In the last two decades, an increasing interest for infrasound observations of volcanic eruptions has been shared by several scientific communities thanks to the development of the worldwide Infrasound Network, part of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT).
Volcanic eruptions are processes in which magmatic fluids equilibria is restored from the induced perturbations caused by its rise in a chamber deep in the crust. When a volcano erupts, it releases energy in the form of pressure waves into the atmosphere, and the term infrasound is referred to acoustic waves with frequencies below the audible range of human hearing (~<20 Hz). There is a variety of eruptive styles, and each one produces unique and different infrasound signals, most commonly related to a) tremor; b) extrusion rate; c) eruptive column; and d) degassing (e.g. Marchetti et al., 2009; Johnson & Ripepe, 2011; Chouet & Matoza, 2013, Fee & Matoza, 2013, 2018). Once the infrasonic pressure field may be directly associated with the flux rate of gas released, it promotes an extra efficient tool for volcanic monitoring.
Whereas at a local scale, recent infrasound studies from active volcanoes have allowed successful advances in volcanic hazards mitigation related to eruption dynamics within the context of monitoring and in the understanding of volcanic source parameters (e.g., Vergniolle & Brandeis, 1994; Ripepe et al., 2001; Ripepe & Marchetti, 2002; Dabrowa et al., 2011; Fee et al., 2013), at regional or global scale it still very uncertain the contribution of infrasound signals associated to volcanic activity on a near real-time monitoring (Dabrowa et al., 2011).
The IMS infrasound network is nowadays composed by 53 certified infrasound stations (on March 1st, 2021). Aiming at detecting and locating atmospheric and underground nuclear explosions down to 1 ton of TNT (1kT) at any point on the globe, is the only global monitoring network of its kind (Christie & Campus, 2010). Given its mandate for detecting nuclear explosions, the IMS Infrasound Network has demonstrated its potential to locate and characterize natural and anthropogenic events (Christie & Campus, 2010).
The Instituto de Investigação em Vulcanologia e Avaliação de Riscos (IVAR) operates an infrasound station (IS42) located in Graciosa island, which integrates the IMS that operationalise the verification regime of the Comprehensive Test-Ban Treaty (CTBT).
The use of infrasound has become a well-established research technic providing a valuable working tool for monitoring volcanic activity, both in the near- and far-field. The challenges of infrasound monitoring lie in the detection of signals, the determination of source locations and the estimation of source parameters, and each of these aspects depend critically on infrasonic wave propagation through the atmosphere.
The work presented in this thesis aims at demonstrating the possibility to perform near real-time long-range monitoring of erupting volcanoes based on IMS stations data.