Abstract
Volcanic eruptions are valuable calibrating sources of infrasonic waves worldwide detected by the International Monitoring System (IMS) of the Comprehensive Nuclear Test-Ban-Treaty Organization (CTBTO) and other experimental stations. In this study, we assess the detection capability of the European infrasound network to remotely detect the eruptive activity of Mount Etna. This well-instrumented volcano offers a unique opportunity to validate attenuation models using multi-year near-and far-field recordings. The seasonal trend in the number of detections of Etna at the IS48 IMS station (Tunisia) is correlated to fine temporal fluctuations of the stratospheric waveguide structure. This observed trend correlates well with the variation of the effective sound speed ratio which is a proxy for the combined effects of refraction due to sound speed gradients and advection due to along-path wind on infrasound propagation. Modeling results are consistent with the observed detection capability of the existing regional network. In summer, during the downwind season, a minimum detectable amplitude of ~10 Pa at a reference distance of 1 km from the source is predicted. In winter, when upwind propagation prevails, detection thresholds increase up to ~100 Pa. However, when adding four experimental arrays to the IMS network, the corresponding thresholds decrease down to ~20 Pa in winter. The simulation results provide here a realistic description of long- to mid-range infrasound propagation and allow predicting fine temporal fluctuations in the European infrasound network performance with potential application for civil aviation safety.
Highlights
A large variety of natural and anthropogenic phenomena produces intense low-frequency acoustic waves below the 20 Hz human hearing threshold [1]
A detailed analysis of the multi-year infrasound observations at IS48 confirms that the propagation of signals from Etna is essentially controlled by fine-scale temporal variations of the stratospheric waveguide structure
A frequencydependent modeling tool has been used to assess the performance of the European infrasound network to monitor its eruptive activity
Summary
A large variety of natural and anthropogenic phenomena produces intense low-frequency acoustic waves below the 20 Hz human hearing threshold [1] These signals, referred to as infrasound, can propagate over large distances through the atmosphere due to low attenuationin acoustic waveguides between the ground and troposphere, in the stratosphere and lower thermosphere [2,3,4,5]. Etna in Italy (37.73 ̊N, 15.00 ̊E; 3330 m high) is in Europe the highest and most active strato-volcano It is located on the east coast of Sicily, lying above the convergent plate margin between the African and the Eurasian plates. Since October 2010, more paroxysmal eruptive periods, characterized by strong Strombolian activity, lava fountaining, and often dense dark ash emissions were reported. Such information is not as precise as continuous near-field observations. We evaluate the performance of the existing IMS network and quantify its improvement by adding experimental stations
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