Time-lapse monitoring of the unrest period of the Villarrica (or Ruka-Pillañ) volcano, Chile, occurred in 2015 from Coda-wave interferometry

Abstract

Coda-wave interferometry is an innovative monitoring tool to determine apparent velocity variations in (near) real-time usingcontinuous seismic data recorded by a network of seismic stations. As the scattered seismic waves are more sensitive to smallchanges occurring in the medium (Aki and Chouet, 1975; Weaver et al., 2011; Ermert et al., 2017), Coda-wave interferometry hasbeen widely applyed to monitor volcanic eruptions (Brenguier et al., 2008; Duputel et al., 2009; Mordret et al., 2010; Obermann et al.,2013; Sens-Schonfelder et al., 2014; De Plaen et al., 2016) and large magnitude earthquakes (Roux, 2009; Obermann et al., 2014),that may induce structural changes below the surface. Here, we analyse 14 months of seismic data (from April 2014 to June 2015)recorded by 10 broad-band seismometers deployed around the Villarrica volcano (i.e. < 40 km). By cross-correlating the verticalcomponent of daily seismic waveforms, we extract and stretch coherent Coda-waves for each station pair. Using the closeststations to the Villarrica volcano, we found consistent velocity variations (-2% < dv/v < 2%) that might be related with the periodof unrest between February and April in 2015. During this period of time, degassing processes and strombolian eruptions wereobserved at the volcano edifice (Aiuppa et al., 2017; Delgado et al., 2017). The main goal of this work is demotrate the potential ofCoda-wave interferometry as a useful tool to monitor and understand the dynamic of the activity observed at the Villarrica volcano.