Correlation characteristics of the geoelectric field with multi-azimuth and multi-pole distance for the same field

At a given site, the correlation coefficient δ_xy between geoelectric field with different azimuths, or δ_xx between geoelectric field with differernt polar distances for the same azimuth can express the complexity of site geoelectric field variation. This paper analyzed the geoelectric field correlation coefficient δ_xy and δ_xx based on the geoelectric field data from more than fifty sites around five typical earthquake epicenters. The results show that δ_xy and δ_xx of a site are relatively stable during a quiet period of seismic activity. During a moderate earthquake, the δ_xy and δ_xx for most of the sites near the epicenter decrease significantly. This phenomenon is directional and quasi-synchronous in time, and gradually disappears with epicentral distance increasing. Furthmore, in viewpoint of mechanism, it is deduced that the decrease in δ_xy and δ_xx reflects the non-uniformity of geoelectric field variation in the local sites near the epicenter.