News Archive - 2024

Using an ultra-high frequency seismic network, the researchers detected seismic events as small as Mw < −4, revealing a complex fracture network extending over 100 meters from the injection sites. The analysis shows significant variability in the affected rock volume, ranging from a few meters to over 150 meters, and identifies multiple reactivated fractures. Seismic events typically propagate upward along planes aligned with the stress field and pre-existing fractures. The results highlight the diversity in seismic behavior, which is not solely dependent on the injection protocol, and confirm that multi-stage stimulations with zonal isolation can create a large, 3D fracture network essential for enhanced geothermal systems. The findings also offer insights into upscaling induced seismicity from laboratory to field scale.

Link to paper:

Obermann, A., Rosskopf, M., Durand, V., Plenkers, K., Bröker, K., Rinaldi, A. P., et al. (2024). Seismic response of hectometer-scale fracture systems to hydraulic stimulation in the Bedretto underground laboratory, Switzerland. Journal of Geophysical Research: Solid Earth, 129, e2024JB029836. https://doi.org/10.1029/2024JB029836

A deeper understanding of earthquakes

The upcoming experiment is dedicated to characterizing the target fault in the BedrettoLab, which crosses the FEAR testbed. This testbed is currently under development, including the excavation of a new side tunnel. Decisive for this upcoming experiment is a newly developed measuring probe (developed by Lawrence Berkeley National Laboratory LBNL) which will be used in two experimental boreholes to measure pressure changes and fault deformations directly on the target fault. With this probe slow fault deformation can be measured with high sensitivity and accuracy. This allows to study how earthquakes begin, and how fluid injections can increase the fault zone permeability.

Safety concept

To ensure a safe procedure, as for every BedrettoLab experiment, a stringent and conservative safety concept is being followed. The experiment control and monitoring systems are operated remotely, so that nobody is in the tunnel during high pressure injection phases. During injections, a team of seismologists and engineers is monitoring the experiment around the clock. Additionally, a Traffic Light System ensures that the experiment is stopped if predefined magnitude or ground shaking thresholds are exceeded. Further large-scale experiments in the framework of the FEAR project are planned for 2025.

The construction company, Consorzio Cristallina, started in June 2024 with a phase of drill-and-blast followed by a soft excavation phase. Both excavation methods and their influences on the surrounding rock are studied within the Precode project, lead by RWTH Aachen.
The FEAR project will now enter a first experimental phase starting in mid-November. From January 2025 on, we will continue with the side-tunnel expansion, involving 100 meters of drill-and-blast excavation. The FEAR tunnel is expected to be fully completed by summer 2025.

As anticipated, the injection triggered a high level of microseismicity: our real-time monitoring workflow detected several thousand tiny earthquakes. The two largest events reached a magnitude of around -1.0. This is equivalent to when rocks rupture in an area of one meter in diameter and move by up to 1 millimetre.
The experiment was conducted according to a previously designed protocol. With the new remote-control system, the entire experiment and monitoring could be conducted from a control room at ETH Zurich and the Barracke near the tunnel entrance in Ronco, with no one in the tunnel.
Now, the team is busy analysing the rich data set and preparing for the next experiments in November and December 2024.

This approach will help determine if the seismicity characteristics remain consistent with or differ from the prior experiment, which involved several days of rock mass preconditioning at intermediate pressures (15 MPa). 

The potential risks associated with these experiments are considered low. However, safety measures have been implemented, including remote-controlled pump circuits that allow the experiments to be conducted without personnel in the tunnel. Additionally, predefined thresholds for magnitude and ground motion will trigger the halt of the injection to avoid any dangerous ground motions to occur. 

Two real-time monitoring systems, based on the SeisComP framework, monitor both background seismicity and injection experiments, utilizing a range of sensors with varying sampling rates. The standardized workflow for data processing includes automatic picking, phase association, magnitude estimation, double-difference relocation, and waveform cross-correlation, facilitating novel methods in seismology.

Link to paper:

Maria Mesimeri, Luca Scarabello, Eric Zimmermann, Thomas Haag, Emil Zylis, Linus Villiger, Philipp Kaestli, Men-Andrin Meier, Antonio Pio Rinaldi, Anne Obermann, Marian Hertrich, John Clinton, Domenico Giardini, Stefan Wiemer; Multiscale Seismic Monitoring in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG). Seismological Research Letters 2024; doi: https://doi.org/10.1785/0220240128

The granite features four main classes of deformation structures, indicating a sequence of brittle and ductile shear zones. These findings are crucial for ongoing and future projects at BedrettoLab, as they show that the structural framework of the Rotondo granite is primarily defined by old brittle faults and fractures, rather than just ductile shear zones. Understanding this complex deformation history provides important insights for our research and projects targeting fault zone reactivation.

