Seismic network design to detect felt ground motions from induced seismicity

Human activities, such as fluid injection as part of the stimulation of an enhanced geothermal system (EGS) for heat and power production, can cause damaging earthquake ground motions. A difficulty in quickly settling or rejecting insurance claims to the policy of the EGS operator is the lack of ground truth on the observed shaking at sites of reported damage. To overcome this problem a local seismic network could be installed prior to injection to constrain the ground-motion field at points of potential damage. Since the installation and maintenance of seismometers are costly there is an incentive to keep the number of instruments to a minimum. In this short communication, ground-motion fields are simulated and receiver operating characteristic analysis is conducted to guide decisions on the number of sensors required to obtain a certain confidence in the rate of false alarms and missed detections. For densities of 10-20 instruments per km² the ability to estimate potentially damaging ground motions is reasonable but associated with a significant chance of missed detections and false alarms. If an EGS operator or regulatory authority does not want to accept such chances then network densities of 50-100 instruments per km² are required and even in this case the exceedance/non-exceedance of a certain ground-motion threshold cannot be completely constrained.