Abnormal infrasound signals before 92 M ≧ 7.0 worldwide earthquakes during 2002-2008

In this paper, 240 abnormal infrasound signals observed at Beijing (39.87°N, 116.48°E) and 92 M ≧ 7.0 worldwide earthquakes during 2002-2008 are investigated. It is found that about 85% the earthquakes are preceded the signals by 1-30 days and the greater M ≧ 7.6 earthquakes are most likely leaded by 1-10 days. The maximum amplitude of the abnormal infrasound signal generally exceeds 8 Pa in sound pressure. The statistical analyses further indicate that the amplitude of the abnormal signals is proportional to the magnitude the associated forthcoming earthquake but inversely to the distance from that earthquake to the observation station.