loading page

Limited earthquake interaction during a geothermal hydraulic stimulation in Helsinki, Finland
  • +4
  • Grzegorz Kwiatek,
  • Patricia Martínez-Garzón,
  • Jörn Davidsen,
  • Peter Eric Malin,
  • Aino Karjalainen,
  • Marco Bohnhoff,
  • Georg Dresen
Grzegorz Kwiatek
Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences

Corresponding Author:[email protected]

Author Profile
Patricia Martínez-Garzón
Helmholtz Centre Potsdam GFZ German Research for Geosciences
Author Profile
Jörn Davidsen
University of Calgary
Author Profile
Peter Eric Malin
Advanced Seismic Instrumentation & Research
Author Profile
Aino Karjalainen
St1 Oy
Author Profile
Marco Bohnhoff
Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences
Author Profile
Georg Dresen
GFZ Potsdam
Author Profile


We investigate induced seismicity associated with a hydraulic stimulation campaign performed in 2020 in the 5.8 km deep geothermal OTN-2 well near Helsinki, Finland as part of the St1 Deep Heat project. 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. The seismicity was monitored using a high-resolution seismic network composed of 10 borehole geophones surrounding the project site and a borehole array of 10 geophones located in adjacent OTN-3 well. A total of 6,121 induced earthquakes with local magnitudes were recorded during and after the stimulation campaign. The analyzed statistical parameters include magnitude-frequency b-value, interevent time and interevent time ratio, as well as magnitude correlations. We find that the b-value remained stationary for the entire injection period suggesting limited stress build-up or limited fracture network coalescence in the reservoir. The seismicity during the stimulation neither shows signatures of magnitude correlations, nor temporal clustering or anticlustering beyond those arising from varying injection rates. The interevent time statistics are characterized by a Poissonian time-varying distribution. The calculated parameters indicate no earthquake interaction. Focal mechanisms suggest that the injection activated a spatially distributed network of similarly oriented fractures. The seismicity passively responded to the hydraulic energy input rate, with the cumulative seismic moment proportional to the cumulative hydraulic energy and maximum magnitude controlled by injection rate. The performed study provides a base for implementation of time-dependent probabilistic seismic hazard assessment for the project site.
Sep 2022Published in Journal of Geophysical Research: Solid Earth volume 127 issue 9. 10.1029/2022JB024354