Realtime infrasound localization on active Italian volcanoes E

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

Infrasonic arrays monitoring Italian Volcanoes multi vents systems Stromboli: 2003 - present Etna: 2006 - present

Sample of infrasound: Stromboli explosions gas bursting

Sample of infrasound: Stromboli explosions - ~10 -100 Pa at 500 m from the source -10 -20 events/hour gas bursting - ~1 -20 Pa at 500 m from the source - recurrence time of ~ 2 sec

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

Real-Time Source Location: 1. Grid definition grid searching: 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: Real-Time Array Processing

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

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

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

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

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

Real-Time Source Location: grid searching, Etna 19 Oct 2006_22: 53: 10 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 19 Oct 2006_23: 01: 55 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 19 Oct 2006_23: 03: 50 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 20 Oct 2006_23: 48: 10 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 22 Sept 2006_23: 03: 50 Map of Semblance Distribution and Back. Azimuth Direction

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

Real-Time Source Location: grid searching, Etna 20 Oct 2006_23: 01: 20 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 22 Sept 2006_11: 18: 25 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 22 Sept 2006_11: 15: 25 Map of Semblance Distribution and Back. Azimuth Direction

Real-Time Source Location: grid searching, Etna 217000 infrasonic transients located in 58 days 7 1 -10 24 - 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

Real-Time Source Location: grid searching, Stromboli

Real-Time Source Location: azimuth scanning, Stromboli 300° 290° 280° 270° Semblance Distribution 260° 250° Jan, 31, 2004 12: 00 -21: 00

infrasonic back-azimuth gas bursting explosions - Gas bursting stable form hours to days - Degassing changes abruptly from vent to vent > 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

Changes in volcanic activity: 2003 -2006 NE 2003 2004 C # detections ~ 5 millions # detections ~ 4 millions 2005 2006 NE C # detections ~ 3 millions C # detections ~ 6. 5 millions

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?

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

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

comparison of typical infrasonic transients

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 - research) (monitoring

FDTD: infrasound propagation