Predicting observed induced seismicity due to production in the Hverahlid, SW Iceland, geothermal field

Abstract

The Hverahlíð geothermal field, located in the fissure swarm of Hengill volcano, SW Iceland, has been producing steam and geothermal fluids for the Hellisheiði geothermal power plant (303 MWe, 210 MWth), since late 2016.  A total of 7 geothermal wells in the field (HE-21, -26, -53, -54, -60, -61 and -66) have been producing up to 150 kg/s of steam and 60-70 kg/s of separated liquid.  The combined extraction from the wells is limited by the size of the steam pipeline connecting the field to the power plant.   Within months of the initiation of production an increase in seismicity was noted within the field.  This is in contrast to the nearby Hellisheiði geothermal field, ~2 km away, which has experienced very little induced seismicity since commission in 2006, despite more than twice as high mass extraction rates and higher deformation rates.  Since early 2018 a total of 8 events with M> 2.5 have occurred in the field.  The latest of these events occurred in November 2022 with M 3.2. The seismicity largely does not line up on faults and is relatively evenly distributed throughout what is considered the top of the geothermal reservoir (Kristjánsdóttir et al 2019). Currently a second pipeline connecting the geothermal field with the power plant is in construction and with the commission, planned for fall 2024, an increase in mass extraction rates from the Hverahlíð geothermal field  of ~30% is expected. In this presentation we compare the observed location, seismicity rates and Mmax values to those expected from different models of earthquake triggering.  We furthermore predict the expected increase in seismicity rates due to the increase in production rates and the increase in seismicity that will be felt by the neighboring community of Hveragerði.