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The Buncefield Explosion: A benchmark for infrasound analysis in Europe

The Buncefield Explosion: A benchmark for infrasound analysis in Europe L. Ceranna, D. Green, A. Le Pichon & P. Mialle. BGR / B3.11, Hannover, Germany. AWE, Blacknest, United Kingdom. CEA/DASE, Bruyères-le-Châtel, France. www.flickr.com. Content. Infrasound recordings

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The Buncefield Explosion: A benchmark for infrasound analysis in Europe

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  1. The Buncefield Explosion: A benchmark for infrasound analysis in Europe L. Ceranna, D. Green, A. Le Pichon & P. Mialle BGR / B3.11, Hannover, Germany AWE, Blacknest, United Kingdom CEA/DASE, Bruyères-le-Châtel, France

  2. www.flickr.com Content • Infrasound recordings • Propagation modeling • Objectives • Conclusions • PMCC analysis in the frequency range between 0.1 and 4 Hz • Extraction of mean features: signal and wave parameters • Empirical wind model HWM-93 • Semi-empirical wind model NRL-G2S • 1-D / 3-D ray tracing – propagation tables • Comparing atmospheric models and propagation tools • Explain multiple arrivals and lack of detection at some stations • Source location with / without wind corrections • Single station location • Yield estimate • Explaining fast arrivals

  3. www.flickr.com The Buncefield Explosion 11-Dec-2005 06:01:32 (UTC) 51.78° N / 0.43° W (source: BGS) Hemel Hempstead, 40 km north of London vapor cloud blew up (~80,000 m2 and 1 to 7 m thick, ~300 t) ‘only‘ 43 people injured further explosions at 06:26 & 06:27 generated infrasound recorded all over central Europe

  4. Recordings of Infrasonic Arrivals

  5. Infrasound recordings at Flers: 334 km duration: 310 seconds, number of phases: 4 ▼ microbarometer seismometer

  6. Infrasound recordings at IGADE: 641 km duration: 397 seconds, number of phases: 5 ▼

  7. Infrasound recordings at I26DE: 1057 km duration: 644 seconds, number of phases: 6 ▼ microbarometer seismometer

  8. Infrasound recordings at UPPSALA: 1438 km duration: 454 seconds, number of phases: 5 ▼

  9. Infrasound recordings at LYCKSELE: 1806 km ▼ NO DETECTION

  10. Infrasound recordings at JAMTON: 2033 km ▼ NO DETECTION

  11. ▼ Infrasound recordings at KIRUNA: 2114 km NO DETECTION

  12. m/s m/s +60 m/s +20 m/s -50 m/s -20 m/s 25° HWM-93 wind model, 11-December-2005 06:00 (UTC) radial wind speed @ 10 km radial wind speed @ 40 km

  13. m/s m/s -130 m/s -30 m/s ▲ ▲ +90 m/s 30 m/s NRL-G2S wind model, 11-December-2005 06:00 UTC radial wind speed @ 10 km radial wind speed @ 40 km

  14. Differences caused by the extreme wind conditions • large differences in wind speed between HWM-93/NRL-G2S (20-70 m/s) • tropospheric winds blow in different direction • reception of Iw/Is to the SW/SE of London, predicted for NRL-G2S • maximum differences in wind speed between individual receivers: • ~20 m/s @ 10 km; ~60 m/s @ 40 km  Need for 3-D propagation simulations

  15. Phase Identification, e.g., Flers ray tracing (1-D τ-p) & WASP-3D phase identification using travel-time curves … and time-frequency analysis

  16. δβ=-1.6° δβ=1.2° δβ=2.5° δβ=-2.1° δβ=1.3° δβ=-0.5° Interpretation / Extracting main features – HWM-93

  17. δβ=0.5° δβ=-3.5° δβ=5.5° δβ=-0.2° δβ=5.8° δβ=0.8° δβ=7.5° δβ=-0.5° δβ=-5.0° δβ=7.5° δβ=-0.4° δβ=2.5° δβ=12° δβ=0° δβ=6.5° δβ=0.2° δβ=-13.5° δβ=0.5° Interpretation / Extracting mean signatures – NRL-G2S

  18. Location Results (I)

  19. Location Results (II)

  20. Single Station Location, Flers • average 1-D profile (d ~ number of Is phases * 200 km) along average β • 1-D travel-time curves • 2-D grid-search (celerity and Δ), calculating Trms → [Δ, torig, δβ] • next iteration …..

