Effects of the India–Pakistan border earthquake on the atmospherics at 6 kHz and 9 kHz recorded at Tripura

The unusual variations observed in the records of the integrated field intensity of the atmospherics (IFIA) at 6 kHz and 9 kHz at Agartala, Tripura, in the north-eastern state of India (latitude, 23 ˚ N; longitude, 91.4 ˚ E) during the large earthquake on October 8, 2005 at Muzaffarabad (latitude, 34.53 ˚ N; longitude, 73.58 ˚ E) in Kashmir in Pakistan are here analyzed. Spiky variations in the IFIA at 6 kHz and 9 kHz were observed several days previous to the day of the earthquake (from midnight, September 28, 2005). The effects persisted for some days, decayed gradually, and eventually ceased on October 31, 2005. The spikes are distinctly superimposed on the ambient level, with mutual separation of 2–5 mins. The number of spikes per day and the total duration of their occurrence were particularly high on the day of the earthquake. The spike heights are higher at 6 kHz than at 9 kHz. The results are discussed here. The generation of electromagnetic radiation associated with the fracture of rocks, the subsequent penetration of this radiation into the Earth atmosphere, and finally its propagation through the Earth–ionosphere waveguide may be responsible for these observed spikes. The present observations show that the very low frequency anomaly dominates between 6 kHz and 9 kHz. The nature of the spikes presented here is a characteristic feature of the IFIA during the period of the earthquake. This has been established on the basis of time-series analyses over a period of one year. 1