Anatomy of a High-Silica Eruption as Observed by a Local Seismic Network: The June 2011 Puyehue-Cordón Caulle Event (Southern Andes, Chile)

Abstract. High-silica explosive eruptions are one of the most dangerous natural phenomena, yet it is unclear which processes are involved in this infrequent kind of events. We present the first systematic characterization of near-field seismicity associated to a large high-silica eruption analyzing data recorded before, during and after the June 4^th 2011 rhyolitic eruption of Puyehue Cordón Caulle Volcanic Complex (PCCVC). Results of a first-level data processing, developed by The Southern Andean Volcano Observatory (OVDAS) to monitor unrest and the evolution of the eruption, are complemented here with the relocation of hypocenters into a local 1D velocity model, time-series of the b-value and the computation of focal mechanism. This information allows us to define several phases before and after the onset of the eruption, describing details of the space-time evolution of seismicity, defining and characterizing the seismic sources, identifying the structural-control of the magmatic intrusion and stress variations during the eruption. Our results illuminate several underlying processes, with emphasis on the possible role that basement structures had on the storage, transport and evacuation of magma. Integrating our results with previous findings based on satellite geodesy and petrology of erupted materials, we discuss general conceptual models regarding destabilization of structurally-controlled acidic magmatic systems, the pass from unrest to eruption, changes in eruptive style and waning phases of eruptions, with broader implications for monitoring and forecast of violent silicic eruptions.