seismogenic areas identified during the FEAR-3 and FEAR-4 experiments.
Upcoming FEAR-4 experiment at the BedrettoLab
The BedrettoLab is preparing the next phase of the Fault Activation and Earthquake Rupture (FEAR) project. Building on the results of the FEAR-2 experiment conducted in April 2026 and the FEAR-3 experiment conducted in September 2026, researchers will carry out a new field experiment starting on 4 November 2026.
The FEAR project aims to improve our understanding of how earthquakes initiate and propagate by studying fault behaviour under carefully controlled conditions. One of the project's key scientific objectives is to trigger a controlled earthquake of approximately magnitude 1 within a natural fault zone located deep underground and directly accessible for experimentation and monitoring through BedrettoLab’s research infrastructure.
The previous FEAR-2 and FEAR-3 experiments provided valuable insights into the behaviour of the fault and confirmed the performance of the experimental infrastructure and monitoring systems. The upcoming experiment will build on these findings and further investigate the conditions under which controlled fault slip and earthquake rupture occur.
This time, water will be injected into the fault zone through two different boreholes than those used in the previous experiment, with injection initially starting in one borehole and later expanding to the second borehole. The injection is expected to last approximately 3 to 5 days. The experiment will be monitored continuously in real time from the BedrettoLab control centre at ETH Zürich.
A dense monitoring network consisting of sensors installed in and around the fault, including instruments measuring seismic activity, rock deformation, fluid pressure, temperature, and geochemical changes, will record the fault response throughout the experiment. These observations will help researchers better understand the physical processes that govern earthquake nucleation and fault activation.
The experiment has undergone a detailed safety and risk assessment, and multiple layers of safety measures are in place. All injection activities are remotely supervised, and no personnel are present in the BedrettoLab during the main injection phase.
Based on the safety and risk assessment, the seismic risk associated with the experiment is considered very low. Earthquakes generated during the experiment are not expected to be felt at the surface, in nearby buildings, or in the Furka Base Tunnel. The experiment will be conducted under strict operational limits and continuously monitored. If predefined safety thresholds are exceeded, injection operations will be stopped immediately.
Further updates and results will be published following completion of the experiment.
Find out more about our experiments here
FEAR annual meeting 2026 in Airolo
The annual FEAR meeting will take place from 19 to 21 May 2026 in Airolo.
FEAR annual meeting 2025 in Airolo
The annual meeting of the FEAR project took place from 13 to 15 May 2025 in Airolo and team members from Rome, Aachen and partners from Berkeley met. Participants reviewed the findings from several experiments already conducted, which provided a substantial basis for discussion. A key focus of the meeting was the upcoming completion of the new side tunnel and the associated experimental testbed where the FEAR main experiments will take place in approximately 6 months. As this marks a critical phase of the project, planning and coordination efforts were intensified.