Eruption time series statistically examined: Probabilities of future eruptions in the Chilean Southern Volcanic Zone

The Chilean Southern Volcanic Zone (SVZ) is the volcanologically most active part of the Chilean Andes, hosting the very active Llaima and Villarrica Volcanoes and more than 60 large volcanic edifices. The high population density, industrial and agricultural use, and touristic attractiveness of the region calls for volcanic hazard assessment for these hazard-exposed zones. Continuous monitoring of seismic activity, gas release and composition, ground deformation, scientific constraints on regional tectonics and geochemistry, etc., is the most powerful tool for assessing the current state of a volcano. Recent efforts by the Chilean OVDAS have greatly improved the coverage by the installation of a large number of seismometers on the Chilean volcanoes considered as most active. Although not developed to substitute monitoring efforts, statistical analysis of eruption time series has advanced to become an important component of hazard assessment, providing the tool for probabilistic eruption forecasting. In the ideal case of surveyed volcanoes, it complements the investigation of interacting geophysical, volcanological and geochemical processes. At the numerous volcanoes where no permanent monitoring data are available, it presents the only approach to estimating eruption likelihood. Moreover, it provides an estimate of the hazard posed by a volcano encompassing a longer time scale, independently of its present state of activity. These empirical approaches use methods borrowed from standard life distribution/failure analyses usually applied in engineering or medical contexts. Here we present an overview of the statistical methods employed to eruption time series for the Chilean SVZ volcanoes, aiming at characterizing the volcanoes' eruptive hazard