Submodal anomalies in Schumann resonance phenomenon possibly associated with earthquakes

Schumann resonance (SR) observations have been carried out at a low latitude station Bichpuri, Agra (Geograph. Lat. 27.2 o N, Long. 78 o E), India using a set of 3-component search coil magnetometer and accessories since 01 April, 2010. Here, we analyse the data for a period of one year from 01 January to 31 December, 2013 in search of possible anomalies in SR data associated with earthquakes. We find that unusual submodal amplitude enhancements ≈ 10-15 dB, frequency shifts 1 Hz-4Hz, precursory period 7 days and duration of the anomaly ≈ 6 hours occurred beyond third and fourth SR bands associated with 03 major earthquakes (M > 6.0). The earthquakes occurred in neighbouring countries of China and Pakistan around India in the months of July and September, 2013. We show that the anomalies appeared as a result of constructive interference maxima at the receiver between the direct ELF waves generated from African and South Asian thunderstorm centers and reflected from the disturbances over epicentres of earthquakes.