Search

We use a comprehensive dataset of field observations, high spatial resolution drone orthomosaics and digital terrain models (DTMs) to map, quantify and characterize the extensive ground fracturing related to the 2021 seismo-tectonic and volcanic activity in the Reykjanes Peninsula (Iceland). The dataset, spans an area of about 30 km 2 , where we map nearly 20 000 ground cracks with metric to decametric lengths and centimetric extensional offsets, revealing a dominant dextral shear, in agreement with published seismic data. Although striking in a direction similar to the volcanic systems in the Reykjanes Peninsula (N030–040), most fractures appear as en-échelon structures globally aligned along N-S-striking fault zones up to 3–4 km long. By examining the timing of ground fracturing through repeated field observations, seismic data and InSAR images, we associate a fracture zone with most earthquakes of M ω ≥ 5.0 that occurred in the month preceding the March 2021 Fagradalsfjall eruption. We describe three preexisting N-S fault zones, with fault segments that were reactivated up to three times during the pre-eruptive seismic activity, while the magma intrusion did not trigger graben-related ground fractures typically observed during magmatic injections. Our depiction of a system dominated by strike-slip tectonic features helps in understanding the geometry and bookshelf-mode of tectonic activity along a diffuse and highly oblique extensional plate boundary. Evidence of transient fracturing is typically quickly lost because of erosion or lava flow burial, highlighting a potential under-representation of diffuse fracturing when studying old tectonic and volcanic systems. [ABSTRACT FROM AUTHOR]

Rift obliquity is known to be very frequent at divergent plate boundaries and shear components in the opening of fissures have been detected through seismicity in the monitoring of recent rifting events. However, the field structural evidence of obliquity in active rifts for Holocene events is still poorly studied, despite its relevance at both the lithospheric and upper-crust scales. We performed extensive high resolution UAV surveys on Holocene terrains in four areas along the active rift in the Northern Volcanic Zone of Iceland, to map structures and morphotectonic features in detail. We did a kinematic analysis and found an increase of the obliquity from N to S. We further discuss the origins of this obliquity and suggest that the combination of inherited structures reactivation, magmatic intrusions, and topography influence on the propagation of both fractures and magma intrusions can have an impact on the mismatch between rift opening direction and the far-field strain. We conclude that obliquity can be inferred for Holocene rifting events from surface structural data. It is thus fundamental to take into account the existing structural pattern and its (re)activation history in active rift zones to avoid missing out on possible preferential structure reactivation, magma propagation ways, and eruption sites during the monitoring of ongoing rifting events. • Holocene rifting obliquity in Iceland inferred from surface structural field data. • UAV surveys for extensive and high-resolution structural analysis. • Morphotectonic analysis to infer faults and graben reactivation and dike intrusions. [ABSTRACT FROM AUTHOR]