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Abstract

Most of the Netherlands is covered with a thick blanket of unconsolidated sediments. In the more consolidated part of the upper crust, different activities are taking place. Oil and gas fields are produced, salt is extracted through solution mining, there is underground storage of liquids and geothermal heat is exploited. All these activities can alter the stress field around existing faults and therewith potentially induce seismicity. Over the years, an extensive seismic network has been built to monitor seismic activity. To find out whether this network suffices to monitor current and future subsurface operations, the network capabilities have been assessed. To that end, new tools have been developed to compute magnitude-of-completeness and location uncertainty maps over the Netherlands. The maps show large spatial variation in network capabilities. The main underlying factor is the large variation of sensor density. Another important factor is sensor placement. On average, noise levels are a factor of 25 lower for 200-deep sensors than for sensors at the Earth's surface, in the frequency band that is used for detection (5 to 40 Hz). Moreover, the local setting is important. A regional network in an urban area performs worse than a similar network in a rural area. The tools also provide a means to study design options for future extensions of the network. A scenario layout can be checked for its capability in terms of the minimum magnitude of locatable earthquakes and their associated uncertainty in location.