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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
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
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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 ofLondon
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 allover central Europe
Infrasound Technology Workshop – Tokyo, November 2007 4
Recordings of Infrasonic Arrivals
Infrasound Technology Workshop – Tokyo, November 2007 5
Infrasound recordings at Flers: 334 km
▼
microbarometer
seismometer
duration: 310 seconds, number of phases: 4
Infrasound Technology Workshop – Tokyo, November 2007 6
Infrasound recordings at IGADE: 641 km
▼
duration: 397 seconds, number of phases: 5
Infrasound Technology Workshop – Tokyo, November 2007 7
Infrasound recordings at I26DE: 1057 km
duration: 644 seconds, number of phases: 6
▼
microbarometer
seismometer
Infrasound Technology Workshop – Tokyo, November 2007 8
Infrasound recordings at UPPSALA: 1438 km
▼duration: 454 seconds, number of phases: 5
Infrasound Technology Workshop – Tokyo, November 2007 9
Infrasound recordings at LYCKSELE: 1806 km▼
NO DETECTION
Infrasound Technology Workshop – Tokyo, November 2007 10
Infrasound recordings at JAMTON: 2033 km ▼
NO DETECTION
Infrasound Technology Workshop – Tokyo, November 2007 11
Infrasound recordings at KIRUNA: 2114 km ▼
NO DETECTION
Infrasound Technology Workshop – Tokyo, November 2007 12
HWM-93 wind model, 11-December-2005 06:00 (UTC)
radial wind speed @ 10 km radial wind speed @ 40 km
-20 m/s
+20 m/s-50 m/s-50 m/s
+60 m/s
m/s m/s25
°
Infrasound Technology Workshop – Tokyo, November 2007 13
NRL-G2S wind model, 11-December-2005 06:00 UTC
radial wind speed @ 10 km radial wind speed @ 40 kmm/s m/s
30 m/s
-30 m/s -130 m/s
+90 m/s▲
▲
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
Infrasound Technology Workshop – Tokyo, November 2007 15
Phase Identification, e.g., Flers
ray tracing(1-D τ-p) & WASP-3D
phase identificationusing
travel-time curves
…and
time-frequency analysis
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°
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°
Infrasound Technology Workshop – Tokyo, November 2007 18
Location Results (I)
Location Configuration Latitude Longitude Origin time11/12/05
Δd [km]
Δt [s]
ground truth 51.78° N 0.43° W 06:01:31
Infrasound Array Data Only
β no model 1st 51.24°N 1.72°E - 161 -
multiple 51.00°N 1.54°E - 162 -
HWM-93 1st 51.61°N 1.75°E - 152 -
multiple 51.40°N 1.64°E - 149 -
NRL-G2S 1st 51.65°N 0.94°E - 96 -
multiple 51.89°N 0.96°W - 38 -
β & TI HWM-93 1st 51.15°N 0.71°E 06:07:41 114 370
multiple 51.05°N 0.33°E 06:05:33 88 242
NRL-G2S 1st 51.81°N 0.96°W 05:59:30 37 -121
multiple 51.80°N 0.24°W 06:01:18 13 -13
Infrasound Technology Workshop – Tokyo, November 2007 19
Location Results (II)
Location Configuration Latitude Longitude Origin time11/12/05
Δd [km]
Δt [s]
ground truth 51.78° N 0.43° W 06:01:31
Coupled Seismic Arrivals Only
TDS no model 1st 51.74°N 0.41°W 06:01:28 5 -3
TDS & TSS no model 1st 51.68°N 0.41°W 06:01: 32 11 1
Combined Infrasound Array Data & Coupled Seismic Arrivals
β & TDS no model 1st 51.70°N 0.95°W 06:02:38 37 67
β & TI &
TDS & TSS
NRL-G2S 1st 51.70°N 0.35°W 06:01:24 10 -7
multiple 51.67°N 0.40°W 06:01:30 12 -2
Single Infrasound Array Data: Flers
β & TI NRL-G2S multiple 51.72°N 0.58°W 06:01:33 12 2
Single Infrasound Array Data: I26DE
β & TI NRL-G2S multiple 51.97°N 0.68°W 06:00:19 28 -72
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 Trms → [Δ, torig, δβ]• next iteration …..
Infrasound Technology Workshop – Tokyo, November 2007 21
Single Station Location, I26DE
N
j
M
k
obsj
calck
origrms ttt
NT
1
2
1
min1 • N observations
• M travel-time curves at Δ• origin time: ctt obsorig /
1
Infrasound Technology Workshop – Tokyo, November 2007 22
Yield estimate
Station Flers IGADE I26DE
VD [m/s] 15 91 95
A [Pa]
max 1.35 5.95 4.88
min 0.45 3.87 1.67
PWCA
[Pa]
max 0.73 0.14 0.10
min 0.24 0.09 0.03
Y [t] max 153 53 85
min 32 29 19
median - - 33
chgwtSR
PP
SRPdV
rawwca
wca
2
10
)(1095.5018.0
4072.14
[Whitaker et al., 2003; Evers et al. 2007]
yield varies between 19 and 153 t HE300 t vapor cloud → ~30 t HE
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
Iw
Is
(Is)2
(Is)2 (Is)3 (Is)4 (Is)5 (Is)6 (Is)10(Is)8 (Is)9Is
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 2007 24
Δ=5.8°IGADE45 min
Δ=9.5°I26DE78 min
Δ=3.0°Flers25 min
200 400 600 800 1000 1200 [km]
2-D effective sound speed profiles
Acoustic wave propagation, CPSM
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
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
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
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
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