Kinematic and Dynamic Source Parameters of Induced Earthquakes at St. Gallen Geothermal Field, Switzerland

Abstract The exploitation of the St. Gallen geothermal reservoir in Switzerland induced a seismic sequence lasting from July 2013 to October 2013. The sequence was characterized by 346 earthquakes located at a depth ranging between 4.4 and 4.7 km, having magnitude ranging between (−1.2, 3.5). We study the seismic source properties of the induced earthquakes by implementing both the individual earthquake displacement spectral inversion and an empirical Green's function‐based method that allows to reduce the trade‐off between source parameters and anelastic attenuation. We find a scaling between corner frequency and seismic moment down to 5 × 10 10 Nm that differs from the generally assumed M 0 ∝ f c −3 . The retrieved average value of the static stress drop (3.8 MPa) is close to the median global value (4 MPa) observed for tectonic earthquakes and it is a small fraction (0.1%–20%) of the shear stress resolved on the fault planes. Moreover, we find that the analyzed events are characterized by low Savage‐Wood efficiency indicating a positive dynamic overshoot suggesting that only a small fraction of the available strain energy is radiated seismically.