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.
The 3rd FEAR Annual Meeting was held in in Rome from 29-31 March 2023. The team of more than 50 participants, from the three beneficiary institutions - ETH Zurich, INGV Rome, RWTH Aachen - as well as members of the external advisory board and external collaborators, gathered to share their progress and discuss the next steps of the project, in particular, the details of the upcoming FEAR Experiment 1, scheduled to be conducted in October 2023.
The major developments since the last meeting included the selection of the MC fault as the target fault zone, the extensive characterization/prospection campaign centered around the MC fault, and the decision to drill the FEAR tunnel to the right of the Bedretto tunnel, with Experiments 2,3, and 4 taking place to the right, and locating Experiment 1 to the left of the Bedretto tunnel to minimize the probability of triggering the magnitude 1 FEAR main shock before the full monitoring system is in place. In addition, numerical models are being developed to investigate how to trigger ruptures on a nominally strengthening fault. The detailed design of the multidisciplinary FEAR monitoring system, which will collect observations from fault processes at unusually close distances, is being further refined.
The breakout sessions of the meeting were focused on how to characterize and model the target MC fault zone and how to instrument and activate the MC fault zone for FEAR Experiment 1. Members of the external advisory board provided valuable feedback and insight. The poster sessions provided opportunities for researchers to have more in-depth discussions and get feedback on specific details of their work.
In keeping with tradition, the program included some fun and entertainment to balance out the full and intense days. Stewardship certificates for the 15 boreholes drilled in the last year were distributed. The FEAR band performed during an apero on the hotel rooftoop, with a beautiful spring evening in Rome as the background. At the end of the meeting, a geology-seismology walking tour took the participants through Rome, highlighting how geology drove the development of the city and showing signatures of past seismicity on ancient buildings.
The drilling campaign for additional FEAR boreholes started last week. In the next two weeks, eight boreholes with lengths of 9 to 12 meters each will be drilled. They are designed for the placement of highly sensitive acoustic emission sensors which will be part of the initial phase of the FEAR Integrated Monitoring System (FIMoS). The full FIMoS, which will be built in phases, will be a large array of multi-disciplinary sensors installed in boreholes drilled from the to-be-constructed FEAR side tunnel and near the target rupture planes. FIMoS is designed to monitor, record, and image faulting processes at very close distances with high precision. We expect to record more than 100’000 micro-earthquakes in the magnitude range -4 to 2 throughout the duration of the FEAR project.