DAM-Île de France épartement Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Infrasound workshop - The Netherlands - October 28-31, 2002 Infrasounds generated by the Infrasounds generated by the China earthquake of Nov. 14, China earthquake of Nov. 14, 2001 (Mm 7.8) 2001 (Mm 7.8) Analysis of ground-coupled air waves Analysis of ground-coupled air waves and distant generation of infrasounds and distant generation of infrasounds detected at I34MN - Mongolia detected at I34MN - Mongolia A. Le Pichon, J. Guilbert, M. Vallée, B. Alcoverro A. Le Pichon, J. Guilbert, M. Vallée, B. Alcoverro J. Virieux, JX Dessa, M. Ulziibat J. Virieux, JX Dessa, M. Ulziibat Mongolian Academy Center Mongolian Academy Center Research Center of Astronomy & Geophysics Research Center of Astronomy & Geophysics Ulaanbaatar-51 Ulaanbaatar-51
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DAM-Île de France
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Infrasounds generated by the China Infrasounds generated by the China earthquake of Nov. 14, 2001 (Mm 7.8)earthquake of Nov. 14, 2001 (Mm 7.8)
Analysis of ground-coupled air waves Analysis of ground-coupled air waves and distant generation of infrasoundsand distant generation of infrasounds
detected at I34MN - Mongoliadetected at I34MN - Mongolia
A. Le Pichon, J. Guilbert, M. Vallée, B. Alcoverro A. Le Pichon, J. Guilbert, M. Vallée, B. Alcoverro J. Virieux, JX Dessa, M. UlziibatJ. Virieux, JX Dessa, M. Ulziibat
Mongolian Academy CenterMongolian Academy CenterResearch Center of Astronomy & GeophysicsResearch Center of Astronomy & GeophysicsUlaanbaatar-51Ulaanbaatar-51
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
11/14/2001 09:26:1090.7°E - 36.0°NMm 7.8D = 1850 km
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Results of PMCC detectionResults of PMCC detection
A B
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
a > 5 10-5 g @ 20 sz > 0.5 cm @ 20 s
0.02 Pa (sens. MB2000 = 10 V/g)
0.05 Pa / P ~ 7.5 Pa c-c
A true seismic / acoustic coupling ? A true seismic / acoustic coupling ? A
MB2000MB2000
LP-ZLP-Z
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Results of PMCC detection - 1DResults of PMCC detection - 1D
B
A
A B
Seismic coupled air waves
Distant generation of infrasound
< 3°v < 10 m/s
B
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
B
A
B
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Infrasound propagation and Infrasound propagation and location of distant source regionslocation of distant source regions
Second approach: Second approach: inverse location procedureinverse location procedure
• Measurements at I34MN: Measurements at I34MN: arrival time and backazimutharrival time and backazimuth• Origin time and epicenter coordinatesOrigin time and epicenter coordinates• Seismic surface waves propagation: Seismic surface waves propagation: VVss ~ 3 km/s @ 20s ~ 3 km/s @ 20s• Acoustic celerity: Acoustic celerity: to be determinedto be determined
First approach: First approach: direct simulationdirect simulation
• Discretization ofDiscretization of fault plane: fault plane: 20 20 x 20 km, 0-60 km depth 20 km, 0-60 km depth• Simulation of the 3C ground displacement: Simulation of the 3C ground displacement: 20 20 x 10°, 10°, [[BouchonBouchon method, 1976] method, 1976]
• Computation of the synthetic pressure field: Computation of the synthetic pressure field: integral equation + ETOPO30integral equation + ETOPO30• Reconstruction of the azimuth time variation at I34MNReconstruction of the azimuth time variation at I34MN• Comparison with measurementsComparison with measurements
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Spatial variations of the HWM-93 wind profilesSpatial variations of the HWM-93 wind profiles
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
3D Ray-tracing results3D Ray-tracing results
It
Isd
2
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
dsRgtrpRgtrpetrpS SnnS
ti )(),()(),(),(2
1,,
Fraunhofer approximation: first order in Fraunhofer approximation: first order in r/rr/rll
Directivity pattern:Directivity pattern:
Cells:Cells: 5 5 x 5 km 5 kmwith T = 20 s,with T = 20 s, kL = 5kL = 5
Integral formulation: Helmholtz-Huygens Integral formulation: Helmholtz-Huygens
)cos()sin(ˆ lllxwith
Simulation of the acoustic propagation Simulation of the acoustic propagation from the topographyfrom the topography
)(
2/ˆ
2/ˆ
1
)sin(
2),( ltti
Lxk
Lxke
rr
ehLtV
ckitrp
N
l ll
ll
l
rrik
lll
l
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Comparison between measurements and simulations at I34MNComparison between measurements and simulations at I34MN
With a 3° azimuth correction, celerity = 0.29 km/sWith a 3° azimuth correction, celerity = 0.29 km/s
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
Qilian ShanQilian Shan
Kunlun ShanKunlun Shan
Tangula ShanTangula Shan
1 2 3
1
2
3
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Infrasound workshop - The Netherlands - October 28-31, 2002Infrasound workshop - The Netherlands - October 28-31, 2002
CONCLUSIONCONCLUSION
• Simulation resultsSimulation results- - The direct and inverse approaches yield the same resultsThe direct and inverse approaches yield the same results- - Good agreements with the measurements using:Good agreements with the measurements using: - line-source hypothesis- line-source hypothesis: : far-field approximation of the integral far-field approximation of the integral equationequation
- velocity model provided by empirical atmospheric profiles- velocity model provided by empirical atmospheric profiles- synthetic seismograms along the fault- synthetic seismograms along the fault
- - Directivity of the radiationDirectivity of the radiation
• Sources of infrasonic wavesSources of infrasonic waves- - Seismic ground-coupled air waves Seismic ground-coupled air waves - - Diffracted pressure waves reradiated by the topography when surface seismic Diffracted pressure waves reradiated by the topography when surface seismic waves carry energy from the rupture pointswaves carry energy from the rupture points- Accurate location of distant source regions: - Accurate location of distant source regions:
- Infrasonic detection generated by large earthquake can be used to validate - Infrasonic detection generated by large earthquake can be used to validate celerity models in the atmospherecelerity models in the atmosphere: : 0.285-0.295 km/s0.285-0.295 km/s
