Reactivating and Calming Volcanoes: The 2015M(W)8.3 Illapel Megathrust Strike

The 2015M(W)8.3 Illapel earthquake was followed in a time frame of weeks to months by very different responses from Nevados de Chillan, Copahue, and Villarrica volcanoes, all located more than 580 km from the rupture zone. Here we show how Nevados de Chillan and Copahue started new eruptive phases, and Villarrica entered in a period of relative calm. Using seismic, geodetic, and geochemical observations, in combination with numerical wave propagation simulations, we also show that the geometry of the fault system controlled the impact of the earthquake on each volcano. We argue that the sensitivity of a volcano toward an earthquake depends on both its critical state before the mainshock and the geometry of its fault system. This is a case where the same earthquake generates very different responses at the same time, at large distances, rendering volcanoes as very sensitive systems.

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