Plate Divergence at the Krafla Volcanic System, Iceland: Insight From GNSS Geodesy and Sentinel‐1 Satellite Radar Interferometry in 2002–2024

Abstract

The Krafla volcanic system in Iceland, a subaerial segment of the divergent boundary between the North American and Eurasian plates, offers a unique opportunity to investigate volcano‐tectonic processes. We present a six‐segment kinematic back slip plate boundary model constrained jointly by long‐term deformation velocity fields from Global Navigation Satellite System (2002–2024) and Sentinel‐1 SAR interferograms (2015–2023). The inferred plate boundary axis passes through the middle of the Krafla caldera and follows recent eruptive fissures. Its orientation varies between N1.2°–N10.8°E within and south of the central volcano but rotates to NNW‐SSE north of it. For this preferred axis geometry, the inferred spreading rate is mm/yr in an azimuth of ° (formal uncertainties corresponding to 95% confidence interval of the Bayesian inversion results). Locking depth varies significantly along the plate boundary axis: it is shallowest within and just north of the Krafla caldera ( km) and deepens to and km to the north and south, respectively. This variation is consistent with the depth distribution of seismicity and reflects an up‐doming brittle‐ductile transition along the fissure swarm. These first‐order features remain robust, although uncertainties increase when the axis location is allowed to vary. After correcting vertical velocities for glacial isostatic adjustment and regional subsidence caused by extensional rheological anomalies, residual velocities reveal three areas of local deflation: two related to the Krafla and Bjarnarflag geothermal fields and one at the northernmost part of the 1975–1984 Krafla lava field. Therefore, detailed plate boundary models can provide insights into crustal rheology, volcano‐tectonic interactions and local processes.