The signal to noise ratio disturbance of ionospheric VLF radio signal before the 2010 Yushu M_S7.1 earthquake

In Yushu, Qinghai province, a strong earthquake took place at 23:49:38 UT on April 13, 2010, with a magnitude M_S7.1. Based on ICE experiments onboard the DEMETER satellite, the VLF signal in 10—20 kHz radiated by three ground transmitters and received on board of DEMETER satellite revealed the attenuation of the signal to noise ratio averaged value in the region with a radius of 500 km from the earthquake epicenter in a revisited period of DEMETER just prior to the mainshock. On the other hand, there were no similar phenomena in 2009; on the contrary we found an ascending SNR in the corresponding time interval and spatial position. These ionospheric anomalies before the Yushu earthquake are highly regarded as resulting from the seismo-ionospheric coupling.