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Tectonic stress release through dike emplacement constrained by surface deformation: Finite Element modeling of the 2021 Fagradalsfjall dike, Iceland

Sonja H. M. Greiner1,2,3 , Freysteinn Sigmundsson1, Halldór Geirsson1, Steffi Burchardt2,3, Olivier Galland4

  • Affiliations: 1 Nordvulk, Institute of Earth Sciences, University of Iceland, Iceland 2 Department of Earth Sciences, Uppsala University, Sweden 3 Center for Natural Hazard and Disaster Science (CNDS), Sweden 4 NJORD Center, Department of Geosciences, University of Oslo, Oslo, Norway 

  • Presentation type: Talk

  • Presentation time: Friday 10:45 - 11:00, Room R380

  • Programme No: 2.3.8

  • Theme 2 > Session 3

Abstract

At divergent plate boundaries, tectonic stress accumulates due to plate motion over time and may be released through rifting episodes and dike emplacement. Although the importance of tectonic stress for magmatic intrusions in this context is well known, it is rarely directly considered in surface deformation models. In 2021, a magmatic dike formed in the Fagradalsfjall volcanic system, SW-Iceland, ending almost 800 years of volcanic quiescence on the obliquely spreading Reykjanes Peninsula. Dike emplacement was accompanied by intense seismicity and ground deformation, which was geodetically well documented. We implement a Finite Element deformation model to explore and quantify the contribution of tectonic stress as a driving mechanism for dike emplacement, using the 2021 Fagradalsfjall dike as a case study. First, tectonic stress accumulates due to oblique plate motion in a viscoelastic model. Secondly, dike opening locally releases a part of the accumulated tectonic stress. We found that geodetic observations can be reproduced reasonably well when ca. 60% of the accumulated tectonic stress is released. In oblique tectonic settings, shearing above the dike may help to distinguish between dikes driven largely by tectonic stress or by magmatic overpressure. Tectonic stress as the dominant driving mechanism for dike emplacement at Fagradalsfjall in 2021 is consistent with low magma flow rates at the onset of the eruption and partial stress release is consistent with subsequent dike intrusions between 2021-2023. Our model helps to better understand volcano-tectonic interaction on the Reykjanes Peninsula and to consistently model stress release constrained by surface deformation.