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Repeated dike injections beneath the Sundhnúkur crater row, Reykjanes Peninsula, Iceland, imaged by relatively relocated seismicity

Tom Winder1, Elías Rafn Heimisson1, Thorbjörg Ágústsdóttir2, Egill Árni Gudnason2, Bryndís Brandsdóttir1, Nick Rawlinson3, Jan Burjánek4, Jana Doubravová4, Tomáš Fischer5, Pavla Hrubcová4, Kristín Jónsdóttir6, Eva P. S. Eibl7

  • Affiliations: 1Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland; 2Iceland GeoSurvey (ÍSOR), Reykjavík, Iceland; 3Department of Earth Sciences, University of Cambridge, Cambridge, UK; 4Institute of Geophysics, Czech Academy of Sciences, Prague, Czechia; 5Charles University, Faculty of Science, Prague, Czechia; 6Icelandic Meteorological Office, Reykjavík, Iceland; 7Institute of Geosciences, University of Potsdam, Potsdam, Germany 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 117

  • Programme No: 2.1.27

  • Theme 2 > Session 1

Abstract

Between November 2023 -- January 2025 there have been eight dike intrusions and seven fissure eruptions beneath Sundhnúkur, on the Reykjanes Peninsula, Iceland. Geodetic and geochemical analyses show that these have been fed by a common source, located at 3-4 km depth beneath the harnessed Svartsengi geothermal area. This remarkable sequence of magmatic activity has been marked by abundant seismicity. Relative quiescence on the Peninsula following the July-August 2023 Fagradalsfjall eruption was interrupted in late October by elevated seismicity and surface uplift measured at Svartsengi, 8 km further west. As during inflation episodes at Svartsengi in 2020 and 2022, intense shallow seismicity accompanied the deformation, dominantly consisting of strike-slip faulting above an inferred sill. From around 15:00 on 10th November 2023, intense migrating seismicity and rapid metre-scale horizontal deformation marked the intrusion of a NNE-SSW oriented dike, which reached approximately 15 km length in just 8 hours, and propagated under the town of Grindavík, which was evacuated. On 18th December, similar (though smaller amplitude) signals marked a second, smaller intrusion, but in contrast this dike quickly breached the surface and culminated in a 4 km long fissure eruption. A similar pattern has repeated in the following 12 months, with cyclical re-inflation beneath Svartsengi, and repeated dike intrusions and fissure eruptions along a common lineament. Through analysis of high-resolution relative relocations of the dike-induced seismicity, we investigate the relative geometry of the repeated dike intrusions, and the relationship between the seismicity and distribution of dike opening and location of eruption onset.