Comment on egusphere-2024-586

Abstract

Abstract. Performing stimulation experiments at approximately 1 km depth in the Bedretto Underground Laboratory for Geosciences and Geoenergies necessitates identifying and characterizing the target fault zone for on-fault monitoring of induced fault-slip and seismicity, a current challenge in understanding seismogenic processes. We discuss the multidisciplinary approach for selecting the target fault zone for the experiments planned within the Fault Activation and Earthquake Ruptures (FEAR) project, aiming to induce fault-slip and seismicity up to a magnitude 1.0 earthquake while enhancing monitoring and control of fluid-injection experiments. Structural geological mapping, remote sensing, exploration drilling and borehole logging, ground-penetration radar, and laboratory investigations were employed to identify and characterize the target fault – a ductile-brittle shear zone several meters wide with intensely fractured volume persisting over 100 m. Its orientation in the in-situ stress field favors reactivation in normal to strike-slip regimes. Laboratory tests showed slight velocity strengthening of the fault gouge. The fault's architecture, typical for crystalline environments, poses challenges for fluid flow, necessitating detailed hydraulic and stress characterization before each of the FEAR experiments. This multidisciplinary approach was crucial for managing rock volume heterogeneity and understand implications for the dense monitoring network. Successfully identifying the fault sets the stage for seismic activation experiments commencing in spring 2024.

Authors 16

1. Peter Achtziger-Zupančič Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University · Fraunhofer Research Institution for Energy Infrastructures and Geotechnologies IEG

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Germany

   Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems IEG, Aachen, Germany

2. Alberto Ceccato

   ETH Zurich

   Affiliation as printed

   Department of Earth Sciences, ETH Zurich, Switzerland

3. Alba Zappone

   ETH Zurich

   Affiliation as printed

   Department of Earth Sciences, ETH Zurich, Switzerland

4. Giacomo Pozzi

   Istituto Nazionale di Geofisica e Vulcanologia

   Affiliation as printed

   Istituto Nazionale di Geofisica e Vulcanologia, Italy

5. Alexis Shakas

   ETH Zurich

   Affiliation as printed

   Department of Earth Sciences, ETH Zurich, Switzerland

6. Florian Amann Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University · Fraunhofer Research Institution for Energy Infrastructures and Geotechnologies IEG

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Germany

   Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems IEG, Aachen, Germany

7. Whitney Behr

   ETH Zurich

   Affiliation as printed

   Department of Earth Sciences, ETH Zurich, Switzerland

8. Daniel Escallón Botero

   ETH Zurich

   Affiliation as printed

   Department of Earth Sciences, ETH Zurich, Switzerland

9. Domenico Giardini

   ETH Zurich

   Affiliation as printed

   Department of Earth Sciences, ETH Zurich, Switzerland

10. Marian Hertrich

    ETH Zurich

    Affiliation as printed

    Department of Earth Sciences, ETH Zurich, Switzerland

11. Mohammadreza Jalali corresponding Aachen Department of Engineering Geology and Hydrogeology

    RWTH Aachen University

    Affiliation as printed

    Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Germany

12. Xiaodong Ma

    University of Science and Technology of China

    Affiliation as printed

    School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China

13. Men-Andrin Meier

    ETH Zurich

    Affiliation as printed

    Department of Earth Sciences, ETH Zurich, Switzerland

14. Julian Osten Aachen Department of Engineering Geology and Hydrogeology

    RWTH Aachen University

    Affiliation as printed

    Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Germany

15. Stefan Wiemer

    ETH Zurich

    Affiliation as printed

    Department of Earth Sciences, ETH Zurich, Switzerland

16. Massimo Cocco

    Istituto Nazionale di Geofisica e Vulcanologia

    Affiliation as printed

    Istituto Nazionale di Geofisica e Vulcanologia, Italy