Earthquake frequency-magnitude distribution at Mount Etna sheds light on magma ascent in the volcano’s plumbing system

Active volcanoes in densely populated areas are generally monitored through geological observations, geophysical, and geochemical data, which provide information on magma movement in the uppermost crust, allowing only short-term predictions of volcanic activity. However, deep magma recharge processes remain poorly understood. Here, we show that temporal variations in the slope of earthquake frequency-magnitude distribution (b value) at Mount Etna, a proxy for crustal stress changes, can track magma movements from deep to shallow crustal levels. Analyzing two decades of seismicity (2005–2024) across three crustal sectors, we distinguished magma recharge from the mantle, its transfer and storage at intermediate depths, and final ascent to the surface. Moreover, we found that b value time variations can precede geochemical anomalies from magma ascent and its eruption by a few months. Our results suggest that b value monitoring could have anticipated volcanic crises, supporting its integration into multiparametric surveillance systems for medium and long-term volcano monitoring.