Anomalous phenomena in Schumann resonance band observed in China before the 2011 magnitude 9.0 Tohoku‐Oki earthquake in Japan

Abstract

AbstractThe anomalous phenomena in the Schumann resonance (SR) band, possibly associated with the Tohoku‐Oki earthquake (EQ), are studied based on the ELF observations at two stations in China. The anomaly appeared on 8 March, 3 days prior to the main shock, and was characterized by an increase in the intensity at frequencies from the first mode to the fourth mode in both magnetic field components, different from the observations in Japan before large EQs in Taiwan. The abnormal behaviors of the north‐south and east‐west magnetic field components primarily appeared at 0000–0900 UT and 0200–0900 UT on 8 March, respectively. The finite difference time domain numerical method is applied to model the impact of seismic process on the ELF radio propagation. A partially uniform knee model of the vertical conductivity profile suggested by V. C. Mushtak is used to model the day‐night asymmetric Earth‐ionosphere cavity, and a locally EQ‐induced disturbance model of the atmospheric conductivity is introduced. The atmospheric conductivity is assumed to increase around the epicenter according to the localized enhancement of total electron content in the ionosphere. It is concluded that the SR anomalous phenomena before the Tohoku‐Oki EQ have much to do with the excited sources located at South America and Asia and also with the localized distribution of the disturbed conductivity. This work is a further confirmation of the relationship of SR anomalies with large EQs and has further concluded that the distortions in the SR band before large EQs may be caused by the irregularities located over the shock epicenter in the Earth‐ionosphere cavity by numerical method.