On the Influence of Meteorological and Hydrological Conditions on Electrotelluric Potentials According to Long-Term Observations at the Khazor-Chashma Station

In 1979–1992, in the central part of the Garm landfill in Tajikistan, an experiment was conducted on continuous (daily) monitoring of electrotelluric potentials (ETPs) on parallel lines with lengths of 2, 10, 40, 150, and 500 m with a common center. The purpose of the measurements was a comprehensive study of processes in the upper part of the Earthʼs crust in a highly seismic area, including an assessment of the influence of exogenous factors (EF) on the measured parameters. However, the results of this experiment have not yet been fully analyzed. In the present work, the reaction of the ETPs to changes in the meteorological and hydrological environment is studied. An approach based on the decomposition of the compared signals into physically determined components with the subsequent use of correlation analysis methods is applied. Special methods have been developed to assess the significance of correlations, taking the special properties of time series of geophysical monitoring into account. The conclusion is made about the surprisingly weak influence of exogenous factors on the measured fields. Such an effect is found only for variations with a characteristic duration from a day to a month, and only for three effects: moisture saturation of the active soil layer, air humidity, and moisture intake into the soil (the total effect of liquid precipitation and snowmelt). The reaction of ETPs to the same changes in EF differs sharply even on lines with a similar length, which is consistent with existing ideas about the mosaic character of ETP variations. The effect of EFs is most pronounced on a 500-m-long line with the largest height difference between the electrodes, more than 20 m.