Ionospheric precursors of earthquakes in July 2025 in Kamchatka region

Earthquakes of the second half of July reminded again that we live in the seismically active region. At the same time, scientists do not stop investigation of physical processes, which accompany earthquake preparation at different phases, and development of methods and forecast tools based on them.

As multiple researches show, ionospheric effects associated with earthquakes appear both before and after earth shocks. Seismo-ionospehric anomaly occurrences may be the sequences of penetration of electric field and/or acoustic-gravity waves into the ionosphere. They are excited in the near ground atmosphere over the earthquake preparation zone.

Seismo-ionospheric effects have been under investigation at IKIR FEB RAS for many years. Nevertheless, it is difficult to interpret ionospheric data in each case unambiguously as long as ionosphere is very changeable and exposed to the action of different helio-geophysical factors.

Thus, possible ionospheric precursors of earthquakes are identified by a certain set of morphological features. The results, obtained by long-term observations at the ground stations of vertical ionospheric sounding, show that the processes of strong earthquake preparation may affect frequency and height parameters, characterizing the states of the lower (E region) and upper (F region) ionosphere.

Based on ionospheric observations, carried out at IKIR FEB RAS from July 10 to 16, 2025, the researcher of the Laboratory of System Analysis of Atmospheric Processes, Cand. Sci. (Phys.-Math.) Pavlov Alexey, detected formation of the following ionospheric anomalies:

• precipitation of charged particles from radiation belts into the ionosphere (formation of K-layer) on July 12-14, 2025;
• formation of sporadic Es layer of r type on July 11-13 2025;
• formation of diffusive sporadic Es layer (Es-spread) on July 10-12 and 14, 2025;
• screening of F2 layer on July 10, 14 and 16, 2025;
• exceedance of relative deviations of foF2 critical frequency values from median values by 20 % during geomagnetic disturbances on July 11, 2025;
• split trace on the ionograms near the foF2 critical frequency on July 11, 13 and 15, 2025.

According to the A.A. Gusev method, based on ionospheric anomaly data complex for earthquakes with M≥5.0, the forecast efficiency was JG=1.35. The forecast veracity was V=0.46 and the reliability was R=0.45.

The estimated probability of earthquake occurrence with M≥5.0 in the geographical region with the coordinates 48°‒58° N and 154°‒167° E for the waiting period of July 14-21, 2025 was P=0.51.

Exceedance of the ionospheric parameters h'Es, foEs, fbEs and hmF2 for the upper boundaries of their background values during moderate geomagnetic activity conditions was also detected during the period of July 18-19, 2025. According to the A.A. Gusev method, the forecast efficiency was JG= 1.8 based on ionospheric anomaly data complex for earthquakes with M≥5.0. The forecast veracity was V= 0.36 and the reliability was R=0.51 .

The estimated probability of earthquake occurrence with M≥5.0 in the geographical region with the coordinates 48°‒58° N and 154°‒167° E for the waiting period of July 19-26, 2025 was P=0.6.

Thus, the earthquakes corresponded to the forecasts and the estimates for seismic state development based on ionospheric observations.

The figure shows time series of the ionospheric parameters h'Es, foEs, fbEs, foF2, hmF2 and the geomagnetic index K on July 10-20, 2025. Dashed lines show median values and boundaries of background value ranges for the ionospheric parameters, respectively. The identified anomalies are indicated with red 'x'. Earthquakes with M≥6.0 are indicated on the time axis with red triangles.