Geophysical Classification of Strombolian Explosive eruption

Transcription

1 Geophysical Classification of Strombolian Explosive eruption Ripepe M. and E. Marchetti Department of Earth Sciences, University of Firenze, Firenze - Italy Monitoring Centre for Civil Protection - Italian Ministry of the Interiors

2 Explosive Activity of Stromboli Puffing Height <10 1 m Ordinary Height ~10 2 m Major Height <10 3 m Paroxysm Height >10 3 m

3 Fallout dispersal, Mass and Volume 05/4/ /3/2007 Mass 05/04/2003 = ~10 8 kg 15/03/2007 = ~10 7 kg Majors (Rosi et al., 2008) (Pistolesi et al., 2011) = ~10 6 kg (Andronico & Pistolesi, 2008) Ordinary = ~10 3 kg (Ripepe et al., 1993) (Harris et al., 2013) Volume 05/04/2003 = ~10 5 m 3 15/03/2007 = ~10 4 m 3 Majors = <10 3 m 3 Ordinary = ~10 0 m 3 Mass and Volume Ejected can span Five orders of magnitude

4 Height (m) Mass Discharge Rate of Strombolian Activity /03/2007 5/04/ /03/2007 Majors Mass Discharge Rate 5 April = ~10 7 kg/s 15 March = ~10 6 kg/s Majors = ~10 5 kg/s Ordinary = ~10 3 kg/s Puffing = ~10 0 kg/s 10 2 Ordinary H = 0.25 Q 0.38 Puffing Mass Flux (Kg/s) H = 2 Q Mastin et al., 2009 Mass Discharge Rate scales with the plume height and ranges SEVEN order of magnitude

5 VEI VEI of Strombolian Activity 5/04/ /03/ /03/2007 Majors Volumetric Discharge Rate 5 April = ~10 3 m 3 /s 15 March = ~10 2 m 3 /s Majors = ~10 1 m 3 /s Ordinary = ~10 0 m 3 /s Puffing = ~10-3 m 3 /s Ordinary Considering: VEI = log(q) Puffing Volumetric Flux (m 3 /s) 10 7 Assuming a DRE volumetric flux Strombolian activity ranges between VEI =0 and 3

6 Integrated Geophysical Network 5 Seismic broad-band (30s) Guralp CMG40T + 5 infrasonic microphones ( Hz) 2 Thermal Radiometers (9-14µ) OMEGA OS 3 Tiltmeters Pinnacle 5000T res. 1 nrad at 1sps 2 Thermal Cameras FLIR A10 1 Infrasonic Array 1 Buoy - Tide Gauge and Hydro-acoustic

7 Integrated Geophysical Network 5 Seismic broad-band (30s) Guralp CMG40T + 5 infrasonic microphones ( Hz) 2 Thermal Radiometers (9-14µ) OMEGA OS 3 Tiltmeters Pinnacle 5000T res. 1 nrad at 1sps 2 Thermal Cameras FLIR A10 1 Infrasonic Array 1 Buoy - Tide Gauge and Hydro-acoustic

8 Geophysical parameters monitored seismic seismic VLP infrasound explosion onset thermal Infrasound and Thermal Camera can help to constraint seismic source

9 Amplitude Variability of seismic VLP VLP amplitude Low amplitude VLP High amplitude VLP

10 Amplitude Variability of seismic VLP ~10-5 m VLP amplitude shows a three order of magnitude variation

11 Distribution of Seismic VLP Amplitude ~ events ( ) 1.2x10-5 m 0.6x10-5 1x x x10-5 4x10-5 Seismic VLP amplitude shows a threshold at 1.2x10-5 m

12 Pressure (Pa) Pressure (Pa) Pressure (Pa) Variability of Infrasonic Pressure Puffing ~2 Pa Ordinary Activity ~20 Pa Major Explosions ~200 Pa time (sec) Infrasonic Waveform is Stable but Amplitude ranges two orders

13 Distribution of Acoustic Pressure 100 Pa ~ events ( ) Infrasonic Pressure shows a threshold at ~100 Pa

14 Ground deformation Seismic VLP signal Ground Tilt

15 Ground Deformation Induced by Explosive Dynamics Stacked Inflation/Deflation ~ 1000 Events a ~150 s b c a,b) Ground inflation controlled by magma rise and diffusive bubble growth. 1.5 (Nishimura, JVGR, 2009) t µ t a b c ~ s c) Ground deflation following explosion acted by conduit contraction and reaction force. Inflation Starts ~150 s before Explosions (Genco & Ripepe, 2010)

16 Ordinary Activity, Major Explosion and Paroxysm Paroxysm 15 March 2007 Stacking of 23 Major Explosions Stacking of 1000 Ordinary Explosions time (s) Deformation Spans Two Orders of Magnitude

17 Inflation rate for ordinary, majors and paroxysm Ordinary Major Paroxysm ~300 s before explosive onset Same Inflation Rate: Sharing the same Dynamics! Implications for Early Warning System

18 Distribution of ground tilt ~ events ( ) 0,25 mrad Ground Tilt shows a threshold at ~0.25 mrad

19 Tilt (mrad) Correlation between Seismic and Tilt UD (mm) 0 Dec Jan Feb Mar Apr 0 Ground Tilt is well correlated to Seismic VLP Amplitude

20 Log Distribution of Seismic, Pressure and Tilt Ordinary activity & major explosions since Dec. 2008

21 Log Distribution of Seismic, Pressure and Tilt 30-June-2010 Major explosions are clearly above the Ordinary activity threshold

22 Ground Tilt (mrad) VLP seismic amplitude and Ground Tilt VLP seismic amplitude and Ground Tilt µrad major 15/03/07 05/04/03 paroxysms ordinary 10-5 m Ground displacement (m) EGU, 10 April 2013, Vienna, Austria

23 Ground Tilt (mrad) VLP seismic amplitude and Ground Tilt VLP seismic amplitude and Ground Tilt µrad major energy gap? 15/03/07 05/04/03 paroxysms ordinary 10-5 m Ground displacement (m) EGU, 10 April 2013, Vienna, Austria Is this GAP reflecting a different dynamics? or it is only matter of time!!

24 Conclusive Remarks - Strombolian activity spans 7 order of magnitude in terms of mass ejected and mass discharge rate - Major Explosions can be defined on the base of seismic, ground deformation and acoustic pressure. - Ground Tilt indicates that Strombolian Activity is characterized by a persistent Inflation/Deflation Cycle - Inflation Rate is Compatible with a deformation controlled by magma rise and diffusive bubble growth. - Ground Inflation starts ~350 s before the Explosive Onset and could be used as Early Warning Parameter - Geophysical Parameters evidence a Gap in the Intensity between Major Explosions and Paroxysms.