Regional characteristics of artificial source geoelectric field spatial variations

Knowing the seismic electric signal characteristics will be of great importance for short-term earthquake prediction. In this paper, by studying the signals originated from grounding electrodes 2100--4600 A current of the converter stations in Shaanxi-Gansu-Ningxia-Shanxi region, Sichuan-Yunnan region, Shandong and its surrounding areas as well as Shanghai region in China, we could have a better understanding of regional nature of the geoelectric field variation. The results show that: ① In Shaanxi-Gansu-Ningxia-Shanxi region, the additional geoelectric field originated from Gaoshawo grounding electrode could be observed at ten stations which are distributed along the edge of the Ordos massif arc in the scope of 490 km, but it could not be observed at the stations beyond the distance of 150 km to the west of the source; ② In Sichuan-Yunnan region, the signal strength and the distance between the source and the station that could observe the signals originated from source in southern Lijiang grounding electrode are greater than that in the north. The additional geoelectric field originated from Xichang grounding electrode can be observed only at the stations of Xiaomiao and Xiannüshan which are 10 km and 540 km from the source respectively, and at the other twelve stations the signals could not be observed; ③ The farthest distance and characteristics are different from one another for the signals originated from heavy current observed in the regions of Shandong, Shanghai and Shaanxi-Gansu-Ningxia-Shanxi, as well as Sichuan-Yunnan region; ④ For the studied regions in this paper, the waveform distortion degree of the additional geoelectric field gets higher with the increase of the distance between the source and station. At some stations only the spike pulses were recorded which occurred only when heavy current started and ended. For the characteristics of the additional geoelectric field mentioned above, this paper has made some interpretations from mechanism and geological conditions in order to deepen the understanding of seismic electric signals.