october 2003 1 the woomera infrasound and seismic experiment david brown 1 ; clive collins 1 ; brian...

October 2003

1

The Woomera Infrasound and

Seismic Experiment

David Brown1; Clive Collins1; Brian Kennett2

1. Geoscience Australia2. Australian National University

Geological Survey of CanadaAustralian Dept. of Defence

October 2003

2

Introduction

The Woomera Experimento An international explosives trial held at Woomera, South Australia, in September, October 2002

o Conducted for defence research by:• UK Ministry of Defence• Australian Department of Defence

o Purpose:o ammunition stewardship program

o Participation by:• Canada• Netherlands• Norway• USA• Singapore

o Two explosions:• 27000 kg ammunition• 5000 kg ammunition

o Portable network of sensors was deployed:• 2 three-sensor infrasound arrays• 18 seismometers

IS07

October 2003

3

Woomera

Broken Hill

Introduction

167m

315m

1165m

900 m

Flinders Ranges

October 2003

4

Explosion Date (UT) Time (UT) Charge Size(kg)

Latitude(deg)

Longitude(deg)

1 20/09/2002 00:38:02.79 ± 0.06 27,050 -31.0108 136.7756

2 07/10/2002 01:08:04.39 ± 0.03 5,000 -31.0134 136.7857

Source Information

The Source

October 2003

The Source

Earthen walls 3 sidesConcrete roof

Explosives ContainerInstruments, tamping

October 2003

The Source

Some statistics

for a block of rubble

T = 33.57 sec = 508 m

V = 165.2 m/sH = 1380.5 m= 84.7 deg

27000 kg shot

Shock waveShock wave

October 2003

7

The Source

Norwegian house Australian house

October 2003

8

Station Distance(km)

Backazimuth(deg)

Sensor

IS07 1257 167.7 8 x MB2000

BH 467 283.0 3 x MB2000

OOD 476 161.1 3 x MB2000

Infrasound Receiver Information

StationDistance

(km)Backazimuth

(deg) Sensor

W660W 0.7 99.1 L4C HSA3

W660S 0.7 355.1 L4C HSA3

W04K 4.0 289.4 Guralp CMGT240




24KM 24.1 346.9 Guralp CMGT240






W100K 100.5 330.4 Guralp CMGT240

W125K 124.9 330.1 Guralp CMGT240

W150K 151.7 333.0 Guralp CMGT240

W175K 175.2 331.8 Guralp CMGT240

W200K 196.8 329.8 Guralp CMGT240

W250K 251.5 319.5 Guralp CMGT240

Seismic Receiver Information

Receiver Information

October 2003

Spectrogram: 20,000 lb Chemical Explosion @ 250 km 180 deg. backazimuth

• Broad-band signal• signal duration: 0.6 min• dominant period 1.6 sec• drop-off frequency:

– 6db down: > 2.0 Hz– 12 db down > 2.0 Hz

• Fstat– @ max SNR: 4.3– @Max Power: 21.5

• Frequency:– @max SNR 2.0 Hz– @max Power 0.47 Hz

• Need to design a 3-sensor array with maximum capability around 0.5 Hz. ie, average intersensor spacing of around 330 m.


October 2003

10


Broken Hill Station Finite-frequency array response

October 2003

11

Broken Hill Station


October 2003

12


Oodnadatta StationFinite-frequency array response

October 2003

13

Oodnadatta Station


October 2003

14


IS07 StationFinite-frequency array response

October 2003

15


October 2003

16

The Signals

Broken Hill Station 27000 kg

October 2003

17

line Horizontal

velocity

m/s

H 340

A 310

B 300

C 290

D 280

E 270

F 260

G 250

The Signals


0.8 – 3.2 Hz

October 2003

18

342 m/s289 deg

354 m/s290 deg

348 m/s290 deg

454 m/s256 deg 477 m/s

257 deg490 m/s241 deg

The Signals


October 2003

19

line Horizontal

velocity

m/s

A 320

B 310

C 300

The Signals

IS07 27000 kg 352 m/s167 deg

October 2003

20

The Signals

Oodnadatta Station 27000 kg

line Horizontal

velocity

m/s

A 340

B 330

C 320

0.8 – 3.2 Hz

October 2003

21

The Signals


line Horizontal

velocity

m/s

A 350

B 340

C 330

0.4 – 1.6 Hz

October 2003

22

GA Infrasonic Processing for CTBT monitoring

Infrasonic Processing at Geoscience Australiao Will process 5 IMS stations: IS03, IS04, IS05, IS06, IS07o Will observe the following processing philosophy

