Seismo-ionospheric disturbances in VLF signal propagation in connection with two earthquakes in Indonesia in August and September 2018.
Keywords:
low frequency electromagnetic signals, earthquake precursors, lower ionosphereAbstract
We analyse the behaviour of very low frequency (VLF) electromagnetic signal received at the Petropavlovsk-Kamchatsky station in connection with two strong earthquakes which happened in Indonesia. The first earthquake (M = 6.9, h = 10 km) took place in September 19 near the Lombok Island. The second one occurred in September 28 on the Sulawesi Island (М = 7.5, h = 10 km). The analysis revealed the anomalies in dispersion of the night amplitude of the VLF signal which propagated over the seismic area. The anomalies were observed 2-3 days before the both earthquakes. The result of analysis was confirmed by the fact that such effects were absent in signals in other three paths which were far away from the epicentres of the earthquakes. Other possible reasons that may produce disturbances in the ionosphere plasma (space weather, atmospheric circulation) were taken into consideration.