Seismological study of the geothermal field laboratory in the Lower Rhine Embayment, Germany

The Lower Rhine Embayment in Germany may contain part of the largest hydrothermal reservoir in Europe. In Belgium and the Netherlands, related stratigraphical units have already been developed for geothermal energy provision. At the site of RWE's lignite-fired power plant in Weisweiler, about 15 km east of Aachen, a Fraunhofer research power plant is therefore envisioned and will be explored for the use of deep geothermal energy. Weisweiler is located in seismic zone 3 according to DIN 4149 (2005), due to past activity along several NW-SE trending normal faults in the Lower Rhine Graben system. Extensive exploration work is planned to estimate the risk of induced or triggered seismicity and to better understand the geological and geomechanical setting. Complementary to other geophysical and geomechanical studies, a temporary seismic network with more than 40 seismic surface stations was installed in summer 2021 for a period of approximately 10 months to evaluate the natural seismicity in the region. The temporary seismic network consists of 27 broadband stations and 20 short period geophones from the Ruhr-University Bochum and the Geophysical Instrument Pool Potsdam (GIPP). The inter-station spacing of the network is about 2 km and the total extent of the network is about 20 km. Since the study area is a densely populated area, site selection must be considered carefully to ensure data quality. Here we report on the seismic network design and performance and show preliminary results, including detection and location of natural seismicity. Specifically, we compare the differences between waveform-based and standard phase-picking based methods for locating events and obtaining focal mechanisms. We will also investigate the propensity for remote dynamic triggering in the region and report on the current status of subsurface seismic velocity information obtained using ambient seismic noise.