Link to paper:

Ceccato, A., Behr, W. M., Zappone, A. S., Tavazzani, L., & Giuliani, A. (2024). Structural evolution, exhumation rates, and rheology of the European crust during Alpine collision: Constraints from the Rotondo granite—Gotthard nappe. Tectonics, 43, e2023TC008219. https://doi.org/10.1029/2023TC008219

Up to now there have only been occasional opportunities for the public to visit this unique research infrastructure. However, that is about to change thanks to a partnership with the nearby Sasso San Gottardo Museum, meaning that members of the public can tour the BedrettoLab on the following dates this year:

• Saturday 20 July 2024
• Saturday 3 August 2024
• Saturday 28 September 2024
• tours start at each date: 11 a.m., 12 a.m., 2 p.m., 3 p.m.

On each of these days we will be offering four guided tours in German and four in Italian. Those interested in taking part can check the time slots for each language online. Tours can be booked now on the Sasso San Gottardo Museum's website (www.sasso-sangottardo.ch/bedrettolab) at a price of CHF 25 per person.

What does a tour involve?

It will consist of a walking tour lasting around two hours and covering a distance of about 4.5 kilometres. This means that it is only suitable for individuals who will have no trouble navigating their way across uneven terrain for this length of time. Geology and research are brought together in the BedrettoLab: the Sasso San Gottardo Museum's guides will lead visitors through the unclad rock tunnel holding the BedrettoLab, while pointing out and explaining various geological phenomena that would be difficult to spot otherwise. Visitors can also take in the BedrettoLab's geothermal test environment, giving them an insight into the ongoing research work at ETH Zurich.

Direct link for ticket sales: www.sasso-sangottardo.ch/bedrettolab

More information about the guided tours is available here: www.bedrettolab.ethz.ch/en/about/visit

Alle Infos auf Deutsch: www.bedrettolab.ethz.ch/en/about/visit/public-visits-info-DE/

Furthermore, his analyses of the hydraulic stimulation experiments suggest hydraulic shearing of pre-existing fractures as a probable reactivation mechanism. The pressure and flow rate datasets and their interpretation will help in the future integration and interpretation of monitoring data for seismicity, strain and pressure as well as in the improvement of numerical models for hydraulic stimulations.

For his doctoral thesis, Kai drew on a wealth of experience that he gained in the BedrettoLab, where he already completed his Master's thesis on “In-situ stress and rock mass characterisation via mini-frac tests at the Bedretto Underground Laboratory”. In addition to his excellent scientific work, Kai has been involved in setting up and developing the BedrettoLab from the very beginning. We, the entire BedrettoLab team congratulate him on his completed doctoral thesis and are happy that he is continuing his work in the BedrettoLab as a postdoctoral researcher at the Center for Hydrogeology and Geothermics at the Université de Neuchâtel.

For more insights, access here the doctoral thesis of Kai with the titel “From stress field heterogeneity to hydraulic stimulation mechanisms: Insights from a hectometer-scale fractured rock mass”.

In an earthquake of this magnitude, the rock moves along a plane by about 1-2 millimeters over an area of roughly 5-by-5 meters. This rupture lasts only a millisecond and radiates seismic waves, which our sensitive monitoring arrays are designed to capture. The waves are much too weak to be felt at the surface.
The seismology team uses these detailed recordings of such a small event to study the physical processes that occur during an earthquake. A better understanding of such processes may lead to improvements in earthquake risk mitigation and management in the future. It also contributes to better management of induced seismicity related to deep geothermal energy projects. Currently, the team is analyzing and modeling the collected data, and preparing the next long-term injection scheduled for autumn.

In past experiments, the largest observed micro-earthquake was about a magnitude -2; in the upcoming M0 experiment, the team strives to reach about a magnitude 0. Such an event is about 100 times larger in amplitude and releases about 1´000 times more energy than a magnitude -2. Such an event would rupture a patch of about two by two meters by about one centimetre, allowing us to study when and where such a micro-earthquake starts, how it ruptures, and when it stops. For comparison, a natural earthquake of magnitude 6 that occurs in Switzerland every 50 to 150 years ruptures a patch of 10 by 10 kilometres by one meter, releasing about 1 billion times more energy.

Magnitude 0 events have already occurred naturally in the vicinity of the tunnel, and such micro-earthquakes remain about 100 to 1’000 times too small to be felt by people in the Bedretto Valley at a distance of several kilometres. The likelihood of induced larger events that could be detected in the Bedretto Valley remains extremely low. However, even micro-earthquakes of magnitude zero to one can be felt if experienced within a few meters or tens of meters of them. To eliminate even the smallest risk to people in the tunnel, these experiments will not only be very closely monitored, but they will also for the first time be fully remote controlled. During the main injection, no people will be allowed in the tunnel. This remote-control capability will be even more important later in the FEAR project when patches of 10 meters are the target size. 

During the main part of the experiment, about twenty dedicated members of the BedrettoLab team will be working in 24/7 shifts over a period of one week. Their primary task will be to monitor the pressure, flow rate, deformation, and seismicity behaviour in real-time. The geobiological and geochemical response of the reservoir will also be closely monitored, for example, to detect pre-cursors before larger ruptures. As implemented for previous experiments, two traffic light systems regulate the experiment, and if the observed vibrations or magnitude exceed pre-defined thresholds, the experiment will be ended immediately and bleed-off initiated; past experiments have shown that seismicity will then within minutes to hours decrease strongly.

