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Increasing seismic activity within the intraplate volcanic system of Ljósufjöll in Western Iceland.

Jóhanna Malen Skúladóttir 1, Páll Einarsson2, Halldór Geirsson2, Gregory Paul De Pascale2, Vincent Drouin1, Tom Winder2, Benedikt Ófeigsson1, Kristín Jónsdóttir1, Kristín Vogfjörð1, Helga Ívarsdóttir1, Sara Barsotti1

  • Affiliations: 1Icelandic Meteorological Office, Reykjavík, Iceland; 2Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland

  • Presentation type: Poster

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

  • Poster Board Number: 138

  • Programme No: 2.1.48

  • Theme 2 > Session 1

Abstract

A significant increase in earthquake activity was noted in 2021 in a tight cluster within the Ljósufjöll volcanic system, one of three volcanic systems of the Snæfellsnes Volcanic Zone in Western Iceland. The activity continued at a similar rate in 2022 and 2023 but increased in August 2024, with the largest event, of magnitude 3.2, recorded on December 18th 2024. The hypocentral depths of the earthquakes are 15-20 km. Most of the located earthquakes are typical volcano-tectonic events, with high frequency and clear S-waves. They are likely caused by brittle fracturing of rocks. They do occur, however, at considerable depth below the typical brittle-ductile transition for usual tectonic strain rates, which in Iceland is normally at 6-10 km depth. The earthquakes occur in an area of minimal tectonic strain rate within the North American Plate. Magma movements are therefore the most likely cause of brittle fracturing at this depth. Bursts of continuous tremor were detected in the area in December 2024-January 2025, further strengthening the interpretation of magmatic origin of the activity. Events located within these bursts are at similar depths as before. As of January 2025, no surface deformation has been detected in the area. Previous activity resembling this earthquake sequence include seismicity accompanying the 1973 Heimaey eruption and the deep dike intrusion at Upptyppingar, north of Vatnajökull, in 2007-2008. The latest eruption in the Ljósufjöll Volcanic System occurred in the tenth century CE. The monitoring effort has been increased in the area with additional seismic and GNSS instruments.