Seismic Network (data acquisition system, seismometers, accelerometers, DAS interrogator unit)

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Cologne is the only German city with more than one million inhabitants exposed to a significant seismic hazard. The surrounding Lower Rhine Embayment also includes several large-scale open-pit lignite mines. This proposal aims to refurbish the strong motion network ot the Bensberg seismic observatory, consisting of 23 stations within 60 km of Cologne, and enhance the performance of the existing seismic networks by adding five new strong motion and five new microseismic stations as well as an innovative laser-based DAS (Distributed Acoustic Sensing) interrogator unit that can measure ground motion with unprecedented spatial resolution by using light scattering in optical fibres. The data acquisition of the strong motion network has been in continuous 24/7 operations for the past 15 years and is increasingly prone to failures. Besides, it is outdated and no longer compatible with current (64-bit) computers, so it needs to be replaced completely. The new data acquisition will provide continuous real-time data access and produce data in a standard format, for easy exchange and sharing via European Open Data initiatives and closer collaboration with neighbouring seismological surveys. The main aim of the strong motion network, besides aiding in locating microseismic events in the vicinity of each individual station, is the unclipped recording of ground motion in case of strong earthquakes. These recordings, also at locations close to the source, are instrumental for deriving parameters of relevance to earthquake engineering, and accordingly in developing ground motion prediction equations for the region and estimating seismic hazard. Since large earthquakes are rare in the Lower Rhine Embayment (i.e. have an estimated recurrence interval of 15 to 20 years for magnitude 5.0), continuous long-term monitoring is mandatory. The additional strong motion stations will help to address the question of the influence of recultivated areas vs. naturally deposited sediments on the amplitudes of ground motion, which is of high relevance for estimates of seismic ground motion in the areas affected by open-pit lignite mines. Additional microseismic stations will increase the detection efficiency and performance of the network in microseismic monitoring. The DAS interrogator unit provides new observables with multiple benefits, e.g. to earthquake location, mapping of faults, studying the sub-surface structure and its small-scale variations, which have important implications for amplification of ground motion during earthquakes. We aim to use the DAS interrogator unit in dedicated measurement campaigns, e.g. across known or suspected faults, in areas with sedimentary cover where a better knowledge of the elastic parameters of the subsurface would be beneficial for both hazard assessment and microseismic event location, or in aftershock monitoring, to make the best use of this innovative technology.