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Characterization of explosion signals from Tungurahua Volcano, Ecuador

This study analyzes explosion signals from Tungurahua Volcano in Ecuador using infrasound and seismic data, providing insights into the dynamics and evolution of explosions. The study also explores the correlation between explosion energy and volcanic activity.

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Characterization of explosion signals from Tungurahua Volcano, Ecuador

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  1. Characterization of explosion signals from Tungurahua Volcano, Ecuador David Fee and Milton Garces Infrasound Laboratory Univ. of Hawaii, Manoa dfee@isla.hawaii.edu Robin Matoza Laboratory for Atmospheric Acoustics (L2A) Scripps Institution of Oceanography

  2. Overview • Tungurahua Volcano • Array(s) • Explosion Algorithm and Events • Examples • March 2007 Sequence • May 2006 • Explosions Source • Cross-Correlation • Conclusions

  3. Tungurahua Volcano • 5023 m high, 3200 m of relief • Frequent eruptions characterized by pyroclastic flows, lavas, lahars, as well as tephra falls • Over 30,000 people live in close proximity, evacuated in 1999 • Significant ash ejections resulting from nearly constant tremor and explosions • Motivation: • Understand dynamics and evolution of explosions • Aid general understanding and monitoring Images Courtesy Instituto Geofisico

  4. ASHE Arrays - RIOE • 4 Element Array, ~100 m aperture • Chaparral 2 Microphones • Flat between 0.1-200 Hz • Collocated BB seismometer • Porous hoses in open field • Recorded signals from Tungurahua and Sangay Volcanoes 37 km 33° 43 km 132°

  5. Explosion Detection Algorithm • Time period: 2/15/06-11/1/2007 • High-pass filter data >.5 Hz • STA/LTA  event onset and end time • 2/5 secs, 3/40 secs • Detection must be on all 4 channels • Run PMCC between 0.5-4 Hz • 10 bands, 10 sec windows • Families with correct azimuth (±7°) during event time • Minimum RMS amplitude >0.02 Pa RMS • Minimum family size >15 pixels

  6. 4/1/06 4/1/06 7/1/06 7/1/06 10/1/06 10/1/06 1/1/07 1/1/07 4/1/07 4/1/07 7/1/06 7/1/06 10/1/06 10/1/06 Amplitude and Number Events • 9331 Events detected • >400 per day during peak • Events clumped during periods of high activity • Amplitudes: 0 .018-24.4 Pa Mean = 0.64 Pa • Durations: 0.1-16.5 s Mean = 3.95 s

  7. Acoustic Source Energy • EAcoustic=2πr2/ρc ∫ΔP(t)2dt r=source-receiver distance ρ=air density C=sound speed ΔP=change in pressure • Energy normalized by reference event • Removes geometric spreading and topographical effects • Reference Event: 1.30x107 J • Assume spherical spreading • More energy  more eruptive material?

  8. 4/1/06 4/1/06 7/1/06 7/1/06 10/1/06 10/1/06 1/1/07 1/1/07 4/1/07 4/1/07 7/1/06 7/1/06 10/1/06 10/1/06 Energy Release • Energy ratios: 7.5x10-5-502 Mean = 0.81 Largest explosions follow 7/14/06 VEI 3 Eruption • Group eruptive activity: • Background tremor • May 06 • July 14-15th, 2006 • August 16-17th, 2006 • March 07

  9. 4/1/06 7/1/06 10/1/06 1/1/07 4/1/07 7/1/06 10/1/06 Effective Yield • Convert Explosion Energies to Effective Yield • 1 ton of TNT = 4.184 GJ • Largest explosion=1.56 ton, most around .001 ton (~1 kg of TNT) • Volcanic explosion in fluid, relationship may not hold

  10. March 2007 Sequence - Example • Moderate-High Activity resumed between 2/15-4/15 • Significant number of explosions and associated ash • Seismic Tremor and LPs returned 2/23/07 • Significant number of explosions starting 2/24

