Uncertainty in Detection of Volcanic Activity Using Infrasound Arrays: Examples From Mt. Etna, Italy

SD and LZ acknowledge the support from the EUROVOLC project under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 731070). The authors thank the staff of the Istituto Nazionale di Geofisica e Vulcanologia Sezione di Catania, in particular Salvo Rapisarda, Daniele Pellegrino, Mario Pulvirenti, and Danilo Contrafatto for their valuable support in the field.The injection of gas and pyroclastic material from volcanic vents into the atmosphere is a prolific source of acoustic waves. Infrasound arrays offer efficient, cost-effective, and near real-time solutions to track the rate and intensity of surface activity at volcanoes. Here, we present a simple framework for the analysis of acoustic array data, based on least-squares beamforming, that allows to evaluate the direction and speed of propagation of acoustic waves between source and array. The algorithms include a new and computationally efficient approach for quantitative assessment of the uncertainty on array measurements based on error propagation theory. We apply the algorithms to new data collected by two 6-element infrasound arrays deployed at Mt. Etna during the period July–August 2019. Our results demonstrate that the use of two infrasound arrays allowed detecting and tracking acoustic sources from multiple craters and active vents associated with degassing and ash-rich explosions, vigorous and frequent Strombolian activity, opening of new eruptive fractures and emplacement of lava flows. Finally, we discuss the potential use of metrics based on infrasound array analyses to inform eruption monitoring operations and early warning at volcanoes characterized by episodic intensification of activity.NERC Natural Environment Research Council NE/P00105X/1European Union (EU)Geoscientists without Borders grant from the Society of Exploration Geophysic