Tectonic Stress as the Driving Mechanism for Dike Opening in an Oblique Rift Setting: A Deformation Model of the 2021 Fagradalsfjall Dike, Iceland

Abstract

Repeated dike-intrusions often occur in zones where extensional stress has accumulated. Still, geodetic modeling of observed dike-induced ground deformation often ignores the contribution of tectonic stress. On the obliquely spreading Reykjanes Peninsula, Iceland, tectonic strain build-up had been geodetically documented for three decades when a magmatic dike formed at Fagradalsfjall in 2021. We explore the contribution of tectonic stress on dike emplacement in a viscoelastic three-dimensional Finite-Element deformation model. Tectonic stress accumulation is initially simulated through plate motion, and later partially released by opening of a segmented rectangular dike. We find that surface deformation can be largely reproduced by releasing $\sim$60% of the accumulated tectonic stress. Partial stress release and low magma overpressure are consistent with successive dike intrusions and low-intensity eruptions in the area. Our model provides an approach to consistently model stress-release constrained by surface deformation.