Time Variations in Magnetotelluric Transfer Functions in Kamchatka

   According to the data of long-term monitoring at several sites,
   low-frequency changes of geoelectric field, magnetotelluric impedance and
   magnetic tipper in the period range from first minutes to first hours were
   investigated in the South of Kamchatka. This observation network is
   located on the Pacific shore in the subduction zone.

   According to the long-term monitoring data of the electromagnetic field,
   the intensity of annual geoelectric field variations may reach 100 mV/km,
   while the geomagnetic field intensity may be up to 20-30 nTl. Annual
   variations of both fields are similar. However, the analysis revealed,
   that annual geoelectric field variations cannot be induced by changes in
   geomagnetic field caused by an external ionosphere source. Annual electric
   field variations are of the intra-Earth origin. They may be associated
   with electrochemical, electro-kinetic, filtration and other Earth
   processes. Annual variations are likely to be caused by the changes in the
   activity of these processes due to seasonal intensity of the solar energy,
   affecting the temperature in the near-surface zones of the earth crust.
   Due to this, the geoelectic field intensity varies within a year up to 100
   mV/km. The magnetotelluric impedance behavior (complex environmental
   electric resistance) revealed annual variations. These variations are
   better observed in the impedance modulus at the time period of 500 s,
   where their amplitude is about 30%. At the periods of 1000 and 3000 from
   variation amplitude the impedance moduluses decrease. In impedance phase
   behavior, annual variations are weakly revealed. Their amplitude does not
   exceed the first degrees, i.e. phase measurement accuracy. This shows,
   that impedance annual variations are mainly associated with the change of
   local geoelectric inhomogeneity electric conductivity and of the media in
   the near-surface zones of the earth core.

   Magnetic tipper time changes were investigated for Paratunka observatory.
   Annual variations in the supposed tipper behavior are defined at the
   periods of 1000 - 3000 s. Annual variation in real tipper behavior are not
   defined. The determined peculiarities of magnetic tipper were investigated
   by test geoelectric models of Kamchatka. The results of 3-D numerical
   modeling of a magnetotelluric field show a possible relation of annual
   variations of a supposed tipper at the periods of 1000 - 3000 s with the
   variations in conductivity of deep lateral fault zone. It is suggested,
   that these variations may be caused by the revolution of the Earth around
   the Sun, in the result of which annual cycle appear in geodynamic
   processes expressed in the change of media fracturing, its saturation
   degree by hydrothermal solutions and their mineralization degree.