We further develop the Back Projection technique for tracing the rupture propagation of microseismic events. We lay out the basic idea of Back Projection imaging and show the results for three synthetic datasets obtained using finite-difference modeling. The synthetic rupture models in use where generated according to microseismic events that occurred at the Basel EGS. They help us to understand the influences of the station geometry and the station weighting process which need to be applied in Back Projection imaging. The focus of the work lies in the analysis of real events and the extraction of their respective properties. We show the corresponding results for the four largest real events of local magnitudes M=3.1–3.4 from the Basel EGS site and discuss the validity and interpretation of the outcome. We find that the obtained rupture dimensions are consistent with the independent magnitude derived estimates. The rupture directions which are obtained fit reasonably well to the shape of the microseismic cloud and to one of the respective fault planes obtained from source mechanism analysis. This supports the validity of our approach. In addition we are hereby capable of solving the fault plane ambiguity.


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