SEISMIC ACTIVITY IN KAMCHATKA AND THE PARAMETERS OF NATURAL ULF/ELF EMISSIONS

Spectral and polarization parameters of the natural ULF/ELF signal in a seismic region (Kamchatka, Russia) are statistically analyzed and a meaningful change in the signal polarization is found to occur several days prior powerful earthquakes (EQ). This effect can be caused by an extended thunderstorm activity in the EQ preparation zone due to either aerosol and gas emissions by an active fault or by the modification of the ionosphere by the preseismic AGW waves. -1 pT/ Hz and conversion function 0.4*F V/(nT*Hz) in the frequency band F=0.003 - 4 Hz and 1.6 V/nT in the band F= 4 - 40 Hz. The sensors for the horizontal components H and D are oriented along the magnetic meridian and transversally to it, and the Z sensor is vertical. Routine data processing includes correction of non-physical data and data gaps, filtration and decimation to the 50 Hz frequency, and calculation of power spectral densities (PSD) of the field components, and the cross- spectra of the horizontal components, with the frequency resolution ~0.2 Hz and time window 30 min. The parameters of the polarization ellipse are calculated following (Born and Wolf, 1964). The orientation angle θ is the angle that the principle axis of polarization ellipse makes with the H axis. The absolute value of the ellipticity (tan(β)) is the ratio of minor to major axis and its sign is determined by the sense of polarization, i.e. β >0 or β<0 as the polarization is right- or left-handed as measured when looking into the propagation wave. Small absolute values of averaged ellipticity do not necessarily correspond to the linear polarization if the dispersion is high. To analyze the degree of signal's linearity a parameter /1 R ab