Extensional Tectonics and Magma-Driven Seismicity Across the Santorini–Amorgos Basins, South-Central Aegean Sea: Insights from the 2025 Earthquake Swarm

Summary

We examined source characteristics of the recent earthquake sequence that occurred in February 2025 between the volcanic fields of Santorini, Kolumbo, Anydros, and Amorgos in south-central Aegean. This region lies within the volcanic back-arc domain of the Hellenic subduction zone in the Aegean Sea. During this period, the area experienced intense seismic activity (ten earthquakes 5.0 < Mw < 5.5), with earthquake magnitudes generally increasing towards Amorgos Island. The largest event was the Mw 5.4 earthquake on 10 February 2025, located northeast of Santorini. In this study, we first obtained 4,869 earthquakes that occurred between 2 January 2024 and 23 March 2025. We then derived full moment-tensor (MT) solutions for 30 earthquakes (Mw ≥ 4.5) by inverting seismological datasets. In addition, principal stress orientations were calculated by stress tensor inversion to recognize the most recent crustal stress field in the region. The spatio-temporal distribution of the relocated aftershocks indicates that the seismic activity initiated beneath the Santorini and Kolumbo volcanic centers, and subsequently migrated northeastward towards Anydros and Amorgos. Most earthquakes occurred at shallow crustal depths of approximately 5–15 km. Stress-inversion results and the orientation of T-axes highlight a dominant NW–SE extensional regime that characterizes the combined effects of deep geodynamic processes and shallow crustal dynamics in the back-arc area of the Aegean. The full MT solutions reveal predominantly normal, oblique-normal, and strike-slip faulting mechanisms, accompanied by significant non-double-couple (non-DC) components. These non-DC signatures strongly suggest tensile processes that are likely related to magma intrusion, fluid migration, or hydraulic fracturing. We therefore conclude that the 2025 seismic sequence was largely driven by crack-opening mechanisms and fluid- or magma-induced activity within the crust, consistent with the broader structural framework and volcanic nature of the Santorini–Amorgos region. Overall, this study enhances our knowledge on tectonic characteristics of the 2025 Santorini-Amorgos earthquake activity, which is significant for evaluating and monitoring the potential hazards in the south-central Aegean region.