Seismo-magmatic interaction and stress evolution during the 2020–2024 Reykjanes Rift cycle, Iceland

Between 2020 and 2024, the Reykjanes Peninsula (Iceland) experienced a renewed phase of seismic and volcanic unrest after several centuries of relative quiescence. Four eruptive episodes occurred within the Fagradalsfjall–Sundhnúksgígar volcanic system, each associated with pronounced seismic swarms and significant changes in the spatial and temporal distribution of earthquake activity. In this study, we analyse the seismicity recorded during this period using a homogeneous earthquake catalogue provided by the Icelandic Met Office, with the aim of characterising the evolution of seismic activity in relation to the eruptive sequence. The results document systematic temporal variations in seismicity rate, cumulative seismic energy release, and b-value, as well as a progressive NE-ward migration of seismic clusters along the rift system. Seismicity evolves from relatively deep and spatially distributed activity to shallower and more localised fracturing in temporal proximity to eruptive onsets. While b-value decreases are not uniquely associated with eruptions, their temporal fluctuations are consistent with recurrent changes in the seismic regime during phases of volcanic unrest. The observed patterns are interpreted within the framework of previously published geophysical and geodetic studies, which indicate a multi-level magmatic plumbing system beneath the Reykjanes Peninsula. Our results suggest that seismicity provides indirect constraints on the evolving stress conditions and magma transport pathways during the 2020–2024 unrest, highlighting the strong interaction between tectonic extension and magmatic processes in an active rift environment. This study contributes to a refined seismological characterisation of rifting-related volcanic unrest and provides observational benchmarks for future multidisciplinary investigations of seismo-magmatic coupling.