Investigating the subsurface drivers of the 2025 Kolumbo volcano-tectonic unrest

At active volcanoes, surface deformation and seismicity reflect underlying processes related to regional tectonics as well as the storage and movement of magma and fluids. These processes frequently overlap, complicating efforts to distinguish between magmatically, hydrothermally, and tectonically driven volcanic unrest. As a result, interpreting unrest signals remains a major challenge in volcanology, particularly if geophysical and geodetical observations are not integrated with physics-based models. In this study, we investigate the subsurface processes that may account for the pulsating seismicity observed along a ~30km-long NE-SW-trending structure during the 2025 Santorini-Amorgos (Greece) earthquake crisis, using physics-based, time-dependent Finite Element Method (FEM) models. Specifically, we simulate crustal extension and poroelastic deformation driven by magmatic and/or hydrothermal pressure sources. Our preliminary results show that the pulsating seismic patterns observed during the seismic crisis may have been controlled by a transient poroelastic response of the shallow crust to the transport of volatiles from a deep magma reservoir to the surface. Numerical simulations show that the sudden pressurization of leaky magma reservoirs, which release fluids through permeable pathways, generates cyclic and laterally migrating zones of tensile stress within a depth-dependent, highly fractured elastic crust. This dynamic response contrasts with the more localized and static stress accumulation produced by the pressurization of sealed magma reservoirs, thus underscoring the critical role of fluid migration in controlling the spatial and temporal evolution of seismicity during volcanic unrest. Integrating fluid–rock coupling into models of fluid transport and crustal pressurization offers a pathway toward more reliable interpretation of unrest signals and improved volcanic hazard assessments.