2025 Santorini-Amorgos crisis triggered by a transition from volcanic to regular tectonic activity

Fluid movement beneath volcanic regions can influence earthquake activity, but the processes linking seismic and volcanic systems are not fully understood. In early 2025, an unusual seismic sequence occurred close to Santorini, providing new insight into these interactions. Here we show that the sequence was likely initiated by the accumulation and migration of fluids beneath the volcanic complex. Seismic and ground deformation data reveal a progression from deep fluid buildup and microfracturing to the concentration of shallow earthquakes beneath Columbo volcano. This culminated in a four-day seismic episode that behaved like a single, slow-propagating rupture along a 16-kilometer fault, releasing energy equivalent to a magnitude 6.2 earthquake. The rupture was followed by a typical aftershock sequence. These observations suggest that fluid-driven processes can generate large earthquakes and redistribute stress in ways similar to tectonic mainshocks. This challenges conventional views on how seismic and volcanic hazards are connected and assessed.