Infrasound Technology Workshop – Tokyo, November 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
Infrasound Technology Workshop – Tokyo, November 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
Infrasound Technology Workshop – Tokyo, November The Buncefield Explosion 11-Dec :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
Infrasound Technology Workshop – Tokyo, November Recordings of Infrasonic Arrivals
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at Flers: 334 km ▼ microbarometer seismometer duration: 310 seconds, number of phases: 4
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at IGADE: 641 km ▼ duration: 397 seconds, number of phases: 5
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at I26DE: 1057 km duration: 644 seconds, number of phases: 6 ▼ microbarometer seismometer
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at UPPSALA: 1438 km ▼ duration: 454 seconds, number of phases: 5
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at LYCKSELE: 1806 km ▼ NO DETECTION
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at JAMTON: 2033 km ▼ NO DETECTION
Infrasound Technology Workshop – Tokyo, November Infrasound recordings at KIRUNA: 2114 km ▼ NO DETECTION
Infrasound Technology Workshop – Tokyo, November HWM-93 wind model, 11-December :00 (UTC) radial wind 10 kmradial wind 40 km -20 m/s +20 m/s -50 m/s +60 m/s m/s 25°
Infrasound Technology Workshop – Tokyo, November NRL-G2S wind model, 11-December :00 UTC radial wind 10 kmradial wind 40 km m/s 30 m/s -30 m/s -130 m/s +90 m/s ▲ ▲
Infrasound Technology Workshop – Tokyo, November 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 10 km; ~60 40 km Need for 3-D propagation simulations
Infrasound Technology Workshop – Tokyo, November Phase Identification, e.g., Flers ray tracing (1-D τ -p) & WASP-3D phase identification using travel-time curves … and time-frequency analysis
Infrasound Technology Workshop – Tokyo, November Interpretation / Extracting main features – HWM-93 δβ=-0.5° δβ=-1.6° δβ=-2.1° δβ=2.5° δβ=1.2° δβ=1.3°
Infrasound Technology Workshop – Tokyo, November 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°
Infrasound Technology Workshop – Tokyo, November 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: multiple51.05°N0.33°E06:05: NRL-G2S1st51.81°N0.96°W05:59: multiple51.80°N0.24°W06:01:
Infrasound Technology Workshop – Tokyo, November 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: Combined Infrasound Array Data & Coupled Seismic Arrivals β & T DS no model1st51.70°N0.95°W06:02: β & T I & T DS & T SS NRL-G2S1st51.70°N0.35°W06:01: multiple51.67°N0.40°W06:01: 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:
Infrasound Technology Workshop – Tokyo, November 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 …..
Infrasound Technology Workshop – Tokyo, November Single Station Location, I26DE N observations M travel-time curves at Δ origin time:
Infrasound Technology Workshop – Tokyo, November Yield estimate StationFlersIGADEI26DE V D [m/s] A [Pa] max min P WCA [Pa] max min Y [t]max min 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
Infrasound Technology Workshop – Tokyo, November 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
Infrasound Technology Workshop – Tokyo, November Δ=5.8° IGADE 45 min Δ=9.5° I26DE 78 min Δ=3.0° Flers 25 min [km] 2-D effective sound speed profiles Acoustic wave propagation, CPSM
Infrasound Technology Workshop – Tokyo, November 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
Infrasound Technology Workshop – Tokyo, November 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 ( 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
Infrasound Technology Workshop – Tokyo, November 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
Infrasound Technology Workshop – Tokyo, November 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