1. Infrasound Technology Workshop – Tokyo, November 2007 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 CEA/DASE, Bruyères-le-Châtel, France AWE, Blacknest, United Kingdom

2. Infrasound Technology Workshop – Tokyo, November 2007 2 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 www.flickr.com

3. Infrasound Technology Workshop – Tokyo, November 2007 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 m 2 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. Infrasound Technology Workshop – Tokyo, November 2007 4 Recordings of Infrasonic Arrivals

5. Infrasound Technology Workshop – Tokyo, November 2007 5 Infrasound recordings at Flers: 334 km ▼ microbarometer seismometer duration: 310 seconds, number of phases: 4

6. Infrasound Technology Workshop – Tokyo, November 2007 6 Infrasound recordings at IGADE: 641 km ▼ duration: 397 seconds, number of phases: 5

7. Infrasound Technology Workshop – Tokyo, November 2007 7 Infrasound recordings at I26DE: 1057 km duration: 644 seconds, number of phases: 6 ▼ microbarometer seismometer

8. Infrasound Technology Workshop – Tokyo, November 2007 8 Infrasound recordings at UPPSALA: 1438 km ▼ duration: 454 seconds, number of phases: 5

9. Infrasound Technology Workshop – Tokyo, November 2007 9 Infrasound recordings at LYCKSELE: 1806 km ▼ NO DETECTION

10. Infrasound Technology Workshop – Tokyo, November 2007 10 Infrasound recordings at JAMTON: 2033 km ▼ NO DETECTION

11. Infrasound Technology Workshop – Tokyo, November 2007 11 Infrasound recordings at KIRUNA: 2114 km ▼ NO DETECTION

12. Infrasound Technology Workshop – Tokyo, November 2007 12 HWM-93 wind model, 11-December-2005 06:00 (UTC) radial wind speed @ 10 kmradial wind speed @ 40 km -20 m/s +20 m/s -50 m/s +60 m/s m/s 25°

13. Infrasound Technology Workshop – Tokyo, November 2007 13 NRL-G2S wind model, 11-December-2005 06:00 UTC radial wind speed @ 10 kmradial wind speed @ 40 km m/s 30 m/s -30 m/s -130 m/s +90 m/s ▲ ▲

14. Infrasound Technology Workshop – Tokyo, November 2007 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. Infrasound Technology Workshop – Tokyo, November 2007 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. Infrasound Technology Workshop – Tokyo, November 2007 16 Interpretation / Extracting main features – HWM-93 δβ=-0.5° δβ=-1.6° δβ=-2.1° δβ=2.5° δβ=1.2° δβ=1.3°

17. Infrasound Technology Workshop – Tokyo, November 2007 17 Interpretation / Extracting mean signatures – NRL-G2S δβ=0.5° δβ=-5.0° δβ=-13.5° δβ=0.2° δβ=5.5° δβ=12° δβ=-3.5° δβ=0° δβ=-0.4° δβ=-0.5° δβ=-0.2° δβ=0.5° δβ=7.5° δβ=5.8° δβ=7.5° δβ=0.8° δβ=2.5° δβ=6.5°

18. Infrasound Technology Workshop – Tokyo, November 2007 18 Location Results (I) Location ConfigurationLatitudeLongitudeOrigin time 11/12/05 Δd [km] Δt [s] ground truth51.78° N0.43° W06:01:31 Infrasound Array Data Only βno model1st51.24°N1.72°E-­161- multiple51.00°N1.54°E-162- HWM-931st51.61°N1.75°E-152- multiple51.40°N1.64°E-149- NRL-G2S1st51.65°N0.94°E-96- multiple51.89°N0.96°W-38- β & T I HWM-931st51.15°N0.71°E06:07:41114370 multiple51.05°N0.33°E06:05:3388242 NRL-G2S1st51.81°N0.96°W05:59:3037-121 multiple51.80°N0.24°W06:01:1813-13

19. Infrasound Technology Workshop – Tokyo, November 2007 19 Location Results (II) Location ConfigurationLatitudeLongitudeOrigin time 11/12/05 Δd [km] Δt [s] ground truth51.78° N0.43° W06:01:31 Coupled Seismic Arrivals Only T DS no model1st51.74°N0.41°W06:01:285-3 T DS & T SS no model1st51.68°N0.41°W06:01: 32111 Combined Infrasound Array Data & Coupled Seismic Arrivals β & T DS no model1st51.70°N0.95°W06:02:383767 β & T I & T DS & T SS NRL-G2S1st51.70°N0.35°W06:01:2410-7 multiple51.67°N0.40°W06:01:3012-2 Single Infrasound Array Data: Flers β & T I NRL-G2Smultiple51.72°N0.58°W06:01:33122 Single Infrasound Array Data: I26DE β & T I NRL-G2Smultiple51.97°N0.68°W06:00:1928-72

20. Infrasound Technology Workshop – Tokyo, November 2007 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 T rms → [Δ, t orig, δβ] next iteration …..

21. Infrasound Technology Workshop – Tokyo, November 2007 21 Single Station Location, I26DE N observations M travel-time curves at Δ origin time:

22. Infrasound Technology Workshop – Tokyo, November 2007 22 Yield estimate StationFlersIGADEI26DE V D [m/s]159195 A [Pa] max1.355.954.88 min0.453.871.67 P WCA [Pa] max0.730.140.10 min0.240.090.03 Y [t]max1535385 min322919 median--33 [Whitaker et al., 2003; Evers et al. 2007] yield varies between 19 and 153 t HE 300 t vapor cloud → ~30 t HE

23. Infrasound Technology Workshop – Tokyo, November 2007 23 Is (Is) 2 It Iw (Is) 4 (Is) 3 (Is) 6 (Is) 5 (Is) 11 (Is) 7 Iw Is (Is) 2 (Is) 3 (Is) 4 (Is) 5 (Is) 6 (Is) 10 (Is) 8 (Is) 9 Is Δ=5.8° IGADE Δ=9.5° I26DE Δ=3.0° Flers 2-D effective sound speed profiles Synthetic barograms – CPSM, NRL-G2S

24. Infrasound Technology Workshop – Tokyo, November 2007 24 Δ=5.8° IGADE 45 min Δ=9.5° I26DE 78 min Δ=3.0° Flers 25 min 200 40060080010001200 [km] 2-D effective sound speed profiles Acoustic wave propagation, CPSM

25. Infrasound Technology Workshop – Tokyo, November 2007 25  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 Conclusions I

26. Infrasound Technology Workshop – Tokyo, November 2007 26  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 Conclusions II

27. Infrasound Technology Workshop – Tokyo, November 2007 27  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 Conclusions III

28. Infrasound Technology Workshop – Tokyo, November 2007 28 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 Acknowledgement