Abstract: We studied changes of geoelectric fields before and after the 2013 Lushan M_S7.0 earthquake in Sichuan Province and Minxiang—Zhangxian M_S6.6 earthquake in Gansu Province observed by the Pingliang and other stations around the epicenter. The results show that: ① Before Lushan M_S7.0 earthquake and Minxiang—Zhangxian M_S6.6 earthquake, significant anomalies of geoelectric fields were recorded by Pingliang station. ② Maximum entropy method was used to calculate geoelectric data observed by Pingliang, Songshan and Gufeng stations before and after the Lushan earthquake and Minxian—zhangxian earthquake, and the calculation reaults reveal that the phenomenon of increased power spectrum density (especially, anomalies of low frequency components under 4×10³ Hz) occurred before the earthquake, and the phenomenon observed by some stations disappeared after the Minxian—Zhangxian earthquake. ③ The nearer the location is to the epicenter, the more obvious change the power spectrum density anomalies and the weaker the correlation between long polar distance and short polar distance becomes. In the primary analysis for this phenomenon, we propose that the deformation of underground medium under stations in the process of earthquake preparation may stimulate macroscopic electromagnetic radiation.

Key words: Geo-electric field, Lushan M_S7.0 Earthquake, Minxian—zhangxian M_S6.6 Earthquake