Stress transfer between volcanic dyke and seismic activity accompanying the 2021 and 2022 Fagradalsfjall eruptions, Iceland
- 1Charles University, Faculty of Science, Institute of Hydrogeology, Egineering Geology and Applied Geophysics, Prague, Czechia (fischer@natur.cuni.cz)
- 2Institute of Geophysics, Faculty of Science, Prague, Czechia
- 3Iceland GeoSurvey (ÍSOR), Reykjavik, Iceland
The 2021 Fagradalsfjall volcanic eruption in the Reykjanes Peninsula, Iceland, was preceded by an intensive earthquake swarm lasting one month. At the end of July 2022, a new intensive earthquake swarm occurred, which was followed on 3 August 2022 by a new effusive flow at the extension of the 2021 effusive fissure. We analyze seismic data of both swarms recorded by the Reykjanet local seismic network to trace the processes leading to the eruption to understand the relation between seismic activity and magma accumulation.
Precise relocations of the 2021 swarm show two hypocenter clusters in the depth range of 1-6 km. The WSW-ENE trending cluster of the 2021 and previous swarms show a stepover of ∼1 km offset, forming a pull-apart basin structure at the intersection with the dyke. This is the place where the 2021 eruption occurred, suggesting that magma erupted at the place of crustal weakening. The pre-eruption seismic activity in 2021 started with a ML 5.3 earthquake of 24 February 2021, which triggered the aftershocks on the oblique plate boundary and in the magmatic dyke area, in both cases in an area of elevated Coulomb stress. The co-existence of seismic and magmatic activity suggests that the past seismic activity weakened the crust in the eruption site area, where magma accumulated. The following ML 5.3 earthquake of 24 February 2021 also triggered the seismic swarm and likely perturbed the magma pocket which led to the six-months lasting eruption that started on 19 March.
The relocations of the July 2022 earthquake swarm show that only the northern part of the dyke-related swarm was activated compared to the 2021 swarm and both eruptions are located at the southern tip of the 2022 swarm. We compare the space-time and statistical characteristics of the 24 February 2021 aftershock sequence and of the 2021 and 2022 swarms to relate them to the different expected origin of these seismic activities.
How to cite: Fischer, T., Vlček, J., Hrubcová, P., Doubravová, J., Ágústsdóttir, Þ., and Guðnason, E. Á.: Stress transfer between volcanic dyke and seismic activity accompanying the 2021 and 2022 Fagradalsfjall eruptions, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16208, https://doi.org/10.5194/egusphere-egu23-16208, 2023.
