Coseismic Telluric Current Response to the Propagation of Rayleigh Wave from the 2025 Kamchatka Earthquakes (M ≤ 8.8) at Distances of About 6000 km in the Northern Tien Shan Region

A study was performed on the electromagnetic response of the geological medium during the propagation of Rayleigh waves from the 2025 Kamchatka earthquakes (M8.8–7.4) at an epicentral distance of approximately 6000 km. The identities of the coseismic telluric current variations and the propagating Rayleigh wave have been revealed, with their power spectra exhibiting a pronounced quasi-line structure with dominant peaks at 0.04 Hz, 0.054 Hz, and 0.064 Hz. The high correlation of the telluric current response with the Rayleigh wave (r = 0.906, M8.8 and r = 0.83, M7.8) allowed the seismoelectric effect of the second kind to be considered the dominant mechanism for disturbance generation. Electromagnetic signals recorded by the IMS-008 induction sensor showed a lower correlation (r = 0.682), which may be attributed to the shaking of the induction sensor during the passage of the Rayleigh wave, though this does not preclude the presence of a true coseismic signal. Coseismic effects were recorded during the M7.8 and M8.8 earthquakes, but were absent during the M7.4 events. For the first time for the Northern Tien Shan region (at teleseismic distances of approximately 6000 km), key regularities in the generation of the seismoelectric effect during Rayleigh wave propagation have been identified. It is shown that the telluric current response is characterized by a threshold sensitivity to the event magnitude, with the magnitude of induced current variations strictly consistent with the intensity of the seismic wave’s dynamic impact. Utilizing telluric currents as a physical reference for the precise determination of Rayleigh wave arrival times allowed for the refinement of the Rayleigh wave group velocity (3.078–3.093 km/s), reducing calculation uncertainty to 0.5%.