Analysis of Pre-Earthquake Space Electric Field Disturbance Observed by CSES

Abstract

In order to explore the abnormal disturbance of the space electric field caused by earthquakes using the electric field data of the ULF and VLF frequency bands of the electric field observed by the ZH-1 satellite, and taking the Mw7.7 earthquake in the Caribbean Sea in the southern sea area of Cuba on 29 January 2020 as an example, the signal-to-noise ratio of the NAA and NLK artificial source VLF transmitting stations in the Northern Hemisphere and the height of the lower ionosphere was calculated. The disturbance of the electric field in the ULF band was extracted using the S-G filtering method. The results indicate that: (1) The ionospheric anomaly caused by this earthquake appeared 20 days before the earthquake, and before the earthquake, there were significant anomalous changes in all parameters within the pregnant seismic zone. The signal-to-noise ratios of the NAA and NLK artificial source transmitter stations decreased by 30%, and the height of the low ionosphere decreased by 5–10 km, while there were anomalous perturbations in several orbits of the ULF electric field, and the magnitude of the perturbations exceeded three times the standard deviation. (2) The SNR of the artificial source transmitting stations before and after the earthquake was significantly reduced in the third period before the earthquake and recovered after the earthquake. (3) The low ionospheric height appears to be reduced before the earthquake and recovers after the earthquake. (4) The decrease in the S/N ratio occurred simultaneously with the decrease in ionospheric height 15 days–10 days before the earthquake. This provides a reference for extracting pre-earthquake ionospheric precursor anomalies.

Keywords

• artificial source VLF transmitter station
• signal to noise ratio
• low ionospheric height
• ULF waveform disturbance