Abstract
Induced seismicity is often associated with fluid injection but only rarely linked to surface deformation. At the Hellisheidi geothermal power plant in south-west Iceland we observe up to 2 cm of surface displacements during 2011–2012, indicating expansion of the crust. The displacements occurred at the same time as a strong increase in seismicity was detected and coincide with the initial phase of geothermal wastewater reinjection at Hellisheidi. Reinjection started on September 1, 2011 with a flow rate of around 500 kg/s. Micro-seismicity increased immediately in the area north of the injection sites, with the largest seismic events in the sequence being two M4 earthquakes on October 15, 2011. Semi-continuous GPS sites installed on October 15 and 17, and on November 2, 2011 reveal a transient signal which indicates that most of the deformation occurred in the first months after the start of the injection. The surface deformation is evident in ascending TerraSAR-X data covering June 2011 to May 2012 as well. We use an inverse modeling approach and simulate both the InSAR and GPS data to find the most plausible cause of the deformation signal, investigating how surface deformation, seismicity and fluid injection may be connected to each other. We argue that fluid injection caused an increase in pore pressure which resulted in increased seismicity and fault slip. Both pore pressure increase and fault slip contribute to the surface deformation.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 106337 |
| Journal | JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH |
| Volume | 391 |
| DOIs | |
| State | Published - Mar 10 2020 |
| Externally published | Yes |
Bibliographical note
KAUST Repository Item: Exported on 2022-06-07Acknowledgements: The authors would like to thank: Einar Gunnlaugsson from Reykjavik Energy (RE) for providing injection data from Hellisheidi; Bjarni Reyr Kristjánsson (RE) for discussions and advice regarding the geothermal power plant operations and tracer tests; Sarah Minson (U.S. Geological Service) for help with CATMIP and letting us use her code; Elías Rafn Heimisson (Stanford University, USA) for advice regarding Coulomb failure stress calculations; David Bekaert (University of Leeds, UK) for helpful advice on the InSAR processing; Sigurjón Jónsson (King Abdullah University of Science and Technology, KSA) for commenting on the manuscript and for providing his Quadtree code; Ólafur Flóvenz (ÍSOR) for comments on the manuscript; the crustal deformation group at IES for help with the GPS measurements in Hengill and discussions on the work in progress. For computing the elastic half-space models we use DMODELS ( Battaglia et al., 2013 ). We would like to thank Philippe Jousset as well as two anonymous reviewers for their thorough review which helped us improve the manuscript. Many of the figures were prepared using the GMT software ( Wessel and Smith, 1991; Wessel et al., 2013 ). The intermediate TanDEM-X digital elevation model used in the InSAR processing was provided by DLR under project IDEM_GEOL0123. COMET is the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics. This work was supported in part by grants from the Iceland Research Fund (grant numbers 130371-051/052/053 and 174377-051 ) and the University of Iceland Research Fund (grant number HI-6489 ). Appendix A
This publication acknowledges KAUST support, but has no KAUST affiliated authors.