Effective Detection Capability of a Local Seismic Network

In applications such as geothermal energy, underground storage, mining, hydraulic fracturing, it becomes current practice to implement local seismic networks to monitor induced seismicity and to help mitigating the associated risks. In such contexts, it is crucial to guarantee that the network is able to detect a seismic event of predefined magnitude in a specific area. We propose a method to estimate this detection capability for existing kilometric-scale seismic networks which did not record any seismicity in the target zone yet. However, the network should be running for a time period long enough to record several local events listed in a reference catalogue. These earthquakes are used to calibrate an amplitude-magnitude relationship, knowing that the amplitudes are at the basis of the detection of seismic event candidates. This observation-based approach can take into account uncertainties in the magnitude estimate. The procedure was applied on the seismic network deployed over Bruchsal (Germany) geothermal field. Since mid-2010, no seismicity in the reservoir has been recorded by the network despite its good working order. The proposed technique suggests that there is 95% probability that no seismic event with ML ≥ 0.7 occurred below the network down to the reservoir depth at 2400 m.