A Monte Carlo Method for Probabilistic Hazard Assessment of Induced Seismicity due to Conventional Natural Gas Production by S. J. Bourne, S. J. Oates, J. J. Bommer, B. Dost, J. van Elk, and D. Doornhof Abstract A Monte Carlo approach to probabilistic seismic-hazard analysis is de- veloped for a case of induced seismicity associated with a compacting gas reservoir. The geomechanical foundation for the method is the work of Kostrov (1974) and McGarr (1976) linking total strain to summed seismic moment in an earthquake cata- log. Our Monte Carlo method simulates future seismic hazard consistent with histori- cal seismic and compaction datasets by sampling probability distributions for total seismic moment, event locations and magnitudes, and resulting ground motions. Ground motions are aggregated over an ensemble of simulated catalogs to give a prob- abilistic representation of the ground-motion hazard. This approach is particularly well suited to the specific nature of the time-dependent induced seismicity considered. We demonstrate the method by applying it to seismicity induced by reservoir com- paction following gas production from the Groningen gas field. A new ground-motion prediction equation (GMPE) tailored to the Groningen field, has been derived by cal- ibrating an existing GMPE with local strong-motion data. For 2013–2023, we find a 2% chance of exceeding a peak ground acceleration of 0:57g and a 2% chance of exceeding a peak ground velocity of 22 cm= s above the area of maximum compaction. Disaggregation shows that earthquakes of M w 4–5, at the shortest hypocentral dis- tances of 3 km, and ground motions two standard deviations above the median make the largest contributions to this hazard. Uncertainty in the hazard is primarily due to uncertainty about the future fraction of induced strains that will be seismogenic and how ground motion and its variability will scale to larger magnitudes. Introduction Several energy technologies have been observed to have the potential for causing induced earthquakes (e.g., Majer et al., 2007; Suckale, 2009; Evans et al., 2012; Davies et al., 2013; Ellsworth, 2013; Klose, 2013; National Academy of Sciences [NAS], 2013; International Energy Agency Envi- ronmental Projects Ltd. [IEAGHG], 2013), and in recent years public awareness and concern regarding the possible impacts of such events has grown. Operators and regulators alike need to make risk-informed decisions for the manage- ment of the threat that may be posed by such projects, in which risk may be thought of as the product of hazard, ex- posure, and vulnerability. Seismic-hazard assessments are essential to inform the choice of any risk mitigation options. The design and implementation of any risk mitigation measures necessarily must begin with a quantification of the ground-shaking hazard due to induced seismicity. The well-established approaches used to analyze ground-shaking hazard due to natural seismicity cannot be directly applied to induced earthquakes. The main challenge lies in the fact that induced seismicity, unlike natural tectonic earthquake activ- ity, cannot be treated as stationary in time, which is a stan- dard assumption in probabilistic seismic-hazard analysis (PSHA). Time-dependent PSHA models have been developed but these are usually based on short-term probabilities of events considering the current position in the seismic cycle (e.g., Petersen et al., 2007; Akinci et al., 2009) or the effects of Coulomb stress transfer following large earthquakes (e.g., Parsons et al., 2000). The problem of induced seismicity, in which the recurrence characteristics may increase signifi- cantly over a short period of time (and then possibly recede to background levels in the longer term), requires the devel- opment of different approaches. Additionally, the models de- veloped need to accommodate earthquakes over magnitude ranges that are quite different (i.e., much smaller values) than those considered in PSHA for natural seismicity, and the fact that these will generally occur at very shallow depths. Responding to the growing public and regulatory con- cerns about induced seismicity, hazard assessment ap- proaches have been developed in recent years, particularly for enhanced geothermal systems (Convertito et al., 2012; Mena et al., 2013). Because the mechanism by which in- duced earthquakes are caused by energy production or waste 1 Bulletin of the Seismological Society of America, Vol. 105, No. 3, pp. –, June 2015, doi: 10.1785/0120140302