We use satellite data to analyze precursory anomalies of the western China Ms 7.1 Yushu earthquake by analyzing the signal-to-noise ratio (SNR) and using the full-wave model to illustrate a possible mechanism for how the anomalies occurred. The results show that very low-frequency (VLF) radio wave SNR in the ionosphere decreased before the Yushu earthquake. The full-wave simulation results confirm that electron density variation in the lower ionosphere will affect VLF radio signal SNR.

This paper addresses the background of electron density (Ne) and temperature (Te and their relationship during local nighttime based on DEMETER satellite data. It also discusses the enhanced negative correlation of Ne and Te around strong earthquakes and the possible electric-field-coupling mechanism as well as digital calculation.