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This study focuses on real-time localization of infrasound signals from Italian volcanoes, specifically Stromboli and Etna. The study analyzes the seismic and infrasonic signals to infer source dynamics within the shallow plumbing system of the volcanoes.
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Real-time infrasound localization on active Italian volcanoes E. Marchetti, M. Ripepe, G.Ulivieri and G. Lacanna Dipartimento di Scienze della Terra, Università di Firenze, Italy
multi vents systems Infrasonic arrays monitoring Italian Volcanoes Stromboli: 2003 - present Etna: 2006 - present
explosions Sample of infrasound: Stromboli gas bursting
gas bursting - ~1-20 Pa at 500 m from the source - recurrence time of ~ 2 sec Sample of infrasound: Stromboli explosions - ~10-100 Pa at 500 m from the source -10-20 events/hour
Real-Time Source Location: - background Near source array deployment (spherical wave propagation NO PLANE WAVE) Large signal-to-noise ratio - requirements Fast computing time High spatial resolution Real-time visualisation of the source position and evaluation of excess pressure at the source - procedure Grid searching with assumption: plane at fixed elevation spherical propagation in an homogeneous medium
1. Grid definition 2. time shift between records, assuming constant velocity 3. semblance between pairs of record 4. semblance across the array Filtering out non-volcanic phenomena Real-Time Source Location: grid searching:
Real-Time Source Location: Real-Time Array Processing
Real-Time Source Location: grid searching, Etna 19 Oct 2006_23:26:45 Map of Semblance Distribution and BackAzimuth Direction
FDTD model Topography into account assuming: perfectly reflecting surface modeled with stair stepping • - no wind • homogeneous atmosphere • no attenuation • cell 5x5 m • pressure at 10 m from the surface • source in air at 25 m from the surface
Located source Theoretical pressure waves Good azimuthal resolution The fixed-plane and homogeneous medium assumptions do not affect the result FDTD model Source position
1° Real-Time Source Location: grid searching, Etna 19 Oct 2006_22:48:45 Map of Semblance Distribution Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 19 Oct 2006_22:49:30 24° Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 19 Oct 2006_22:53:10 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 19 Oct 2006_23:01:55 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 19 Oct 2006_23:03:50 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 20 Oct 2006_23:48:10 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 22 Sept 2006_23:03:50 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 19 Oct 2006_23:26:45 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 20 Oct 2006_23:01:20 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 22 Sept 2006_11:18:25 Map of Semblance Distribution and BackAzimuth Direction
Real-Time Source Location: grid searching, Etna 22 Sept 2006_11:15:25 Map of Semblance Distribution and BackAzimuth Direction
7 1 -10 24 Real-Time Source Location: grid searching, Etna 217000 infrasonic transients located in 58 days • Infrasonic Amplitude and - propagation back-azimuth of infrasonic sources
back-azimuth of infrasound released Sept. 09 - Nov. 6, 2006 SE NE VG BN # transients located ~ 217,000
300° 290° 280° 270° 260° 250° Real-Time Source Location: azimuth scanning, Stromboli Semblance Distribution Jan, 31, 2004 12:00-21:00
gas bursting explosions > Bubbly flow at bifurcations? - Drops are travelling along branches with high Flux - Whenever Flux Changes, Drops change their path Flux Manga, J. Fluid Mech., 1996 infrasonic back-azimuth - Gas bursting stable form hours to days - Degassing changes abruptly from vent to vent
2003 2004 NE C # detections ~ 4 millions # detections ~ 5 millions 2005 2006 NE C C # detections ~ 6.5 millions # detections ~ 3 millions Changes in volcanic activity: 2003-2006
log-log excess-pressure distribution of infrasonic transients: 2003 - 2006 degassing explosions gas bursting and explosions are not produced by a scale-invariant process: Evidence for a Different Dynamics?
Polarization of VLP seismic transients Source Location of different active vents Stromboli May 7-8, 2006
Source Location of different active vents Diapositiva 30 Stromboli May 7-8, 2006
comparison of stacked ground displacement Different vents are associated with significantly different seismic and infrasonic signals
conclusions • efficiency of infrasound arrays describing activity at multi vents volcanoes, and inferring source dynamics withing the shallow plumbing system • SIMPLE & FAST Real-time source location based on semblance across the array • grid-searching / azimuth-scanning at fixed propagation velocity Fast computing time and filter for non-volcanic processes • Array analysis --> how and when single vents are active (monitoring - research)