Potential for rupture before eruption at Campi Flegrei caldera, Southern Italy

Volcanoes reawakening after long repose must rupture the crust before magma can erupt. Rupture is preceded by repeatable variations in the rate of seismicity with ground movement, which trace the amount of applied stress that is released by local earthquakes. A rupturing sequence has been developing across four episodes of ground uplift at Italy’s Campi Flegrei caldera: in 1950-1952, 1969-1972, 1982-1984 and since 2004. We predicted in 2016 that the approach to rupture would continue after an additional uplift of 30-40 cm at the location of largest movement. We have updated our analysis with new data on changes in the numbers of local earthquakes with amounts of ground movement. Here we show that subsequent events have confirmed our prediction and that the unrest has been changing the structure of Campi Flegrei’s crust. The results provide new constraints for evaluating the volcano’s potential to erupt or to subside without eruption.