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Measurements and Study of the Precursory Infrasonic Waves of Strong Earthquakes from July to September,2000

Su Fang Tian Wei (Department of Basic Sciences,University of Petroleum(Beijing),Beijing 102200,China)  
A new method about measurement of the precursory infrasonic waves of strong earthquake is introduced.A tripartite array in Changping,Beijing was arranged.The infrasonic signals(P-t curve,velocity and direction of wave) stimulated by strong earthquakes from July to Sept,2000 were observed.With fast Fourier transformation,the three-dimensional dynamic frequency spectra were obtained.The results of the spectrum analysis are as follows:(1)10 days or so before occurrence of strong earthquakes,the precursory infrasound of earthquakes with strong amplitude and measurable direction can often be observed.The spectrum characteristics are the amplitudes of precursory infrasound vary from weak(10-20 Pa)to strong(40-80 Pa)or even stronger;their periods are in 2~19 min and 20~65 min respectively at first,and then became 2~65min.Their waveforms are distinctly different from that of meteror shower and strong wind.(2)The maximal amplitude of the precursory infrasound measured is related to not only the magnitude of earthquake,but also the distance and depth of epicenter and other factors.(3)The generating and propagating mechanism of the precursory infrasound of earthquakes are preliminarily explained.(4)If the directions of two remote tripartite arrays intersect,the location of epicenter will be obtained.So the measurements of the precursory infrasound could become a new and more effective method of impending prediction of strong earthquake.
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