  21. Single Station Location, I26DE • N observations • M travel-time curves at Δ • origin time:

  22. Yield estimate [Whitaker et al., 2003; Evers et al. 2007] yield varies between 19 and 153 t HE 300 t vapor cloud → ~30 t HE

  23. Synthetic barograms – CPSM, NRL-G2S 2-D effective sound speed profiles Iw Δ=5.8° IGADE Is (Is)2 (Is)4 (Is)6 (Is)3 (Is)5 Iw Δ=9.5° I26DE (Is)2 (Is)4 (Is)5 (Is)6 (Is)7 (Is)8 (Is)9 (Is)10 (Is)11 Is (Is)3 Iw Δ=3.0° Flers (Is)2 It Is

  24. 400 600 800 1000 1200 [km] 200 Acoustic wave propagation, CPSM 2-D effective sound speed profiles Δ=5.8° IGADE 45 min Δ=9.5° I26DE 78 min Δ=3.0° Flers 25 min

  25. Conclusions I • The Buncefield Explosion was detected at almost all infrasound stations in central Europe • Signals from this explosion were also detected at 49 seismic stations as air-to-ground coupled waves. • All recordings are multi-phase signals (e.g. 6 phases at I26DE !!) • Data analysis and interpretation are demanding due to interfering signals with almost identical back-azimuths (Δβ < 7°) • microbaroms from the North Atlantic at German station I26DE • unknown arrivals directing to the English Channel • No signal detected in northern Sweden (Lycksele, Jämtön, Kiruna) although Is phases are predicted by HWM-93 • Propagation simulations and ray tracing based on HWM-93 provide an extremely poor correlation between recorded and theoretical data, therefore, the obtained localization results show a large deviation from the ground truth

  26. Conclusions II • Comparison between HWM-93 and NRL-G2S reveals large differences in the wind field with respect to speed (up to ± 80 m/s) as well as lateral heterogeneity (~60 m/s max) • Turning heights of It phases directed to station east of the source are >140 km, therefore, these phases are unlikely at I26DE, IGADE and Uppsala • Unusual atmospheric conditions: wide ranges of celerity for Is (250-290 m/s); up to 300 m/s for It • 3-D propagation tools are essential to solve problem of phase identification and calculate propagation tables • WASP 3-D ray tracer, Chebyshev pseudo-spectral wave propagation simulations, and NRL-G2S profiles, allowed to identify and label all recorded phases

  27. Conclusions III • wealth of data (infrasound arrivals at both seismic and dedicated infrasound arrays) was used to analyze systematically location accuracy • set of parameter: back-azimuth, travel-time, propagation path • station distribution • homogeneous azimuthal distribution of recording receivers is dominant pre-requisite for highly accurate location results, irrespective of the model • single station location was also performed achieving reasonable results • Chebyshev pseudo-spectral wave propagation simulations using NRL-G2S profiles allowed to identify and label all recorded phases, even the fast arrivals at IGADE and Flers • due to the extreme wind conditions and the strength of the source double branching of Is phases was observed • yield estimate was performed showing a large variation between 19 and 153 t TNT-equivalent

  28. Acknowledgement • We thank: • IRF, the Swedish Institute Space Physics for providing the infrasound waveform data from the stations in Uppsala, Lycksele, Jämtön, and Kiruna • D. Drob for providing NRL-G2S profiles • C. Millet (CEA/DASE) for simulations • L. Evers (KNMI) and R. Whitaker (LANL) for discussions

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