Research On Ionospheric TEC Anomalies During Earthquake Based On Ground-based GPS Data

The ionosphere is the part of the earth's upper atmosphere that is ionized.Because of the particular nature of the ionosphere,solar activity,geomagnetic activity,and violent surface activities(earthquakes,volcanic eruptions)and other factors can cause ionospheric anomalies.The research on the mechanism of seismic-ionosphere coupling originated from the Great Alaska Earthquake in the 1960 s.In recent years,with the development of GPS observation technology,the study of seismic ionospheric anomalies has attracted more and more attention.However,due to the special physical properties of the ionosphere and the limitations of the observation data and the complexity of the earthquake,the study of seismic ionospheric anomalies is still limited.How to improve the detection method of seismic ionospheric anomaly and accurate extraction of ionospheric anomaly information has become a key issue that needs to be solved.Based on this,this article makes use of ground-based GPS data to discuss the periodic ionosphere variation law,anomaly detection method and seismic seismogram synthesis analysis.The specific content and analysis results are as follows:1.Two explanations of the seismic-ionospheric coupling mechanism are presented.The layered structure of the ionosphere,anomalous equator,and anomalous winter phenomena are described,and the influence of the space environment on the ionosphere is analyzed.2.In this paper,the ground-based GPS data is used to solve the ionospheric TEC process,and several key issues that should be paid attention to in the process of solving ionospheric TEC are described.The seasonal variation,diurnal variation and nonstationarity of ionospheric TEC were discussed using GIM grid data;the ionosphere was found to have significant equatorial anomalies and winter anomalies.3.The method of detecting ionospheric abnormality is analyzed.The accuracy of the background reference value of these models is mainly discussed by sliding time window method,sliding interquartile distance method,time series method and wavelet improved time series method.The experimental results show that among the four methods,the sliding time window has the lowest prediction accuracy;the sliding interquartile distance method takes second place,and the improved time series method based on wavelet improves the prediction accuracy compared with the traditional time series method.Although the accuracy of the improved time series method is approximately the same as that of the conventional method with the increase of the prediction time,the accuracy of the improved time series method is still high when detecting few epochs.4.Ground-based GPS data were used to analyze ionospheric disturbances during the three earthquakes in Kumamoto,Japan,Jiuzhaigou,and Mexico.The waveletmodified time series method was used to detect the TEC values in the seismogenic region.Under the influence of space environment,the ionospheric anomaly information related to the earthquake was screened,and the ionospheric TEC time series was performed temporally and spatially during the three major earthquakes.Statistical analysis,from different perspectives,judged the possibility of TEC anomalies during the three major earthquakes.The following results were obtained:(1)The majority of abnormalities occurred within 7 days before the earthquake and were basically positive anomalies.The larger the magnitude,the greater the anomaly was,and the abnormal time lasted more than 8 hours.(2)On the day of the earthquake,the correlation coefficient of each grid point dropped sharply,and the closer to the grid point near the equator,the stronger the influence of the earthquake on the correlation coefficient.(3)The anomalous area is not in the epicenter and is near the equator;similar abnormalities occur along the magnetic conjugated area.