Kamchatka Megaearthquake on July 29, 2025: Reflection of the Preparation Process in the Results of Multi-Instrumental Geophysical Measurements in the Avacha Bay Area

This article discusses the results of long-term multi-instrumental geophysical measurements in the Avacha Bay area (the eastern coast of Kamchatka), conducted for the purpose of medium- and short-term seismic hazard prediction for the Petropavlovsk-Kamchatsky region. The most important results, reflecting the starting process of the Kamchatka megaearthquake (July 29, 2025, MW = 8.8), were obtained using data from the Multi-Instrumental Borehole Measurement Network, as well as data from monitoring changes in the total electron content of the ionosphere. Data obtained from six types of borehole measurements are used to monitor the initial processes of large earthquakes in the Avacha Bay area. The basic types of monitoring are two original methods developed by the authors: a method for monitoring changes in the specific electrical resistance (SER) of the geoenvironment using underground electrical antennas, and a method for monitoring changes in the geoenvironment moisture based on borehole geoacoustic measurement data. It is shown that a record-breaking SER anomaly (amplitude, duration) formed in the Avacha Bay area on the eve of the Kamchatka megaearthquake. This anomaly was reflected in SER monitoring data for a monitoring depth of 2200 m beginning in mid-2018, and in data for a depth of 950 m in early 2021. Since January 2014, the Laboratory for Multi-Instrumental Monitoring of Seismically Active Environments at the Institute of Volcanology and Seismology of the Far Eastern Branch of the Russian Academy of Sciences (IVS FEB RAS) has been regularly (usually every two weeks) preparing conclusions with seismic hazard assessments for the Petropavlovsk-Kamchatsky agglomeration area based on the current results of geophysical measurements in the Avacha Bay area. The research focused not on accurately predicting the timing and parameters of a strong earthquake (which is inherently impossible) but on probabilistically assessing the current seismic hazard for the Petropavlovsk-Kamchatsky agglomeration. This approach enabled the authors to successfully predict two strong foreshocks of the Kamchatka megaearthquake – the Shipunskoye-1 earthquake (August 17, 2024; MW = 7.0) and the Shipunskoye-2 earthquake (July 20, 2025, MW = 7.4), which caused tremors of up to points 6.0 in Petropavlovsk-Kamchatsky.