| Title | Induced Seismicity During Reinjection of Wastewater in Hellisheidi Geothermal Field, SW Iceland |
|---|---|
| Authors | Sigridur KRISTJANSDOTTIR, Olafur GUDMUNDSSON, Kristjan AGUSTSSON, Thorbjorg AGUSTSDOTTIR, Ari TRYGGVASON, Michael FEHLER |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Induced seismicity, wastewater injection, Hellisheidi geothermal field |
| Abstract | In 2011 and 2012, a large number of earthquakes were induced during the reinjection of wastewater at the Hellisheidi geothermal power plant near the Hengill volcano in SW Iceland. The area is tectonically active, located close to the triple junction of an oblique spreading zone (Reykjanes Peninsula), a rift zone (the Western Volcanic Zone) and a transform zone (the South Iceland Seismic Zone). The injection started in September 2011 and the seismici-ty increased shortly after, with thousands of events recorded in the following months by the local network of the Icelandic Meteorological Office (IMO). The majority of events were small (Ml less than 3.0), but the two largest events reached Ml 3.8 and were widely felt in the area. An increase in seismicity was also observed during the drilling of the injection wells, associ-ated with the loss of drilling fluid. From 2009 until 2013, Uppsala University, Massachusetts Institute of Technology, Reykjavik University, and Iceland GeoSurvey operated a dense temporary network of seismographs in the area. Data from this temporary network and the permanent IMO network was used to make a detailed analysis of the induced seismicity. The events that had been located by the IMO network were grouped into families based on waveform similarity. By using a typical event from each family as a template for cross correlation of the continuous dataset, we were able to quadruple the number of previously located events. Cross correlation differen-tial travel time measurements were then used to relocate the expanded dataset of events with high accuracy. The time delay measurements were performed in the frequency domain ensuring subsample precision. We analyzed the spatial and temporal relationship between earthquakes and injection processes, and calculated focal mechanisms for the master events, giving an insight into the local stress field. The authors would like to acknowledge the IMO for access to waveform data. |