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

Stromboli: present Etna: present Infrasonic arrays monitoring Italian Volcanoes multi vents systems

gas bursting explosions Sample of infrasound: Stromboli

explosions - ~ Pa at 500 m from the source events/hour gas bursting - ~1-20 Pa at 500 m from the source - recurrence time of ~ 2 sec Sample of infrasound: Stromboli

- background Near source array deployment (spherical wave propagation NO PLANE WAVE) Large signal-to-noise ratio - procedure Grid searching with assumption: plane at fixed elevation spherical propagation in an homogeneous medium - requirements Fast computing time High spatial resolution Real-time visualisation of the source position and evaluation of excess pressure at the source Real-Time Source Location:

grid searching: Real-Time Source Location: Filtering out non-volcanic phenomena 1. Grid definition 2. time shift between records, assuming constant velocity 3. semblance between pairs of record 4. semblance across the array

Real-Time Array Processing Real-Time Source Location:

19 Oct 2006_23:26:45 Map of Semblance Distribution and BackAzimuth Direction Map of Semblance Distribution and BackAzimuth Direction Real-Time Source Location: grid searching, Etna

FDTD model - cell 5x5 m - pressure at 10 m from the surface - source in air at 25 m from the surface - no wind - homogeneous atmosphere - no attenuation Topography into account assuming: perfectly reflecting surface modeled with stair stepping

Source position Theoretical pressure waves Located source Good azimuthal resolution The fixed-plane and homogeneous medium assumptions do not affect the result FDTD model

Map of Semblance Distribution Map of Semblance Distribution 1° Map of Semblance Distribution and BackAzimuth Direction Map of Semblance Distribution and BackAzimuth Direction 19 Oct 2006_22:48:45 Real-Time Source Location: grid searching, Etna

24° 19 Oct 2006_22:49:30 Map of Semblance Distribution and BackAzimuth Direction 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 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 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 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 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 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 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 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 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 Map of Semblance Distribution and BackAzimuth Direction Real-Time Source Location: grid searching, Etna

infrasonic transients located in 58 days - Infrasonic Amplitude and - propagation back-azimuth of infrasonic sources Real-Time Source Location: grid searching, Etna

SE BN VG NE Sept Nov. 6, 2006 # transients located ~ 217,000 back-azimuth of infrasound released

Real-Time Source Location: grid searching, Stromboli

Semblance Distribution Jan, 31, :00-21:00 Real-Time Source Location: azimuth scanning, Stromboli 250° 270° 260° 280° 290° 300°

infrasonic back-azimuth gas bursting explosions - Gas bursting stable form hours to days - Degassing changes abruptly from vent to vent     >    Manga, J. Fluid Mech., 1996  Flux Bubbly flow at bifurcations? - Drops are travelling along branches with high Flux - Whenever Flux Changes, Drops change their path

Changes in volcanic activity: NE # detections ~ 5 millions 2005 C # detections ~ 3 millions 2006 C NE # detections ~ 6.5 millions 2004 C # detections ~ 4 millions

log-log excess-pressure distribution of infrasonic transients: degassing explosions gas bursting and explosions are not produced by a scale-invariant process: Evidence for a Different Dynamics?

Source Location of different active vents Stromboli May 7-8, 2006 Polarization of VLP seismic transients

Source Location of different active vents Stromboli May 7-8, 2006 Diapositiva 30

comparison of typical infrasonic transients

comparison of stacked ground displacement Different vents are associated with significantly different seismic and infrasonic signals

- 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) conclusions

FDTD: infrasound propagation