The project consortium consists of scientists from the BedrettoLab, the Geothermal Energy and Geofluids group at ETH Zurich, researchers from SUPSI, and industry experts from Azienda Elettrica Ticinese (AET) as well as Geo-Energie Suisse (GES).

BEACH will play a key role in tackling the challenges of the Swiss energy transition by demonstrating a new technology for storing and retrieving energy in the subsurface. With the energy grid shifting towards renewable energies such as wind or solar energy, seasonal phases of energy demand surplus demand for an efficient and sustainable solution for energy storage. While thermal energy storage in soft sediments (e.g. in the Netherlands) is well established, storing heat in the hard, fractured rock most common in Switzerland remains largely unexplored.  The BEACH project will explore a so-called fractured thermal energy storage in the limited permeability of the crystalline rocks in the BedrettoLab.

For demonstrating the feasibility, warm water (30 - 70 °C) will be injected into existing fractures, where it will be stored and kept warm by the surrounding rock until it will be retrieved again. In a real-world roll-out scenario, the heat could then be converted into energy or used for district heating.

The tests are accompanied by comprehensive real-time-monitoring and numerical simulations for optimizing the geothermal energy system. Ultimately, the technology will be proposed on a cantonal and national level for real-scale sites to be realized by industrial partners as an additional part of the project. A real-scale reservoir in crystalline rock could be established close to infrastructures with high energy excess and/or demand, such as industrial areas, at depths of around 1 to 3 kilometers.

Maren Brehme from ETH Zurich leads the BEACH project awarded with a fund of 2.96 Mio CHF. The community of Bedretto and the canton of Ticino support the project in rolling out the technology on a national level.

What is your research in the BedrettoLab about?

My research journey in the BedrettoLab started in 2020. In general, in my field, to get access to “deep ecosystems” is not easy. So, to have the BedrettoLab in such close distance and with almost permanent access is a big opportunity. At the beginning, we just wanted to find out what is there, in the boreholes and in the water that flows through the various fractures. We began to take many water samples to get an idea of the sampled water, where it originates from and what the chemistry looks like. Our aim is to identify energy sources in the water or on the rock surface that can feed microorganisms. Such energy sources include for example CO₂ or nitrogen, which can be found in different amounts throughout the tunnel.

Once we got a better idea of what is existing, we also started to examine the effects of hydraulic stimulations on the microbiome, a term for the microogranisms that exist in a particular environment. We observed changes in the water chemistry and microbial populations during stimulations. Now, we maintain a geobiological monitoring borehole and “observe” the water chemistry and biology on a long-term basis with different permanent measuring installations. In this borehole we perform various experiments to better understand how the microorganisms in the BedrettoLab survive and evolve.

We have also installed additional monitoring stations to see if there are seasonal or experimental-associated changes in the system. We called the entire setup “DELOS” which stands for “Deep Life Observatory”, a tribute to the Greek island that shares the same name and prohibited dying. The microorganisms living in Bedretto’s DELOS have refused to die, even though they are hundreds to thousands of meters away from the sun and the surface.

What tools and methods do you use?

My team usually turns up in the tunnel with buckets and lots of bottles. With those vessels, we take our water samples directly from the boreholes or from a water source somewhere in the tunnel. Then we take the samples to our laboratory here at ETH Zurich and analyze them. This means that we look at water drops under the microscope, we do chemical analyzes or, if we identify interesting microorganisms, we try to cultivate them and do DNA sequencing. As we collect lots of data about the DELOS ecosystem as a whole, we also use machine learning to combine these data with the DNA analyses. Machine learning algorithms help us to identify patterns and ultimately connections between the environment or changes in it that lead to changes in the microorganisms, e.g. bacteria, and the occurrences of certain life forms.

Did you discover anything surprising during your research in the BedrettoLab?

We have found a large population of a set of extremely interesting ultra-small bacteria. They have extremely small genomes compared to complex life-forms such as plants and are among the smallest life-forms on earth. So, we are wondering, why exactly those bacteria do occur here, what do they need to survive and where are they originating from.

During the hydraulic stimulations we have also discovered a change in the water chemistry that is quite likely coming from the new fractures created in the rock. This means, when the rock breaks, a reaction is set in motion in which water molecules are split and hydrogen and oxygen is set free. What comes out is a highly reactive liquid that offers energy for potential life. We are wondering, if this was maybe an energy source for early life.

With your “Center for Origin and Prevalence of Life” you also open your eyes to other planets and the possibility of extraterrestrial life. What does your research have to do with life on other planets?

The reaction that I described earlier, where silicate rock, like the Rotondo granite and water react to produce bio-chemical energy, is quite generic. This means that it could also occur in the subsurface of other planets and power alternative ecosystems. This reaction pathway makes the existence of extra-terrestrial life more likely for example on Mars.