Study On The Characteristics Of Electric Field Disturbance Before Strong Earthquakes Based On CSES Observation

On February 2,2018,China’s first earthquake electromagnetic monitoring test satellite,the China Seismo-Electromagnetic Satellite(CSES),was launched into orbit.It has been operating for more than 5 years,conducting real-time monitoring of the ionosphere dynamics and earthquake precursor tracking in China and surrounding areas.It has accumulated various space parameter data,such as the intensity of the space electromagnetic field,ionospheric plasma temperature,and high-energy particle density,before and after earthquakes of magnitude 7 or higher globally and magnitude6 or higher in China.Domestic and foreign researchers have used data from the CSES to conduct theoretical and experimental research on space ionospheric observation and electromagnetic monitoring,identifying abnormal disturbances in the ionosphere before and after earthquakes and exploring the mechanism of earthquake ionospheric disturbances,providing rich theoretical and methodological support for earthquake monitoring work.This paper uses the C-value method to preliminarily process the power spectral data of the ionospheric electric field ELF(19.5～250Hz)observed by the electric field detector on the CSES.By constructing a stable background field observation model,the disturbance amplitude of the electric field above the epicenter relative to the background field is extracted.The spatial and temporal evolution characteristics of the spatial electric field before and after earthquakes with different attributes are statistically analyzed using the superposition analysis method.The consistency and differences between the results of the earthquake examples and the electric field model of the earthquake ionosphere are discussed and analyzed.The results are as follows:(1)Based on the ELF data observed by the CSES,the C-value method can also identify the anomalous changes in the power spectrum data in the ELF frequency band(19.5Hz～250Hz),and the changes are manifested in the concentration of the anomalous values in one range,and the great values of C-values before and after the earthquake first rise and then fall with time,and the very small values first fall and then return to the normal level.It proves that the data quality observed by CSES is reliable.(2)Through the analysis of the C-value method,the θ-value method is proposed.Then,the C-value method and the θ-value method are used to analyze the ELF data of the ionospheric electric field observed by the CSES before and after earthquakes of two different seismic source types.The observation of the θ-value shows that the earthquake in the southern waters of Cuba had an abnormal disturbance amplitude enhancement in the fourth period before the earthquake,and then appeared a second enhancement phenomenon in the period of the earthquake,and the disturbance was negatively correlated.The earthquake in Maduo,Qinghai had an abnormal disturbance amplitude enhancement in the fourth period before the earthquake,and it continued until the period of the earthquake,and the amplitude reached the highest during the period of the earthquake,and the affected area was the widest.The abnormal disturbance amplitude decreased after the earthquake,and the affected area decreased.(3)Based on the θ-value method,a statistical analysis of earthquakes of magnitude 6 or higher worldwide from 2019 to 2021 was conducted.The earthquakes were divided into two regions,the northern and southern hemispheres,for research and analysis.It was found that during earthquakes,the main abnormal disturbances in the northern hemisphere would shift southward,while those in the southern hemisphere would shift northward.From the spatiotemporal statistical results,the first pre-earthquake disturbance phenomenon occurred 29 to 25 days before the earthquake in sea area earthquakes,followed by a release and diffusion phenomenon 29 to 20 days before the earthquake,and the most obvious earthquake disturbance phenomenon occurred during the pre-earthquake period.For land earthquakes in the northern hemisphere,the first abnormality occurred 19 to 15 days before the earthquake,and the most obvious disturbance occurred during the pre-earthquake period.Sea area earthquakes are more likely to observe pre-earthquake anomalies than land earthquakes.As the magnitude of the earthquake increases,the ionospheric abnormal disturbance caused by earthquakes of magnitude 7 or higher is significantly higher than that caused by earthquakes of magnitude 6 to 7,and the anti-interference ability is higher,making the anomaly easier to observe.Finally,the reliability of the electric field data of the CSES was verified by establishing an ionospheric electrostatic field model.The main innovations of this paper are as follows.(1)The C-value method,which describes the fractal characteristics of the electric field spectrum signal,was applied to the power spectral data of the electric field observed by the CSES.After verification using multiple typical earthquake examples,some shortcomings of the C-value method were addressed.A stable background field observation model was constructed to extract the disturbance amplitude of the spatial electric field above the epicenter relative to the background field.Finally,abnormal disturbances in the ionosphere before and after earthquakes were extracted.(2)The spatiotemporal evolution of the spatial electromagnetic field before and after global earthquakes with Ms ≥ 6.0 from 2019 to 2021 was studied.The statistical analysis was conducted according to the earthquake location and magnitude.The results showed that the abnormal space was consistent with previous results,and the time of abnormal appearance was advanced from about 15 days before the earthquake to about 20-24 days before the earthquake.This provides a data basis for subsequent research.