A possible ULF seismic electro-magnetic emission

Abstract

A possible electro-magnetic emission (EME) associated with earthquakes are presented in the paper through analysis of the anomaly EME in ultra-low frequency range (ULF) observed at some sites before two earthquakes near Beijing and the comparison with similar signals observed prior to the 1988 Armenia and 1989 Loma Prieta earthquakes. The anomaly features are as follows: (1) the anomalous disturbances occur discontinuously several days before earthquakes and signal frequencies are higher remarkably than geomagnetic pulsation and magnetic disturbances during magnetic storms in ULF band and at least not lower than 1 Hz; (2) similar signals are observed by similar observation systems at same site for the same earthquake; (3) the anomaly occurrence times and frequencies at sites near the epicenter are earlier and higher respectively than that at farther sites; (4) the signal energy distribution in different frequency ranges may not be the same and the signal magnitudes may be related to earthquake magnitudes and greater earthquake may emit stronger EME signals; (5) there may be a seismic magnitude threshold for observable ULF EME anomalies and if smaller earthquakes possess of EME signals also, they may not be observed by the present observation system.