| Earthquake disaster is one of the natural disasters that have the greatest impact on human living environment and social life.The frequency of earthquake activity in China is relatively high,and it has a larger intensity and a wider range of distribution,resulting in serious disasters.Therefore,how to analyze and predict earthquake activities and reduce the damage of earthquake disasters to people's lives and property safety has become an urgent problem to be solved.Since observing that the ionosphere anomalies occur before earthquakes,monitoring,discovering and analyzing ionospheric changes has become a hot research topic in the direction of seismic analysis and prediction.As an advanced space observation technology,GNSS has the characteristics of all-weather,large-scale,high precision and low cost.It has been widely used in ionospheric exploration.TEC acquired by GNSS is an important physical parameter to reveal the regularity and characteristics of ionospheric space-time variation.At present,IGS(International GNSS Service)has established hundreds of GNSS base stations all over the world,and thousands of GNSS base stations have been established in the mainland of China.With the increase of GNSS base stations,it's quite useful to gain TEC MAP with high spatial and temporal resolution.Further development of ground-based GNSS ionospheric observation technology has also played a good role in ionospheric TEC research.Based on the theory and hardware foundation above,this paper firstly introduces the earthquake and its causes,ionospheric and ionospheric disturbances.Then it investigates the research status of ionospheric anomalies affected by earthquakes in China and abroad,and reviews the results of earthquake case studies on ionospheric effects at home and abroad.In addition,this paper also introduces the current theory of seismic-ionospheric coupling mechanism.Then,based on the theory above,using GNSS data and global harmonic function,a high precision global ionospheric TEC model is established.The IRI model simulation data are used to evaluate the internal and external coincidence accuracy of the model.The conclusion that the accuracy of the model is reliable as a whole and it can be used to detect ionospheric TEC anomalies before earthquakes.Then,using this model,the pre-earthquake ionospheric anomaly effects of earthquakes with magnitude 7 or more concentrated in the Qinghai-Tibet Plateau region of China are studied,and some preliminary conclusions about the characteristics of ionospheric anomalies before strong earthquakes are obtained.The results of statistical analysis of earthquake cases are as follows:1)Under the condition of stable space weather,ionospheric anomalies often occur several days before strong earthquakes,and both positive and negative anomalies are possible.The higher the magnitude,the larger the anomaly amplitude and the wider the anomaly area.2)The maximum ionospheric anomalous disturbance of the continent does not generally occur over the vertical direction of the future epicenter,but migrates along the magnetic line to the equatorial direction for a certain distance.3)The ionospheric anomalies caused by earthquakes can be observed simultaneously in the magnetic conjugate region.4)Unlike Liu's research on ionospheric anomalies before the Taiwan earthquake,the strong earthquakes in the Qinghai-Tibet Plateau are usually accompanied by obvious positive anomalies.It is presumed that Taiwan is an island,and the mechanism of seismic energy divergence reflected in the ionosphere is different from that in the Qinghai-Tibet Plateau.5)Most earthquakes are accompanied by positive anomalies,while only Lushan earthquake is accompanied by negative anomalies.It is presumed that the implicit fault occurred in Lushan earthquake,that is,the seismic fault zone occurred below the surface,and there was no obvious surface activity.This may lead to the formation of additional electric fields contrary to the general situation. |
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