It is known for more than 30 years that seismic events can be induced during the development or the exploitation of geothermal reservoirs, and especially Enhanced Geothermal Systems (EGS). This offers a unique opportunity to characterize several properties of the geothermal reservoir, starting with its geometry. However, if too strong, induced seismicity can also become a serious concern and prevent from further development of a geothermal project. Hence, better understanding of the relationships between the in situ stress field, the geomechanical properties of the faults, and the induced seismicity is key for sustainable use of this renewable energy. This constitutes one of the main research interests of our team.

Induced seismicity and geothermal well logs are preferential observations used to investigate the problematics. Several past and current analyses, which were performed in our team, focus on:

• Static stress transfer due to seismic events,

• Variation of the in situ stress, in depth and time, derived from the seismicity induced during an EGS stimulation,

• Sensitivity analysis of seismic monitoring network to variation of P- and S-wave velocities,

• Slip tendency analysis and dilation tendency analyses of geothermal fields in the Upper Rhine Graben, and in the Molasse basin

• Local stress heterogeneity and borehole breakout variations due to active fractures,

• Clay zone identification in crystalline well logs,

• Correlation between seismic / aseismic behaviour of faults and clay content

The Soultz-sous-Forêts (France, Alsace) EGS is one of our main field of application. Besides, our team is involved in the seismic monitoring of the Rittershoffen (France, Alsace) EGS under development and the Bruchsal (Germany, Baden-Württemberg) hydrothermal field. Waveform-based techniques (e.g. time reverse imaging, migration) to process induced seismicity and to estimate the seismic source characteristics are development axes.