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.

The CSES observed ionospheric Pc1 waves near the wave injection regions in conjugate hemispheres during the recovery phase of the geomagnetic storm on 27 August 2018. The Pc1s were found to be Alfvén waves with mixed polarisation propagating along background magnetic lines in the ionosphere. We suggest that the possible sources of Pc1 are EMIC waves generated near the plasmapause by the outward expansion of the plasmasphere into the ring current during the recovery phase of geomagnetic storms.