Geothermal energy is a viable alternative to gas for the heating of buildings, industrial areas and greenhouses, and can thus play an important role in making the transition to sustainable energy in the Netherlands. Heat is currently produced from the Dutch subsurface through circulation of water between two wells in deep (1.5–3 km) geothermal formations with temperature of up to ∼100 °C. As the number of these so-called doublets is expected to increase significantly over the next decades, and targeted depths and temperatures increase, it is important to assess potential show-stoppers related to geothermal operations. One of these potential hazards is the possibility of the occurrence of felt seismic events, which could potentially damage infrastructure and housing, and affect public support. Such events have been observed in several geothermal systems in other countries. Here we review the occurrence (or the lack) of felt seismic events in geothermal systems worldwide and identify key factors influencing the occurrence and magnitude of these events. Based on this review, we project the findings for seismicity in geothermal systems to typical geothermal formations and future geothermal developments in the Netherlands. The case study review shows that doublets that circulate fluids through relatively shallow, porous, sedimentary aquifers far from the crystalline basement are unlikely to generate felt seismic events. On the other hand, stimulations or circulations in or near competent, fractured, basement rocks and production and reinjection operations in high-temperature geothermal fields are more prone to induce felt events, occasionally with magnitudes of M > 5.0. Many of these operations are situated in tectonically active areas, and stress and temperature changes may be large. The presence of large, optimally oriented and critically stressed faults increases the potential for induced seismicity. The insights from the case study review suggest that the potential for the occurrence of M > 2.0 seismicity for geothermal operations in several of the sandstone target formations in the Netherlands is low, especially if faults can be avoided. The potential for induced seismicity may be moderate for operations in faulted carbonate rocks. Induced seismicity always remains a complex and site-specific process with large unknowns, and can never be excluded entirely. However, assessing the potential for inducing felt seismic events can be improved by considering the relevant (site-specific) geological and operational key factors discussed in this article.

Seismic interferometry applied to ambient-noise measurements allows the retrieval of the seismic response between pairs of receivers. We studied ambient-noise seismic interferometry (ANSI) to retrieve time-lapse reflection responses from a reservoir during CO 2 geologic sequestration, using the case of the experimental site of Ketzin, Germany. We applied ANSI to numerically modeled data to retrieve base and repeat reflection responses characterizing the impedances occurring at the reservoir both with and without the injection of CO 2 . The modeled data represented global transmission responses from band-limited noise sources randomly triggered in space and time. We found that strong constraints on the spatial distribution of the passive sources were not required to retrieve the time-lapse signal as long as sufficient source-location repeatability was observed between the base and the repeat passive survey. To illustrate the potential of the technique, ANSI was applied to three days of passive field data recorded in 2012 at Ketzin. Comparison with the modeled results illustrated the potential to retrieve key reflection events using ANSI on field data from Ketzin. This study supports the idea that the geologic setting and characteristics of ambient noise at Ketzin may be opportune to monitor CO 2 sequestration.

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