Pre-earthquake Electric Field Disturbances and Interference Analysis Based on CSES-01 Satellite Observations

Abstract

Anomalous electromagnetic phenomena in the ionosphere before seismic activity have been identified as potential indicators for earthquake early warning. Data from the CSES-01 satellite were analyzed using the STL decomposition method to break down electric field time series into longitudinal, latitudinal, and residual components. To quantify disturbance intensity, we use theC-value, a spectrum-fitting index derived from the power-law relationship between electric-field power spectral density and frequency. The longitudinal and latitudinal components reveal the electric field's double periodicity, characterized by a V-shape from south to north and a bimodal shape from east to west. After isolating conventional periodic disturbances with a strength of 0.87, unconventional disturbances in the residual component were examined to identify seismic precursor anomalies. Electric field power density disturbances associated with the 11 May 2023, Tonga Islands magnitude 7.6 earthquake were extracted. Multiple significant anomalies in the ionospheric electric field were detected within 20d prior to the earthquake: an initial anomaly with aC-value exceeding 3.5 appeared 20d before; a persistent anomaly with a peakC-value of 3.9 occurred 13 to 11d prior; a sharp increase to a peakC-value of 4.4, three times the standard deviation, was observed 7d prior; disturbances decreased until a resurgence 4d prior, with a peakC-value of 3.5 lasting 2d; theC-value returned to baseline 1d before the earthquake. The STL-C method effectively differentiates various causal disturbances in the ionospheric electric field, offering novel approaches and insights for studying seismic precursors.