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

Abstract

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 4th 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.

Decoding the state of stress and fluid pathways along the Andean Southern Volcanic Zone

“…The time window of short-term data represents the period of recorded seismicity by local seismic networks. The relative age of fault slip data was taken from literature [16][17][18][19][20][21][24][25][26][27][28][29][30][31][32][33][34][35][36] , and mostly ranges from Miocene to Quaternary. They are considered maximum faulting ages because they are defined from the rock unit(s) they crosscut.…”

“…1. For individual volcanoes, we calculated both the short-and longterm stress state from focal mechanisms and FSD [16][17][18][19][20][21][24][25][26][27][28][29][30][31][32][33][34][35][36] . The raw seismological and structural database can be found in the Supplementary Note S1, Supplementary Data 1, Supplementary Table 1, and in an online repository declared in Data availability.…”

“…Earthquake magnitudes range from Mw 1.0 to 4.1, and fault slip data include a wide range of fault sizes, from millimeters to meters. Each component of the database employed here has already been collected, discussed, and published in previous works [16][17][18][19][20][21][24][25][26][27][28][29][30][31][32][33][34][35][36] , but here they are analyzed holistically to understand the tectonomagmatic processes occurring in the SVZ rather than in individual volcanoes only. To build our database we only considered volcanoes with existing seismic and/or field data within a conservative radius of 2 kilometers from the volcanic edifice or located in major faults spatially associated with volcanoes.…”

“…In total, we conducted seven short-term [16][17][18][19][20][21] and thirteen longterm [24][25][26][27][28][29][30][31][32][33][34][35][36] analyses, accounting for 23% of the volcanoes within the SVZ, that include 16 different volcanic complexes (i.e., 12 polygenetic volcanoes and 4 monogenetic volcanic fields; Figs. 1, 2).…”

Perceptions of past and future eruptions of Puyehue-Cordón Caulle (Southern Chile): connecting neighbourhood, social cohesion and disaster memory in volcanic risk research

“…The most recent eruptions of PCCVC occurred in 1921PCCVC occurred in -1922PCCVC occurred in , 1960PCCVC occurred in , and 2011PCCVC occurred in -2012. The 2011 eruption was the largest among the PCCVC historical eruptions (Basualto, 2019;Seropian et al, 2021). It had severe transboundary impacts on the ecosystem, economy, transportation, tourism, agriculture, and critical infrastructure at a regional scale (Elissondo et al, 2015).…”