Study on the Geo‐Electric Field Variation of Sichuan Lushan M_S7.0 and Wenchuan M_S8.0 Earthquake

Abstract

Applying the data of geo-electric field observation stations surrounding the epicenter of Sichuan Lushan Ms7.0 and Wenchuan Ms8.0 earthquake, mainly using electric field waveform comparison and polarization orientation changes of two kinds of methods, and combining the observation log of stations, we study and analyze the data of the geo-electric field station before the two earthquakes and conclude that, the anomalous waveform variation before the Lushan Ms7.0 and Wenchuan Ms8.0 earthquake showed mainly two forms: diurnal waveform distortion (such as Yanyuan station and Lugu Hu station) and the change of geo-electric field frequency spectrum characteristics in the corresponding time, and these variations basically appeared in 1∼2 months before the earthquake. Using the daily mean value of geo-electric field observed by part of stations around the epicenter of two earthquakes, we calculated the polarization of geo-electric field before two earthquakes, and found a sharp change in the polarization direction before the earthquake, the largest change was 160• , and the minimum change was 10• . A preliminary study also found that, before the two earthquakes, the intersection region of the forward or reverse extension line of polarization orientation and the epicenter seem to have some sort of connection. For the results obtained in this study, a tentative theoretical explanation was given based on the generation mechanism of seismic electric signals and the focal mechanism of the two earthquakes.