Research of Abnormal Infrasound Signals before Worldwide Earthquakes

According to the U.S.Geological Survey,there are 92 earthquakes that M≥7.0 happened worldwide from 2002 to 2008.About 78 of these earthquakes or 84.8% are preceded the signals.The amplitudes of these abnormal infrasound signals were greater than 1000mV,and the frequency of the abnormal infrasound signals was about 10-3Hz.There are 45 or 57.7% of these earthquakes happened within 9 days after the abnormal signals were recorded.In this paper,92 worldwide earthquakes were investigated,and the relationship between the earthquake magnitude,M,the distance of observation points to the epicenter,D and the maximum amplitude of the abnormal signal,U_m.The results show that the infrasound abnormal signals have good correlation with earthquakes,but U_m vs.M,and D are the complicated relationship.