Abstract: Amplitude data from six propagation paths formed by three Alpha transmitters in Russia and two Alpha navigation signal monitors in Ya’an and Tonghai have been used to study the 2010 Yushu M7.3 earthquake. It has been found that the f1 amplitude on the paths of Novosibirsk-Ya’an and Novosibirsk-Tonghai has appeared prominently negative anomalies at about Beijing time 10:30, 3 days before Yushu earthquake which has lasting for about 15 minutes. High correlation of two anomalies on the two different paths may be caused by the same ionospheric disturbance. Comparing the data on April 14 with the background data, it has been found that the f1 amplitude on the paths of Krasnodar and Khabarovsk stations with Ya’an and Tonghai have no disturbances, which further suggested that this perturbation of the lower ionosphere is located in the valid detection range of Novosibirsk-Ya'an and Novosibirsk-Tonghai paths. In addition, there has been no significant anomaly at f2 and f3, which means the perturbation of the lower ionosphere is outside the detection range of f2 and f3 frequency. Comprehensive analysis on these results could provide scientific basis for locating the disturbance of the lower ionosphere. The method adopted in this article can be used effectively in extracting seismic anomalies from Alpha monitor data in the future.

Key words: Seismic anomaly, VLF radio wave, Alpha signal, The 2010 Yushu Earthquake