Surface fractures generated during the 2021 Reykjanes oblique rifting event (SW Iceland)

• Published in: Bulletin of Volcanology
• Main Authors: Bufféral, Simon, Panza, Elisabetta, Mannini, Stefano, Hjartardóttir, Ásta Rut, Nobile, Adriano, Gies, Nils, Óskarsson, Birgir Vilhelm, Ruch, Joël
• Other Authors: Physical Science and Engineering (PSE) Division, Department of Earth Sciences, University of Geneva, Geneva, Switzerland, Laboratoire de Géologie, École Normale Supérieure, PSL, Paris, France, Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland, Icelandic Institute of Natural History, Reykjavík, Iceland, Institute of Geological Sciences, University of Bern, Bern, Switzerland
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Springer Science and Business Media LLC 2023
• Subjects: Iceland
• Online Access: http://hdl.handle.net/10754/695462; https://doi.org/10.1007/s00445-023-01666-9

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. The authors would like to thank the Icelandic Civil Protection for the fruitful discussions that were held during the crisis, the University of Iceland (especially Páll Einarsson) for their availability on and off the field, Loftmyndir ehf. (loftmyndir.is) for the communication of their aerial images, and Andrew Harris, Emanuela De Beni and an ...