[SSS04-P01] Constraint of focal mechanisms of induced seismicity by using misfit angles based on known in-situ stress
Keywords:Induced seismicity, Focal mechanism, In-situ stress
We proposed a method to improve the estimates of focal mechanisms by introducing in-situ stress information from borehole logging information. We eliminate candidate focal mechanisms that are consistent with first motion data but cannot have shear slip under a given stress state and pore pressure increase. In this study, we also check the consistency between the shear slip vector estimated from the stress state and the rakes. We compare the shear slip vector and the slip vector from the rake. Then we reject the fault if the difference in the two vectors is significantly large. With this process, we reject the fault planes and auxiliary planes which are not consistent with stress state. We apply this method to induced seismicity dataset from Basel, Switzerland, where we already have well-constrained focal mechanisms estimated by many surface stations over a large region. We use these focal mechanisms as references to check whether our method can constrain the range of focal mechanisms using a small number of nearby stations. We find that the consistency check between two vectors significantly and reliably limits the range of focal mechanisms. Furthermore, we combine the constrained range of focal mechanism by this method and that by stability analysis to have more constraint of focal mechanisms satisfying the conditions of the geomechanical problem.