Analysis of Ionospheric Parameter Dynamics During a Strong Earthquake in Kamchatka on July 29, 2025, Based on a Complex Approach (According to the Data of Ionosphere Vertical Radio Sounding and GNSS)

Using a complex of tools for data recording and analysis, the paper investigates ionospheric parameter dynamics during a strong earthquake in Kamchatka on July 29, 2025 (magnitude M = 8.8). The data of the ionospheric critical frequency foF2 of Paratunka observatory (Kamchatka, IKIR FEB RAS), and the data of the regional GNSS receiver network, located near the earthquake source, were under analysis. Using data from GNSS receivers, the values of absolute vertical total electron content (TEC) and disturbance indices of vertical TEC variations (WTEC) were studied. Data detailed analysis was realized using a new method based on wavelet transform. For the estimates, anomaly intensity measure, characterizing weak, moderate and strong ionospheric disturbances, was used. Before and during the earthquake on July 29, 2025, anomalous changes were distinguished in ionospheric parameter time series. They characterize moderate and intensive oscillation processes in the ionosphere exceeding the background level. A large-scale long (about 2 days) negative anomaly was detected three days and a half before the earthquake against the background of low geomagnetic activity according to the data of Paratunka observatory and GNSS receivers. During the development of the aftershock process, according to data from the Paratunka observatory and data from all GNSS receivers, a large-scale positive anomaly was identified, exceeding in intensity the background variations in ionospheric parameters by three times and more. The positive anomaly lasted for about 2 days. In the region of PAUJ station, the ionospheric disturbances were the most intensive and significantly exceeded in amplitude the disturbances, observed during the period under analysis when geomagnetic activity increased.