Single station processing: Seeking significant signals on individual stations

INFERAutomatic detector

detection

Interactive Analysisscanning

DISCINSimple discrimination criteria

arrival

Interactive Analysisreview

arrival

Automatic internal alert notification

rawdata

DISCEXHigh-level discrimination procedures

Manual external alert notification

duration > 2 minutesFstat > 10.0SNR > 1.5

Knowledge of local sources

SH investigation

Radionuclide investigation

Source Characterization study

57 days38185 detects 98 arrivals

1 arrival

October 2003

Signal parameter estimation at sparse arrays• Global minimisation of the misfit between theoretical and stacked beam powers• theoretical side-lobe pattern will be imprinted on the stacked beam power

ωω

ω

ωdeS

j

i j∫ ∑Δ⋅

=2

1

2

),(sr

sp

p

i

piip BSM

/181

1

)(),(81

1)( ⎟⎟

⎠

⎞⎜⎜⎝

⎛−= ∑

=sspp

ωωω

ω

ωdexB

j

ij

j∫ ∑⋅

=2

1

2

)(ˆ)(pr

p

Define broad-band theoretical array response to be

Define broad-band stacked beam-power to be

Define the misfit function using an norm as pL

Use the Sambridge Neighbourhood Algorithm to converge to the region of best fit.


October 2003

Array response• Beam power as a function of slowness for I07AU array • Zero slowness • finite frequency signal centred at 0.875 Hz• 9 x 9 = 81 beams were used• maximum beam power centred on zero slowness

3

3

-3

-3

Sx (s/km)

Sy(s/km)

Signal Reception and Detection: Sparse Arrays


October 2003

0 720 1440 2160 2880 3600

Time (sec)

Synthetic implant, azimuth, 128 deg. 3

-3

-3

3

Sx (s/km)

Sy

N

S

EWArray response• Beam power as a function of slowness for I07AU array with implanted signal• 9 x 9 = 81 beams were used• 0.875 Hz• maximum beam power centred on slowness corresponding to the implant azimuth (128 deg)

Slowness plane



October 2003

misfit surface3.1L



October 2003

equals

minus

Signal Reception and Detection: Sparse ArraysN

S

EW

N

S

W E

N

S

EW


81 beams: 1.5 deg accuracy in azimuth

[BSSA, 2003, Vol 93 p.1765-1772]

October 2003

28

• Determine the Great-circle intersection point

• Determine the travel-times to receivers using a two-value constant velocity model :

290 m/s (stratospheric propagation)240 m/s (thermospheric propagation)

• Determine if predicted travel-times match observed arrival times for both stations (up to some variance)

• Use uncertainty in measured azimuth to determine uncertainty in predicted source location


detectionINFRA_LOC_0

automatic 2 station source location

origin

INFRA_LOC_1automatic

source location(refinement level 1)

INFRA_LOC_2automatic

source location(refinement level 2)

Network processing: Infrasonic source location

> 2 stations

Updated travel-timeInformation. GT information for testingData Fusion

origin

origin

October 2003

29

Summary

The Woomera Infrasound and Seismic experimento Characterised by unusually fast travel-times

• May be timing errors (unlikely)o Characterised by significant off-great circle azimuths

• may be side-lobe detections (unlikely)o May be acoustic signal generated by the seismic interaction with the Flinders

Ranges (?)

GA Infrasonic Processingo Seeks significant signals on individual stations first

• Basic set of discrimination criteria for automatic alert notification− Duration, Coherence, Energy

o Performs 2-station source location using constant velocity modelo Will experiment with the Kennett procedure for sparse array processing

• May help the spatial aliasing problem at sparse arrays

october 2003 1 the woomera infrasound and seismic experiment david brown 1 ; clive collins 1 ; brian...

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