Seismic monitoring is essential for understanding subsurface processes, particularly in geothermal operations where low-magnitude events can provide valuable insights into reservoir behaviour. There are two significant challenges when monitoring the seismicity in Dutch geothermal operations: (1) detecting signals from seismic events as noise levels are typically high in regions hosting geothermal operations, and (2) accurately estimating their corresponding hypocentre and uncertainty. In this study, we present a comprehensive workflow for detecting and characterising low-magnitude seismic events. Specifically, we integrated data preparation, template-matching and machine-learning-based event detection, and probabilistic hypocentre estimation. Applying this workflow to 4 months of recordings in Kwintsheul, Netherlands, we detected 65 events with coherent signals, including six weak seismic events (ML < 0.0) near a local fault and a geothermal injection well. These events suggest the presence of a recurring microseismic sequence previously unreported in the area. However, spatial uncertainties, the short monitoring period, and the limited azimuthal coverage make the nature of these events unclear. Our findings highlight the importance of improving network design and refining velocity models to reduce uncertainties in event locations and magnitudes. The proposed workflow offers a scalable solution for enhancing seismic monitoring, particularly in urban and geothermal settings.

This presentation gives an overview of the ACT3 SHARP Storage project (Stress history and reservoir pressure for improved quantification of CO2 storage containment risks), introducing its ongoing seismological activities. This includes building a new earthquake catalogue for the North Sea area and designing improved seismic monitoring schemes for CO2 storage sites using seismic networks, seismic arrays, and distributed acoustic sensing on fibre-optic cables. The SHARP Storage project was launched in late 2021 with the overall aim to increase accuracy of subsurface CO2 storage containment risk management through the improvement and integration of subsurface stress models, rock mechanical failure and seismicity observations. SHARP is collaboration between 16 research institutions and companies and is supported under the ACT3 call. ACT is an ERA NET Cofund, which is a tool established by the European Commission under the Horizon 2020 programme for research and innovation. More information on the SHARP Storage project is found at https://sharp-storage-act.eu/.