INFRASOUND

The Laboratory of Experimental Geophysics is studying for more than 20 years to studying infrasound, compressional wave at low frequency (<20 Hz) that propagate into the atmosphere. The infrasonic waves are produced from natural and anthropogenic sources that disturb the atmosphere, such as explosions, the mass flows , waves or earthquakes, and have the ability to propagate in a very efficient wa , up to thousands of miles from the the source.
Since 1990, the Laboratory of Experimental Geophysics infrasound has applied to the study of volcanic explosions , especially on the Stromboli volcano (ME), and then widen the scope of investigation to mining activities in the quarry, and more recently to the study of gravity waves to the study of the atmosphere and the identification and study of avalanches and pyroclastic flows.
Over the years, the Laboratory has refined analytical procedures and data processing infrasonic particularly with the use of infrasound arrays that enable noise reduction and a reduction of the ambiguity of the investigation, and has made extensive use infrasound as a means of real-time monitoring of volcanic explosions and avalanches.
The research carried out by the laboratory in the field of infrasound has led to the development of algorithms analysis of arrays, for spherical wavefronts and plans, and the design and development of arrays and infrasonic
sensors.

Volcanic activity

Volcanoes emit infrasound whenever gas pressure and / or materials are emitted into the atmosphere during explosive activity or outgassing. This parameter provides information estremamete important, being a direct expression of erupted material , which combined with other geophysical parameters can provide a more complete picture of the dynamic process that produces volcanic eruptions.
The Laboratory has developed research infrasonic sound of the volcano Stromboli in the early 80s and now operates an integrated network that consists of 5 stations and an array of 5 elements in the summit area. This allows continuous monitoring and dattagliato of infrasonic and over the years has led to the detection and localization of over 10 million discrete explosive events and degassing. The detections of individual infrasonic transients are made through the array. Here coherent signal to the various elements of the array is identified by the function semblance and events are localized in real time via an algorithm developed due to spherical wavefronts [ Ripepe and Marchetti , 2002; Ripepe et al. , 2007 ]. This analysis procedure allows to follow in detail the evolution of infrasonic, both in terms of over- pressure of localization.
In addition to the instrumentation installed at Stromboli Laboratory manages the permanent infrasonic arrays on volcanoes Etna, Soufriere Hills - Montserrat, West Indies (in collaboration with the Montserrat Volcano Observatori ), Asama - Japan (in collaboration with the Earthquake Research Institute) and Eyjafjallajökull - Iceland (in collaboration with the University of Reykjavik). Temporary measurement campaigns were carried out on volcanoes Kilauea (Hawaii), Villarrica (Chile) and Yasur (Vanuatu).

Mining activity

The Laboratory of Experimental Geophysics played seismo- acoustic measurement campaigns in different basins Tuscan extraction , aimed at the study seismic- acoustic coupling of the various activities of the outbreak , and the monitoring and planning of the activities of the quarry.

In this area, infrasonic arrays are an effective tool to detect and characterize uniquely mining endogenous with respect to noise or to different anthropogenic sources . In addition, the ability to discriminate different sources allows the effective application of infrasound arrays in basins mining complex , where live different realities mining , providing a real-time assessment of mining activities and the consequent effects in each slot.
The Laboratory has conducted measurement campaigns temporary basins extraction of Campiglia Marittima (LI) and Firenzuola (FI), through the installation of a seismic- acoustic array, equipped with a seismic sensor Lennartz triassilae 3D/5sec and an array of 4 infrasonic sensors PRS-100a with an aperture of 150 m.

 

Avalanche activity

The Laboratory of Geophysics Sperimetale conducted in the 2009-2010 winter season a pilot experiment of infrasonic noise in the upper Lys Valley (Aosta) in collaboration with AINEVA ( Interregional Association Snow and Avalanche ) and the Autonomous Region of Valle d' Aosta, through a 4-element infrasound array with an aperture of 150 meters and equipped with infrasonic sensors PRS-100a.
The experiment has allowed us to develop new algorithms coherent infrasonic signal detection as a function of the angle and elevation of the acoustic beam , and algorithms identidicazione and automatic extraction of the transients compatible with avalanche events , such as to provide a good operation the system automatically.
The analysis has allowed us to fully characterize the local avalanche activity within a radius of 5-10 km around the array, providing guidance on the time of occurrence, duration, and note the morphology and localization absolute energy and the path of the phenomena of detachment.

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