Our team published an Open Access paper in Journal of Geophysical Research: Solid Earth entitled “Limited Earthquake Interaction During a Geothermal Hydraulic Stimulation in Helsinki, Finland”. In the manuscript we investigate anthropogenic seismicity associated with fluid injection into the 5.8 km deep geothermal OTN-2 well near Helsinki, Finland, as a part of St1 Deep Heat Project. During injection, a total of 2,875 m3 of fresh water was injected during 16 days at well-head pressures <70 MPa and with flow rates between 400-1000 l/min. Similarly to 2018 stimulation, the seismicity was monitored using a seismic network composed of 20 borehole geophones located in Helsinki area and in the OTN-3 well located close by the injection site. A total of 6,121 earthquakes indicating fractures of 1-30m size were recorded during and after stimulation campaign.
Using a handful of statistical properties derived from earthquake catalog we found no indication for earthquakes being triggered by other earthquakes. Instead, the earthquake activity rates, as well as the maximum earthquake size stayed proportional to the fluid injection rate. The spatio-temporal behavior of seismicity and its properties suggest earthquakes occurred not on a single fault, but in a distributed network of similarly oriented fractures, limiting the possibility for occurrence of violent earthquakes. The performed study provides evidence that the induced seismicity due to injection performed within St1 Deep Heat project is stable and allow to constrain seismic hazard.
Reference:
Kwiatek, G., P. Martínez-Garzón, J. Davidsen, P. Malin, A. Karjalainen, M. Bohnhoff, and G. Dresen (2022). Limited Earthquake Interaction During a Geothermal Hydraulic Stimulation in Helsinki, Finland, Journal of Geophysical Research: Solid Earth 127, no. 9, e2022JB024354, DOI: 10.1029/2022JB024354. [ Article Page ] [ Link to associated data publication ]