The 2025 Santorini unrest unveiled: Rebounding magmatic dike intrusion with triggered seismicity

Magmatic intrusion in Earth's crust can lead to hazardous volcanic eruptions, but the physical processes involved remain largely hidden from direct observation. We used machine learning-derived seismicity as virtual stress meters at depth to study the disruptive 2025 seismogeodetic unrest in Greece between the Santorini volcano and the epicenter of the devastating moment magnitude 7.7 Amorgos earthquake that occurred in 1956. We show that the cause of unrest was magmatic dike propagation, which we imaged with ~25,000 relocated earthquakes occurring over 2 months. The dike propagated horizontally ~30 kilometers as multiscale rebounding waves of dike opening, magma pressure, and breaking of barriers while triggering intense surrounding seismicity. Our results establish magmatic intrusion as a more complex feedback process than previously recognized and can facilitate physics-based and data-driven modeling and eruption forecasting.