  11. February 24th Event • 2/24/07 • Impulsive Onset • Signal lasts ~5 mins • Sustained amplitude ~± 1 Pa • Ash >40’000 ft • Jetting? Similar spectrum

  12. Acoustic Source Energy Example Explosion: 3/8/07 0745 UTC ~10 Pa at 36.89 km 368,900 Pa at 1 m  205 dB (re 20 μPa)! Effective Yield: 0.115 ton (105 kg) TNT

  13. March 2007 Explosion Energy • Most energetic explosions during middle of sequence • Cloudy weather hampered visual monitoring for much of sequence • Energy and number of explosions correlate well with heightened volcanic activity

  14. Observation vs. Recording: April 4th, 2007 • Good recording and viewing conditions. Selected day for eyewitness, satellite, infrasound correlations • Observation: 0450 UTC Explosion. Vibration of windows in Banos (7 km) and heard at observatory (13 km). Clear weather and constant emission reaching 8.5 km asl (~28,000 ft) • Infrasound: 2007-04-04 04:51:03, 2.91 Pa, 6.4 sec, 1.571 energy ratio

  15. Explosions  Infrasonic Harmonic Tremor • Mid-May 06: Explosions trigger gliding harmonics lasting up to 30 mins • Very little ash during these explosions/tremor • New Injection of Magma?

  16. Explosions  Seismic Harmonic Tremor • Band-limited sustained seismic tremor • Similar frequencies, but harmonics not very apparent (low SNR as well)

  17. Explosion Source • Ruiz et al. 2005: analyzed travel times of seismic and acoustic first arrivals (ΔT =Tacoustic-Tseismic) • Large variations in ΔT  source location variability? • Concluded explosions events originate <200m, followed by outflux of gas, ash, and solid material ~1 s later • May 06 Explosions similar to acoustic recordings from Arenal Volcano, Costa Rica (Garces et al., 98) • Explosion in low sound speed, low density magma-gas mixture would couple better into the atmosphere  acoustic impedance match • Then decompression front propagates into conduit and create resonance • Substantial pressure perturbation could destabilize the melt and initiate flow • Explosion near surface of a gas-rich conduit creates a resonance that transmits into the atmosphere and couples into earth through the conduit walls

  18. 2006/7/31 Explosion ~300 m Infrared Video 0.1 0 -0.1 • Somewhat emergent onset, relatively low amplitude • Long duration • Liquid magma ejected

  19. Cross-Correlation • Pick “master” waveform for subset of events • Cross-correlation for each event • Look at evolution of correlation value? • Parameters: 0.1-5 Hz, Window: -3 s, +8 s from onset, amplitude >.5 Pa Test Master Waveform

  20. Cross-Correlation Results • Subset data between 5/11-5/16 2006 • 385 Explosions • Waveforms very similar on 5/14 Master

  21. Cross-Correlation – Families • 37 km away so atmosphere effects may affect waveform similarity • Possible solution: compare waveforms with similar atmospheric conditions • Use 0.02-.1 Hz as a proxy for wind speed (Fee and Garces, 2007) • Sort explosions by waveform similarities (Green and Neuberg, 2006; Umakoshi et al., 2003) 5/11 Waveform Family 5/14 Waveform Family

  22. Conclusions • Significant number of high s/n explosions recorded from Tungurahua Volcano • Similarities and differences exist: amplitude, duration, energy, correlation, ash content, harmonics • Other data sources necessary to understand effect of explosions • Some ash rich, some ash poor • Understanding explosions key to hazard monitoring and dynamics at Tungurahua • Future Work • Correlate explosions with observed activity: ash, pyroclastic flows, incandescent blocks • Waveform cross-correlation by families: group by correlation and similar atmospheric conditions • Model acoustic/seismic explosion source and determine how it relates to tremor

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