Electromagnetic phenomena before 2008 Wenchuan M_S8.0 and 2010 Yushu M_S7.1 earthquakes

This paper studied the changes of the geoelectric and geomagnetic fields before the 2008 Wenchuan M_S8.0 earthquake in Sichuan Province and the 2010 Yushu M_S7.1 earthquake in Qinghai Province using the wavelet power spectrum analysis. The results showed that: ① The increased wavelet power value of the geoelectric and geomagnetic fields were observed by the geoelectric stations and the geoelectromagnetic stations near the epicenter before the Wenchuan earthquake. ② The wavelet power value of the geoelectric and geomagentic fields significantly increased in the TIA station and so on in the northeastern margin of Qinghai-Tibet Plateau before the Yushu earthquake， which recovered after the earthquake. ③ The phenomena that the wavelet power value synchronously increased/decreased were recorded more than once at the different channels of different stations near the above two earthquakes. ④ The changes of the wavelet power value were almost same observed by the NS and NW channels of Sandan station and Gufeng station, which are at the same distance from the epicenter of Yushu earthquake. Based on the above analysis， we drew the conclusion preliminarily that the geoelectromagnetic anomalies were mainly caused by the electromagnetic radiation stimulated by the focal development.