Deep long period seismicity preceding and during the 2021 Fagradalsfjall eruption, Iceland

Abstract

We use a dense seismic network on the Reykjanes Peninsula, Iceland, to image a group of earthquakes at 10–12 km depth, 2 km north-east of 2021 Fagradalsfjall eruption site. These deep earthquakes have a lower frequency content compared to earthquakes located in the upper, brittle crust and are similar to deep long period (DLP) seismicity observed at other volcanoes in Iceland and around the world. We observed several swarms of DLP earthquakes between the start of the study period (June 2020) and the initiation of the 3-week-long dyke intrusion that preceded the eruption in March 2021. During the eruption, DLP earthquake swarms returned 1 km SW of their original location during periods when the discharge rate or fountaining style of the eruption changed. The DLP seismicity is therefore likely to be linked to the magma plumbing system beneath Fagradalsfjall. However, the DLP seismicity occurred ~ 5 km shallower than where petrological modelling places the near-Moho magma storage region in which the Fagradalsfjall lava was stored. We suggest that the DLP seismicity was triggered by the exsolution of CO2-rich fluids or the movement of magma at a barrier to the transport of melt in the lower crust. Increased flux through the magma plumbing system during the eruption likely adds to the complexity of the melt migration process, thus causing further DLP seismicity, despite a contemporaneous magma channel to the surface.

Illuminating the Transition From an Open to a Semi‐Closed Volcanic Vent System Through Episodic Tremor Duration and Shape

“…Greenfield et al. (2022) reported a deep long period (DLP) event swarm in late June and in July 2021 that is aligned with the transition to hour‐long episodes. These DLP events could indicate changes in CO 2 ‐rich fluids or the movement of magma about 5 km above the Moho in the same time window.…”

Lava flow hazard modeling during the 2021 Fagradalsfjall eruption, Iceland: applications of MrLavaLoba

“…Illustration of the temporal development of the volcanic unrest (column 1), the simulations performed addressing these developments (column 2), the identified simulation challenges (column 3), the modifications implemented to address these challenges (column 4) and the remaining challenges. Sigmundsson et al, 2022;Greenfield et al, 2022;Barsotti et al, 2023). On 24 February 2021, an intense earthquake swarm began with an M w 5.64, located 2-4 km northeast of Fagradalsfjall, marking the start of a dike intrusion.…”

Insights on the state of stress in the mantle beneath Pahala, Hawai‘i

“…A growing body of work suggests that magmatic activity at lower crustal and mantle depths can influence eruptive behavior at the surface over relatively short timescales (e.g. days to months) [Shapiro et al 2017;Cesca et al 2020;Feuillet et al 2021;Greenfield et al 2022]. This behavior has been observed at volcanoes in a variety of tectonic settings and suggests a high degree of hydraulic connectivity between deep (10-35 km) and near-surface melt reservoirs.…”