Abstract:
Long-term observations of the telluric potential difference on the measuring lines (L≈100 m) at the Verkhnyaya Paratunka (VP) and Tundrovyi sites on the Kamchatka Peninsula were used to study the tidal response of the electrotelluric field (ETF). This was accomplished by comparing the inferred amplitudes and phases of the harmonic ETF components M2,O1,S1, etc., with the theoretical amplitudes and phases of the respective tidal waves [Melchior, 1968]. Quasi-stationary ETF components with frequencies of the tidal waves O1,M2,K1,P1,S1, and S2, recognizable at both sites, have amplitudes of a few units of μV/m. The VP time–distance curves of the vectors of the M2 and O1 ETF components have an elliptical shape, with their extreme points coinciding in time with phases of 0 and π rad of the tidal waves, implying that the M2 and O1 ETF components are directly related to the respective tides. This relationship is not observed in the ETF components with frequencies of the K1,P1,S1, and S2 waves, indicating that different factors were responsible for their formation,with tidal effects playing an insignificant role. The strain sensitivity of the ETF measuring system at the VP site was estimated; these estimates may prove useful in searching for ETF anomalies premonitory of strong earthquakes. A phenomenological model proposed in our work interprets the behavior of the M2 and O1 ETF components at the VP site in terms of percolation processes in a composite medium containing isotropic and anisotropic layers.