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Copahue volcano straddling the edge of the Agrio‐Caviahue caldera along the Chile‐Argentina border in the southern Andes has been in unrest since inflation began in late 2011. We constrain Copahue's source models with satellite and airborne interferometric synthetic aperture radar (InSAR) deformation observations. InSAR time series from descending track RADARSAT‐2 and COSMO‐SkyMed data span the entire inflation period from 2011 to 2016, with their initially high rates of 12 and 15 cm/yr, respectively, slowing only slightly despite ongoing small eruptions through 2016. InSAR ascending and descending track time series for the 2013–2016 time period constrain a two‐source compound dislocation model, with a rate of volume increase of 13 × 106 m3/yr. They consist of a shallow, near‐vertical, elongated source centered at 2.5 km beneath the summit and a deeper, shallowly plunging source centered at 7 km depth connecting the shallow source to the deeper caldera. The deeper source is located directly beneath the volcano tectonic seismicity with the lower bounds of the seismicity parallel to the plunge of the deep source. InSAR time series also show normal fault offsets on the NE flank Copahue faults. Coulomb stress change calculations for right‐lateral strike slip (RLSS), thrust, and normal receiver faults show positive values in the north caldera for both RLSS and normal faults, suggesting that northward trending seismicity and Copahue fault motion within the caldera are caused by the modeled sources. Together, the InSAR‐constrained source model and the seismicity suggest a deep conduit or transfer zone where magma moves from the central caldera to Copahue's upper edifice.

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Since the reactivation of Galeras volcano in 1988 its seismic activity has been dominated by a variety of LP waveforms and tremor events. Some of these signals occurred as a response to volcanic activity. Among them, two kinds of tremor deserve special attention, Flute tremor and Spasmodic tremor. Flute tremor has a spectrum of equally spaced peaks and is associated with a quasi-steady degassing process at the top of the lava dome. It is accompanied by a flute-like sound. Its spectral features and the correlation with field observations are consistent with a model generation indicating that a crack or set of cracks are excited to resonance by the release and flow of gas through the lava dome. Spasmodic tremor is composed of several distinct LP-like events joined together by a continuous signal with lower amplitudes. Two types of spasmodic tremor may be distinguished on the basis of their spectral characteristics and field observations. Spasmodic tremor type I is apparently dominated by a mix of P, SH and Rayleigh waves as determined from preliminary polarization analysis. The source appears to be located, in a region west of the active crater. As a first approximation, Spasmodic tremor type I could be associated with magmatic intrusion process occurred in 1989-1991.

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 event. We present the first systematic characterization of near-field seismicity associated with a large high-silica eruption analyzing data recorded before, during and after the 4 June 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, the time series of the b value and the computation of the 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, and 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, and changes in eruptive style and waning phases of eruptions, with broader implications for monitoring and forecast of violent silicic eruptions.