Abstract

Understanding seismicity and hydro-mechanical processes during hydraulic stimulation in hectometer-scale in-situ experiments is an important step for bridging the gap between laboratory studies and deca-meter scale in-situ experiments on the one hand and large-scale geothermal projects on the other hand. These insights can help to optimize the use of geothermal energy. A key example of such a project on the hectometer scale is the Bedretto Underground Laboratory in Switzerland, where multiple hydraulic stimulation experiments were conducted between 2021 and 2023. In this study, we present the seismic event processing steps adapted to mesoscale experiments, providing a framework for future mesoscale projects. We outline two main goals for seismic catalog creation of hydraulic stimulations: First, the development of real-time catalogs aimed at hazard assessment, which prioritize the detection of large-magnitude events. These catalogs are optimized for rapid decision-making but may overlook smaller events. Second, we focus on post-processed catalogs designed for detailed analysis of activated fracture networks, where a complete seismic catalog is essential. Additionally, we evaluate the influence of picking accuracy, homogeneous 1D velocity model, and the network coverage on the final event locations in the context of a mesoscale underground 3D seismic network, a novelty in experimental seismology. This analysis highlights the sensitivity of picoseismic event locations to these factors, providing critical insights for accurate seismic monitoring in complex geological settings.