The role of Coulomb stress changes for injection‐induced seismicity: The Basel enhanced geothermal system

[1] We estimate Coulomb stress variations (ΔCFS) by considering interactions among 163 earthquakes (ML ≤ 3.4) that occurred during the hydraulic stimulation of the enhanced geothermal system in Basel, Switzerland, in 2006. We observe that overall 75% of event locations are consistent with positive ΔCFS. The performance of the model increases with time and distance from injection, accordingly with the presumed less dominant role of the pore pressure further from the injection well and after shut-in. We analyze the sensitivity of results to location and focal mechanism uncertainties, the fault-plane ambiguity, and the friction coefficient. We find that ΔCFS are highly sensitive to location accuracy but robust with regard to uncertainties of the other parameters. Our results suggest that (i) the Coulomb model may complement conventional pore-pressure triggering models and (ii) implementing it for time-dependent seismic hazard assessment during fluid injection may improve the forecasting ability but will require highly accurate hypocenter estimates.

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