1. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Infrasounds generated by the China earthquake of Nov. 14, 2001 (Mm 7.8) Analysis of ground-coupled air waves and distant generation of infrasounds detected at I34MN - Mongolia A. Le Pichon, J. Guilbert, M. Vallée, B. Alcoverro J. Virieux, JX Dessa, M. Ulziibat Mongolian Academy Center Research Center of Astronomy & Geophysics Ulaanbaatar-51

2. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 11/14/2001 09:26:10 90.7°E - 36.0°N Mm 7.8 D = 1850 km

3. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Results of PMCC detection AB

4. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 a > 5 10 -5 g @ 20 s  z > 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 MB2000 LP-Z

5. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Results of PMCC detection - 1D B A AB Seismic coupled air waves Distant generation of infrasound  < 3°  v < 10 m/s B

6. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 B A B

7. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Infrasound propagation and location of distant source regions Second approach: inverse location procedure Measurements at I34MN: arrival time and backazimuth Measurements at I34MN: arrival time and backazimuth Origin time and epicenter coordinates Origin time and epicenter coordinates Seismic surface waves propagation: V s ~ 3 km/s @ 20s Seismic surface waves propagation: V s ~ 3 km/s @ 20s Acoustic celerity: to be determined Acoustic celerity: to be determined First approach: direct simulation Discretization of fault plane: 20 20 km, 0-60 km depth Discretization of fault plane: 20 x 20 km, 0-60 km depth Simulation of the 3C ground displacement: 20 10°, [Bouchon method, 1976] Simulation of the 3C ground displacement: 20 x 10°, [Bouchon method, 1976] Computation of the synthetic pressure field: integral equation + ETOPO30 Computation of the synthetic pressure field: integral equation + ETOPO30 Reconstruction of the azimuth time variation at I34MN Reconstruction of the azimuth time variation at I34MN Comparison with measurements Comparison with measurements

8. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Spatial variations of the HWM-93 wind profiles

9. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 3D Ray-tracing results It Isd 2

10. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Fraunhofer approximation: first order in r/r l Directivity pattern: Cells: 5 5 km Cells: 5 x 5 km with T = 20 s, kL = 5 Integral formulation: Helmholtz-Huygens Simulation of the acoustic propagation from the topography

11. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Comparison between measurements and simulations at I34MN With a 3° azimuth correction, celerity = 0.29 km/s

12. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 Qilian Shan Kunlun Shan Tangula Shan 123 1 2 3

13. DAM-Île de France Département Analyse, Surveillance, Environnement Infrasound workshop - The Netherlands - October 28-31, 2002 CONCLUSION Simulation results Simulation results - The direct and inverse approaches yield the same results - Good agreements with the measurements using: - line-source hypothesis : far-field approximation of the integral equation - line-source hypothesis : far-field approximation of the integral equation - velocity model provided by empirical atmospheric profiles - synthetic seismograms along the fault - Directivity of the radiation Sources of infrasonic waves Sources of infrasonic waves - Seismic ground-coupled air waves - Diffracted pressure waves reradiated by the topography when surface seismic waves carry energy from the rupture points - Accurate location of distant source regions: - propagation range: 1500-2000 km - horizontal scale size: 10 10 ° - horizontal scale size: 10 x 10 ° - Infrasonic detection generated by large earthquake can be used to validate celerity models in the atmosphere : 0.285-0.295 km/s