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Abstract:
We have recently developed a new physics-based seismicity model assuming pre-existing populations of faults that respond to changes in Coulomb stress. In contrast to the traditional Coulomb Failure (CF) model, which assumes instantaneous triggering when stress exceeds a threshold value, the new model replaces instantaneous triggering with an average time to failure that depends exponentially on the absolute stress value. The prediction for critical pre-stress conditions is identical to the widely used rate-state (RS) friction model. Thus, CF and RS predictions are both special cases of the new model. However, the new stress response model can also account for subcritical initial stress conditions, which are particularly relevant for induced seismicity in intraplate regions.
Here we show the application of the new model to the Groningen gas field, which is one of the largest onshore gas fields in production in Europe and a frequently considered site for the study of induced seismicity. The long delay between the start of production and the onset of seismicity indicates subcritical pre-stresses. We estimate the pre-stress distribution based on the background stress field and the existing fault structure. Using this pre-stress distribution and the estimated temporal evolution of the 2D stress field in the reservoir, we show that the delayed onset, the peak in 2013-2015 and the recent decline in observed seismicity are well explained by the model.
