Relatively relocated seismicity during the 2021 Fagradalsfjall dyke intrusion, Reykjanes Peninsula, Iceland: Detailed evolution of a lateral dyke, and comparison to Bárðarbunga-Holuhraun
- 1University of Cambridge, Department of Earth Sciences
- 2Iceland GeoSurvey, Kópavogur, Iceland
- 3University of Iceland
- 4Charles University
- 5Institute of Geophysics, Prague
- 6Columbia University
- 7Institute of Geosciences, University of Potsdam
The 2021 Fagradalsfjall eruption on Iceland’s Reykjanes Peninsula was preceded by more than 12 months of elevated seismic and inflationary activity, beginning around December 2019. On 24th February 2021, an exceptionally intense episode of seismicity covering the length of the Peninsula marked the initiation of a dyke intrusion, which continued to develop until the 19th of March 2021, when melt first erupted at the surface. During the intrusion, more than 80,000 microearthquakes marked the propagation of melt, first northeast towards Mt Keilir, then to the southwest, eventually forming a 10 km-long dyke. These events were recorded by a dense local seismic network and detected and located using QuakeMigrate[1].
We present relative relocations of the seismicity, and tightly constrained focal mechanisms for earthquakes from the dyke intrusion period. The high precision of the relative relocations reveals fine scale structure in the region, which is studied in relation to the orientation of fault planes rupturing in individual earthquakes, thus providing insight into the mechanism of dyke propagation and the controls on faulting in the region. We find that the strikes of the fault planes of individual earthquakes differ from the overall trend of dyke propagation across several propagating seismic swarms.
We compare our findings for the Fagradalsfjall seismicity to the 2014-2015 Bárðarbunga-Holuhraun intrusion and eruption seismicity [2], in the context of the contrasting tectonic settings, and markedly different precursory activity.
1: Tom Winder, Conor Bacon, Jonathan D. Smith, Thomas S. Hudson, Julian Drew, & Robert S. White. (2021). QuakeMigrate v1.0.0 (v1.0.0). Zenodo. https://doi.org/10.5281/zenodo.4442749
2: Woods, J., Winder, T., White, R. S., and Brandsdóttir, B., 2019. Evolution of a lateral dike intrusion revealed by relatively-relocated dike-induced earthquakes: The 2014–15 Bárðarbunga–Holuhraun rifting event, Iceland. https://doi.org/10.1016/j.epsl.2018.10.032
How to cite: Glastonbury-Southern, E., Winder, T., Greenfield, T., Ágústsdóttir, T., Rawlinson, N., White, R., Brandsdóttir, B., Fischer, T., Horálek, J., Doubravová, J., Bacon, C., Gudnason, E. Á., Hersir, G. P., Hrubcova, P., and Eibl, E. P. S.: Relatively relocated seismicity during the 2021 Fagradalsfjall dyke intrusion, Reykjanes Peninsula, Iceland: Detailed evolution of a lateral dyke, and comparison to Bárðarbunga-Holuhraun, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8196, https://doi.org/10.5194/egusphere-egu23-8196, 2023.
