Quantifying the effect of large earthquakes in promoting eruptions due to stress changes on magma pathway: The Chile case

Four earthquakes with Mw≥8 occurred in proximity to 60 Holocene volcanoes, in the Southern Volcanic Zone of the Andes (SVZ) since 1906. We analyzed these events by numerical modeling and field data to understand the key attributes of each volcano that may lead to a seismically-triggered eruption and the general mechanisms by which earthquakes could trigger volcanic new activity. We developed a new approach by resolving the earthquake-induced normal static stress change on the magma pathway of each volcano instead of considering the general crustal volume. We also considered other parameters that may lead to eruption, such as magma chamber depth, magma composition and viscosity, local tectonic settings and volcano dimension. The dataset includes a total of 18 new volcanic activities following large earthquakes (15 eruptions and 3 minor increases in volcanic activity) at 10 volcanoes. Of these, 9 out of 18 events representing unrest occurred at volcanoes that had no activity in the five years before the earthquake. Results indicate that the static stress changes were capable of triggering the observed volcanic phenomena up to a distance of 353km from the epicenter. Eleven out of 18 new volcanic events occurred at volcanoes with shallow magma chambers (2-3km) under conditions of unclamping or very weak clamping. New activity at volcanoes with deeper magma chambers (>7km) occurred only by magma pathway unclamping. Considering the regional tectonics of the SVZ, 5 volcanoes lying along strike-slip faults, 3 on thrust faults and 2 along a transition zone, experienced unrest. Our results show that magma pathway unclamping plays a fundamental role in dictating unrest at volcanoes that are already in a critical state. These studies contribute to possible individuation of those volcanoes that are more prone to seismically-triggered eruptive events. © 2012 Elsevier B.V.