VLF radio signal anomalies associated with strong earthquakes

The VLF (Very Low Frequency) radio signal receiving network of Russian Alpha radio navigation system has been established in China since 2010. We applied a quartile-based method to study the variations of VLF signal propagation before the M≥6.0 shallow earthquakes in the network. Results found that possible anomalies occurred around the two strong earthquakes, 2010 M7.1 Yushu and 2013 M7.0 Lushan earthquake, respectively. For earthquakes with magnitude 5.0≥M≥7.0, such anomalies are not detected. Preliminary statistical analysis with Dst and Kp indices show that there exists a good correlation between geomagnetic storms and VLF propagation anomaly.