Fault Systems and Dyke-Induced Deformations: Insights from Drone Surveys and Numerical Modelling in the Fremri-Námur Area, Northern Iceland

The Fremri-Námur Fissure Swarm (FFS), located in the northern sector of the Icelandic rift, represents an ideal natural laboratory for investigating the interactions between magmatic intrusions and surface deformation. This region features a complex system of volcanic edifices, eruptive fissures, extensional fractures, and primarily normal faults. This swarm of structures, predominantly oriented NNE-SSW, spans approximately 160 km in length and up to 17 km in width. [NC1] This study focuses on exploring surface deformation dynamics induced by dyke intrusions in a specific area of the FFS, characterized by a volcanic cone and an asymmetrical central graben.

The volcanic cone under study is situated in the central-western part of the system and features a well-defined graben bordered by two major faults trending NNE-SSW, parallel to the cone maximum elongation axis. The cone measures approximately 3 km in length and 1.3 km in width, with an elongated shape consistent with the fracture orientation of the FFS. Geological mapping indicates that the cone is primarily composed of pillow lavas, hyaloclastites, and tuff from the latter half of the last glacial period. At its base, it contacts more recent lava flows, and scoria cones aligned parallel to the NNE-SSW direction are present on its western flank.

This study employs a multidisciplinary approach integrating advanced survey techniques, structural analysis, and numerical modelling. In situ data were acquired via aerial photogrammetry using drones and the MapIT app for georeferenced photos, enhancing lithological and structural characterization. Drone imagery was processed in Agisoft Metashape to produce a high-resolution 3D and 2D dataset, including an orthomosaic and a Digital Surface Model (DSM), providing a robust foundation for detailed geological structural analysis using GIS. This allowed for the identification of key structures and the measurement of fault offsets to analyse their relationship with the graben geometry.

Additionally, 2D numerical models were developed using the FEM software Comsol Multiphysics to investigate stress distribution and orientation at the dyke tip. These models explore the effect of factors such as dyke depth and inclination, Young’s modulus of the host rock, and topographical influences. Outputs show the distribution of tensile and von Mises stresses, the greatest compressive stress (σ1) and the least principal stress (σ3) to assess the relationship between the dyke intrusion and surface deformation. These models are ongoing, with results to be refined as additional data becomes available.