Large-N seismic node networks for monitoring seismicity and crustal stress-state at geothermal systems

Geothermal resources are set to play an ever more important role in supplying a sustainable source of energy for the green transition. Here, we present an example of how recent developments in seismic node technology can provide enhanced monitoring of subsurface seismicity and crustal stress-state during geothermal field development. We show results for a network of 450 nodes deployed at a geothermal site in Cornwall, UK, during a well stimulation. A catalogue of 241 earthquakes are detected using a waveform-migration based method. The earthquakes are relocated using double-difference methods and used to map fault structure. Moment magnitudes, stress-drops, fault radii and focal mechanisms are calculated for the catalogue, in order to infer the stress-state of the faults and how fluids interact with the faults. Finally, S-wave velocity anisotropy measurements are used to compare local fault stresses to the orientation of the prevailing, macroscopic crustal stress-state. We find that the significant increase in spatial sampling provided by recent developments in seismic node technology allow us to elucidate fluid-fault interactions in far more detail than would otherwise be possible. These findings show the potential of recent technology advances for monitoring geothermal systems going forward.