Autor Ckelar: Luis Lara.
Otros autores: Luis Franco-Marín, Daniel Basualto, José Luis Palma, Fernando Gil-Cruz, Carlos Cardona y Cristian Farias.
Revista científica: Volcanology and Geothermal Research
Abstract
Llaima Volcano (38.692°S, 71.729°W) is one of the most active centers in South America, with ∼56 eruptions since 1852 CE. During the last eruptive cycle (2007–2009), the volcano displayed typical features of open conduit systems, with frequent long-period volcanic seismicity (LP). After the MW 8.8 Maule megathrust earthquake (27 February 2010), Llaima volcano located 305 km to SE of the epicenter, has experienced one of the longest periods of quiescence since 1852, with reduced activity observed since the beginning of its continuous instrumental monitoring in the year 2007. To better understand this behavior, we track the repose time between eruptions in the 20th century to depict the current period of quiescence and provide details of the pattern of volcano seismicity after the earthquake. The number of LP events decreased ∼90% shortly after the earthquake. In turn, crustal faults nearby (∼20 km south of the main crater) showed an increased level of seismicity lasting for approximately six months after the mainshock before returning to background levels. In order to propose driving mechanisms for such behavior, we computed the static changes of the stress tensor on chosen receiver structures. The acting receiver structure differs from those related to the long-term stress regime controlled by regional tectonics and was inferred from the pre-earthquake shallow seismicity (2007–2009). LP and volcanotectonic seismicity (VT) before the earthquake were located in a NW-SE pattern, in contrast to the NE-trending alignment of flank vents (and hence dike swarms) usually interpreted as an indicator of the maximum horizontal stress axis. From the static stress transfer imparted by the earthquake, we find that an opening event would have occurred at a NW-trending receiver structure coupled with closing of other potential structures, which promoted magma storage along this blind structure but precluding further propagation to the surface. Our results thus show a rare example of earthquake-induced suppression of volcanic activity, where the geometry of the fault-fracture network that shape the plumbing system likely plays a major role.
Full paper here.