D3.3 Guidelines for techniques/methodologies for seismological investigations to be applied in future EGS operations, developed on the basis of successful analyses of past sequences

Our WP3 recommendation, in particular, is based on the analysis of induced seismicity in past sequences from geothermal areas located in different tectonic settings. The geothermal sites investigated include Basel (Switzerland), Berlin (El Salvador), Campi Flegrei (Italy), Krafla, Hengill and Reykjanes peninsula (Iceland), Paralana (Australia), Soultz-sous-Forets (France), and The Geysers, CA (USA). As a general note we strongly recommend to do a quality assessment of the recorded waveforms, and thereafter to apply four different techniques/methodologies for seismological investigations. We recommend to apply (1) a relocation method to reveal small-scale patterns in the induced event location clouds, (2) a spectral ratio technique to improve induced event source parameters, (3) a stress-inversion techniques to relate reservoir hydraulics to the stress field in situ, and (4) a passive continuous ambient seismic noise analysis for imaging changes in mechanical reservoir parameters during and after shut-in. These methods will provide the basis for the secondary well to be drilled. The costs for a thorough analysis of the waveform data practically is negligible when comparing to the costs of a borehole, which should be placed optimally.