Вариации характеристик радиоволн ВЧ диапазона над Китаем, сопровождавшие умеренное землетрясение в Японии 5 сентября 2018 г.

Urgency. The Earth's interior layers – atmosphere – ionosphere – magnetosphere (EAIM) form a one system, which is open, dynamic, and nonlinear. There are direct and reverse, positive and negative linkages among the subsystems within the EAIM system, which are currently insufficiently studied. The release of energy from a high-power source in one of the subsystems triggers the interaction among the subsystems. In this paper, a moderate earthquake of Richter magnitude M » 6.6 is considered as such a source. The aim of the paper is to describe time variations in the characteristics of the HF radio waves observed along the radio propagation paths over the People's Republic of China during the earthquake of September 5, 2018 in Japan. Techniques and Methodology. To observe the temporal variations in the characteristics of radio waves, we used the multi-frequency multiple-path coherent radio system at the Harbin Engineering University. Broadcasting stations located in the People's Republic of China, the South Korea, Japan, Russia, and Mongolia are used as transmitters. The time variations in the Doppler spectra, the Doppler shift of frequency of the main mode, and signal amplitudes were subjected to analysis. The measurements were performed in the frequency range of 5 – 10 MHz over 14 radio propagation paths extending from ~ 900 km to 1800 km and having various orientations. The Doppler spectra are calculated in 7.5-s step with the root-mean-square Doppler line error of 0.02 Hz. Results. The response of the ionosphere to a moderate earthquake was observed and studied. The delay time of the assumed response and the apparent speed of propagation of the disturbances were estimated. It was demonstrated that the seismic shock was followed by Doppler spectra spreading and the Doppler frequency shift of the main mode varying with time quasi-periodically with an ~3-min period of infrasound and an ~20 – 30-min period of atmospheric gravity wave. Conclusions: Moderate earthquakes are capable of launching disturbances in the ionosphere detectable at distances of ~1000 km from the epicenter of earthquake.