Evidence for Tensile Faulting from Full Waveform Moment Tensor Inversion of Induced Seismicity in Basel Geothermal Site

In summary, we have performed a full waveform inversion to retrieve both double couple (DC) and moment tensor (MT) source parameters for the 19 strongest induced microseismic events at the Basel geothermal site. The DC solutions agree well with the result from a previous study based on the fitting of projected P wave first-motion polarities at ~40 stations. In comparison, data from less than ten (mostly six) stations has been used in our study. The analysis of MT solutions indicates the presence of significant ISO components, including both fracture opening and closing, for events occurring during and immediately after the injection and pure DC solutions for later events. The spatio-temporal pattern of isotropic components of the moment tensor can be explained by the pore pressure perturbation.