Research On Coseismic Ionospheric Disturbances Based On Ground-based GNSS

Outbreaks of natural disasters,such as earthquakes,usually cause ionospheric disturbances.Based on GNSS-VTEC technology,the disturbance characteristics and variation regularity of co-seismic ionospheric anomalies are analyzed,and the underlying mechanism is explored,which is of great scientific significance for seismic monitoring.The paper uses ground-based GNSS data to study the the ionospheric disturbance characteristics and variation laws of earthquakes in New Zealand and Nepal,which are located in the southern and northern hemispheres respectively,and deeply analyses their common characteristics,and verifies the results by the Chilean earthquake in the southern hemisphere.The main contents and results of the study are summarized as follows:(1)Using the dual-frequency carrier phase observation to obtain the VTEC during each earthquake occurrence,we analyzed its disturbance variation,and this paper used the 4th order 2-8MHz bandpass filtering method to remove the ionospheric disturbance trend term interference.Finally,using a variety of perturbation feature analysis methods,such as VTEC time series analysis,two-dimensional perturbation feature analysis,disturbance velocity analysis,wavelet transform spectrum analysis and disturbance azimuth analysis,etc.,the coseismic ionospheric anomalies of each earthquake Common features were analyzed.(2)Through the analysis of the VTEC spatio-temporal variation during the earthquake,it is shown that the time and disturbance amplitude of the coseismic ionospheric disturbance are related to the epicentral distance of the disturbance.The ionospheric disturbance in the vicinity of the epicenter occurred about 10?15 minutes after the earthquake.With the increase of the epicentral distance,the disturbance appeared to lag several minutes after the disturbance near the epicenter.At the same time,there exists an asymmetry of disturbance between the northern and southern hemispheres.The disturbance in the north of the relative epicenter is not obvious,and the disturbance of the southern hemisphere earthquake is not obvious in the south of the relative epicenter.(3)The characteristics of disturbance propagation velocity and spectral relationship change indicated that after the earthquake,different types of disturbances were excited by different disturbance sources and then appeared in the ionosphere,with diverse characteristics.The vertical and upward acoustic heavy waves are generated by the source.Or the second ionospheric disturbance trend term interference sound waves are caused by Rayleigh waves away from the source area.(4)There are multi-directional disturbances near the epicenter,and there is a main disturbance direction,that is,there are two propagation directions in the vicinity of the epicenter.The propagation of the main disturbance direction is more obvious than that of the other direction.The main disturbance propagation path and the earth plate are related to the sideline.