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.

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.

Injection operations began on 21 September at the BedrettoLab Earthquake Physics Testbed. Water was injected into two boreholes using a set of pumps. In contrast to the experiment conducted in April, the team tested a different operational approach by applying high injection flow rates from the start. 

At 6:30 a.m. on 23 September, a seismic event with a local magnitude of 0.6 was triggered. Following this event, and after a total of approximately 590 m³ of water had been injected and almost 7000 events with magnitude down to –4.7 were recorded, the team decided to conclude the experiment and stop the injection. The boreholes will remain closed while microseismic activity continues to be monitored over the coming days. 

The experiment once again demonstrated that faults can be activated within the BedrettoLab Earthquake Physics Testbed and that the resulting seismicity remains within the expected range. In FEAR 3, the maximum magnitude produced in the BedrettoLab to date increased by one order of magnitude, as planned. 

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 0.03 to 0.27 milli-g. These values are approximately 2,000 to 3,000 times below the design ground acceleration specified by Swiss standards, around 150 times below the threshold at which shaking can typically be felt, and approximately 1,500 times below levels associated with damaging earthquakes. 

The team will now analyse the data and prepare for the next round of experiments. This will be preceded by a drilling campaign to place sensors close to the seismogenic areas identified during this FEAR 3 experiment. 

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 experiment 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.

During the experiment, water will be injected into the fault zone through two boreholes. The injection is expected to last approximately 3 to 5 days. This time, however, we plan to reach high pressures quite rapidly, as fast as technically possible. 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.

This experiment was our first attempt to induce a magnitude 1.0 earthquake in the Earthquake Physics Testbed at BedrettoLab. A magnitude 1.0 event is very small and cannot be felt, but it is an important scientific target. By observing earthquakes of this size under controlled conditions, we can better understand how earthquakes start, grow and stop. Using controlled high‑pressure fluid injections, we were able to activate a specific fault zone and set the surrounding rock in motion.
We recorded more than 12,000 very small earthquakes (“microquakes”) within the experimental area. These events had magnitudes between −5 and −0.1, meaning the target magnitude of 1.0 was not yet reached. The injections were stopped because the activity began to move away from the most densely monitored zone. Despite this, the experiment produced an exceptionally rich dataset that helps us better understand how faults are activated.
A key part of the experiment is our advanced monitoring system. It allows us to measure seismic waves across a wide range of frequencies and amplitudes, as well as other important physical parameters. One important component is a network of fibre‑optic cables installed in boreholes and along the tunnel floor. Using a technique called Distributed Acoustic Sensing (DAS), these cables can detect both ground shaking and very small permanent deformations caused by earthquakes. Such deformations are well known in large natural earthquakes but are rarely measurable in small events.
In addition, a specially designed digital control system allowed us to run and monitor the entire experiment remotely from Zurich. This system is a key part of our safety concept and performed reliably throughout the experiment. For example, during an unexpected electrical short circuit, the system immediately shut down the experiment as designed, preventing further damage and demonstrating the effectiveness of the safety concept.
Although the detailed analysis is still ongoing, the potential of our monitoring system is already clear. For example, the recorded data (see animation) provides a detailed view of how and where the fault was activated.
Based on these results, we are now preparing a series of follow‑up experiments. The goal is to gradually increase the maximum magnitude towards 1.0. These experiments will allow us to observe earthquake processes with unprecedented detail and represent an important step towards controlled earthquake experiments beyond BedrettoLab.

Injection operations started on Wednesday afternoon, 22 April. During the following night, the experiment was temporarily interrupted due to an unexpected  power outage. After repair work was completed, injection was resumed on Thursday, 23 April in the late afternoon. The simultaneous injections via two stimulation intervals in two separate boreholes led to the activation of several structures across the heavily instrumented experimental volume.

The experiment was stopped on Saturday morning at 08:30, after a total of 750 m³ of water had been injected over approximately 50 hours of pump operation. very small seismic events were induced, with local magnitudes ranging from −5 to −0.14. While some seismic events occurred on the target fault zone, a large number of events took place on neighbouring geological structures activated by the fluid injection. The decision to stop the experiment was taken when an increasing number of seismic events occurred outside of the core measurement network, limiting their scientific analysis.

Overall, the experiment confirmed that faults can be activated at the BedrettoLabs' Earthquake Physics Testbed, and that resulting seismicity remains within the expected range. The ground shaking produced outside the tunnel was 5’000 to 6’000 times below the design ground acceleration value from the Swiss Norms, with peak ground acceleration values of 0.000014g at the tunnel entrance, 0.0000167g at the top of the mountain, and 0.0000172g at the Furka Base Tunnel entrance. These values are approximately 700 times below the level associated with perceptible and approximately 7’000 times below levels associated with damaging earthquakes.

