Infrasound Technology Workshop – Tokyo, November 2007 1 The Buncefield Explosion: A benchmark for...

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


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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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


Recordings of Infrasonic Arrivals


Infrasound recordings at Flers: 334 km

▼

microbarometer

seismometer

duration: 310 seconds, number of phases: 4


Infrasound recordings at IGADE: 641 km

▼



Infrasound recordings at I26DE: 1057 km


▼

microbarometer

seismometer


Infrasound recordings at UPPSALA: 1438 km

▼duration: 454 seconds, number of phases: 5


Infrasound recordings at LYCKSELE: 1806 km▼

NO DETECTION


Infrasound recordings at JAMTON: 2033 km ▼

NO DETECTION


Infrasound recordings at KIRUNA: 2114 km ▼

NO DETECTION


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

°


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▲

▲


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


Phase Identification, e.g., Flers

ray tracing(1-D τ-p) & WASP-3D

phase identificationusing

travel-time curves

…and

time-frequency analysis


Interpretation / Extracting main features – HWM-93

δβ=-0.5°

δβ=-1.6°

δβ=-2.1°δβ=2.5°

δβ=1.2°

δβ=1.3°


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°


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


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


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 …..


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


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


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


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


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


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


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


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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