Deformation and seismicity decline before the 2021 Fagradalsfjall eruption

Area of Science:

• Geophysics
• Volcanology
• Tectonics

Background:

• Volcanic eruptions are often preceded by increased ground deformation and seismicity as magma ascends.
• Pre-eruptive patterns of deformation and seismicity show significant variability.
• Understanding these patterns is crucial for effective volcanic eruption forecasting.

Purpose of the Study:

• To analyze the pre-eruptive deformation and seismicity patterns of the 2021 Fagradalsfjall eruption in Iceland.
• To investigate the role of tectonic stress release in modulating volcanic unrest.
• To improve eruption forecasting models by incorporating complex volcanic-tectonic interactions.

Main Methods:

• Analysis of geodetic data for ground displacement.
• Seismic monitoring to track earthquake activity and magnitudes.
• Geological modeling to understand magma dyke emplacement and stress dynamics.

Main Results:

• The Fagradalsfjall eruption was preceded by significant magma dyke emplacement (9 km long, ~34x10^6 m^3 volume) and strike-slip earthquakes up to M_W 5.64.
• A period of declining deformation and seismicity occurred days before the eruption, linked to tectonic stress release.
• Shallowing magma depth and potentially weaker shallow crust may have influenced seismicity patterns.

Conclusions:

• Tectonic stress release can significantly influence pre-eruptive deformation and seismicity, leading to temporary decreases.
• Volcanic eruption forecasting must consider the interplay between magmatic processes and regional tectonic stress.
• Crustal layering and its interaction with magma emplacement are critical factors in understanding volcanic unrest.