Disturbances of Subionospheric Electromagnetic Signals and Strong Earthquakes (from Observations on the Kamchatka Peninsula in 2023–2024)

Abstract—Observational data from a receiving station in Petropavlovsk-Kamchatskii were used to analyze variations in very low and low frequency (VLF/LF) radio signals associated with two strong (М ≥ 6.5) earthquakes. The Мw 6.5 earthquake of April 3, 2023 occurred in the Avacha Bay, Pacific coast of the Kamchatka Peninsula; the Мw 7.5 earthquake of January 1, 2024 occurred on the Noto Peninsula, Japan. Disturbances in VLF/LW signals were recorded several days before and during the earthquakes on radio paths from two transmitters intersecting the epicentral zones of the earthquakes. Other factors (magnetic storms, cyclones) that could have caused such disturbances were absent at the time of observations. We believe that anomalies in the behavior of radio signals on both paths were caused by the preparatory processes and occurrence of these earthquakes. An additional argument in favor of this interpretation is the absence of anomalies in signal variations on other radio paths remote from the earthquake sources. Wavelet analysis of the amplitude and phase variations of the nighttime signal bandpass filtered in the range of 0.3–15 mHz has shown that the maximum disturbances in the radio signals corresponded to atmospheric internal gravity wave periods of 10–50 min.