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Numerical models reproducing the seismic evolution in gas fields can be utilized to study the characteristics of compaction‐induced seismicity during production and thus derive valuable information for the assessment of the seismic hazard. Here, we present a numerical approach for a Rotliegend gas field in Northern Germany ("reference field"), consisting of the simulation of poro‐elastic stresses within a 3D finite element model. Fault stability is controlled by Coulomb friction, whereas the post‐failure process is implemented using a slider‐block model. The model successfully computes seismic sequences, which reproduce the main characteristics of the observed seismicity in the reference field: the location, the temporal seismic evolution, including the retarded onset several years after the beginning of production, the high prevalence of moderate magnitudes, the observed maximum magnitude and cumulative seismic moment release. The numerical simulations reveal that seismicity‐driving stresses are restricted to the vicinity of fault intersections with the top and bottom of the reservoir, respectively. Slip frequently extends beyond the vertical boundaries of the reservoir, although the failure process is generally self‐arrested outside the reservoir boundaries. The magnitude frequency distribution of observed and simulated earthquakes deviates from the log‐linear behavior frequently assumed in seismic hazard assessments. Instead, the earthquake activity is consistent with a "characteristic earthquake" model, where a fault repeatedly hosts earthquakes with a specific maximum magnitude. Our analysis indicates that production‐induced seismicity is primarily controlled by poro‐elastic stress changes rather than by unknown details of subsurface conditions. This allows for a prognosis of future seismicity and associated hazard. Plain Language Summary: Seismicity induced by gas production in Northern Europe exhibits an unusual signature compared to seismicity associated with other subsurface technologies. Moderately strong earthquakes appear after several years of production, frequently without any smaller‐sized precursors. A so far unanswered question is whether the magnitude of the strongest earthquakes continues to increase during ongoing gas production or stays at a moderate magnitude level. We have developed a numerical model to simulate induced seismicity caused by gas production at a field in Northern Germany. Initially, we model the gas depletion and the associated changes in the stress conditions in the subsurface. Subsequently, we simulate earthquakes triggered by these stress changes with a block‐spring approach, where subsurface faults consist of a large number of undeformable but interconnected blocks. The strength of each earthquake at a certain time is mainly determined by the area of simultaneously activated blocks. The results of these simulations indicate that the maximum earthquake strength remains constant with ongoing gas production. The earthquake of maximum strength is subjective to each fault and may occur several times. This finding is crucial regarding the assessment of the seismic hazard for producing gas fields in Northern Europe. Key Points: A physics‐based model reproduces the most important characteristics of gas production‐induced seismicity in a field in Northern GermanyEarthquakes originate at the reservoir boundaries and may propagate into the surrounding rock, where the failure process is self‐arrestedSeismicity on each fault is characterized by a recurring maximum magnitude [ABSTRACT FROM AUTHOR]

The 9.1 km deep KTB (Kontinentale Tiefbohrung, Germany) drilling hole is one of the best investigated deep-drilling sites in the world. Among other parameters, in situ measurements revealed continuous profiles of principal stresses, pore fluid pressure and fracture geometry in the vicinity of the borehole. The present study combines these parameters with hydraulic and seismicity data obtained during fluid-injection experiments conducted at the KTB to derive a conceptual model for fluid-injection-induced seismicity at the KTB. This model rests on the well constrained assumptions that (1) the crust is highly fractured with a permeable fracture network between 9 km depth and the Earth's surface and (2) the crust is in near-failure equilibrium, whereby a large number of fracture planes are under near-critical condition. During the injection experiment, the elevated pore fluid pressure remained well below the least principal stress and thus was too small to cause hydraulic opening of existing fractures. Consequently, the geometry of the fracture network was assumed to have not changed during fluid injection with induced seismicity occurring solely as a result of lowering of the effective normal stress, consistent with observed source mechanisms. The key parameter in the present model is the fracture permeability, which exhibits large spatial and directional variations. These variations are proposed to primarily control fluid migration paths and associated propagation of elevated fluid pressure during fluid injection. In contrast with common models based on isotropic fluid diffusion or spatially averaged permeability, highly permeable branches of the fracture network strongly affect the propagation of fluid pressure and prohibit the concept of a smooth 'pressure front'. We find evidence that major fluid flow exists at comparatively low fluid pressure (below the critical pressure required to cause seismic failure) without being detected seismically. This might also... [ABSTRACT FROM AUTHOR]