The research team has begun a first analysis of the collected data, which will inform the preparation of the next FEAR 2 experiment planned for June or September.

To carry out this work, the team has built a new 120 metre long tunnel starting 2.2 km from the entrance of the main Bedretto tunnel, providing direct access to the fault. A dense monitoring network consisting of several types of sensors placed on and around the fault, in over 40 boreholes, will measure rock deformation, fluid pressure, temperature, seismic activity, and biochemical changes. These observations will help scientists study the entire sequence of processes leading up to and following an earthquake. 

The FEAR-2 experiment has been preceded by hydromechanical tests to understand how fluid injection affects the fault’s pressure conditions, deformation, and stability, and how these coupled processes may influence seismic activity. 

The subsequent main experiment, hydraulic stimulation, will consist of water being injected over a period of several days to weeks. This process will operate around the clock and be monitored in real time. The team will start by injecting at low pressure, gradually increasing it until the target magnitude of 1 is reached or until 2000 m³ of water has been injected. Numerous much smaller earthquakes are expected to occur before the target magnitude is achieved. 

The experiment has undergone a detailed safety and risk assessment, and several layers of safety measures are in place. All high-pressure injection activities are controlled remotely from Zurich, which means that no personnel are present in the tunnel during the stimulations. 

According to the safety and risk assessment, the targeted magnitude 1.0 event would likely cause no damage, although very minor damage to the Bedretto and FEAR tunnels, located 30 to 50 meters from the rupture plane, is possible. Severe damage to the tunnels would only be expected in the case of a significantly larger event, with a magnitude of 2.5 or greater. The probability of such an event is estimated at around 1 percent. 

We do not expect earthquakes related to the FEAR-2 experiment to be felt or to cause any damage at the surface, in the Furka Base tunnel (2 to 2.5 kilometres away), or in nearby buildings. The probability of an earthquake causing damage outside the Bedretto tunnel is about 0.01 percent (1 in 10,000) and is therefore extremely low. It is much lower than the probability that a natural earthquake occurring over the same period would be felt or cause damage in the area. 

Overall, the analysis shows that the FEAR-2 experiments can be carried out safely, with a very low and acceptable level of seismic risk for the Bedretto tunnel, the Furka Base Tunnel, and nearby buildings. The experiment will be closely monitored at all times and will follow strict safety procedures. If any safety threshold is exceeded, injection will be stopped immediately. 

ETH Zurich has constructed a 120-meter-long side tunnel at the BedrettoLab, an underground research facility in Ticino (Switzerland). This new tunnel runs parallel to a carefully selected natural fault zone. Thanks to this specific location, researchers can study in detail how an earthquake starts at one point along a fault and then propagates until it runs out of energy. Using specialized equipment, an European research consortium is studying how faults move to better understand – and potentially predict – earthquakes. The project behind this initiative, called Fault Activation and Earthquake Rupture (FEAR), was funded by the European Research Council with €14 million. It aims to answer two of the most fundamental and unresolved questions in seismology: What happens just before an earthquake begins, and what causes it to stop. Researchers hope that answering these questions will help push the boundaries of earthquake predictability.

A unique on-fault observatory

To study earthquakes right at their source, the FEAR team drilled numerous boreholes. Most of them to monitor processes in the rock. Others to inject water and induce small earthquakes. They are equipped with a wide range of sensors and together form a novel on-fault monitoring network. The sensors are sensitive enough to detect earthquakes as small as magnitude -5 and will also measure other parameters such as fluid pressure in fractures, stress changes, and more. During the large-scale stimulation experiments the team is now preparing, hundreds of cubic meters of water are injected into the fault zone at high pressure. Fluid overpressure reduces the existing stress on fault planes, weakening them and making it easier for them to slip. This reduction in friction can trigger fault movement, resulting in induced earthquakes.

“An on-fault observatory is the missing piece of the puzzle in studying earthquakes”, says Prof. Domenico Giardini, one of the four principal investigators of the FEAR project. “We have excellent monitoring networks around the world. However, most are placed on the surface and are therefore located several kilometers away from the earthquake's point of origin. And even the few sensors placed in boreholes are usually only near fault zones, not directly within them.”

Triggering a magnitude 1 earthquake

In their upcoming experiments, the research team intends to induce a magnitude 1 earthquake. That is typically well below the threshold of human perception, which is around magnitude 2.5 at the surface. However, within meters of a fault, the resulting ground motions can be strong. The FEAR researchers build on extensive experience from the past 4 years, having conducted numerous injection experiments in the BedrettoLab, with increasing levels of injection pressure, and so far triggering earthquakes up to a magnitude of -0.5. The dense network of sensors, placed both on and around the target fault zone, will help the researchers understand what happens before, during, and after such an event. The researchers will also look for diagnostic precursory signals, which may not be detectable with less sensitive monitoring setups, and which could one day help predict large earthquakes.