Investigation On The Statistical Analysis And Electrical Structure Characteristics Of Geoelectric Field Seismic Anomalies

Many studies have shown that during the process of earthquake preparation and occurrence is accompanied by electromagnetic radiation.Therefore,the seismic electromagnetic observation method are considered one of the most likely geophysical methods to achieve the goal of short-impending earthquake prediction,which mainly includes the observation techniques of ground resistivity(apparent resistivity),geoelectric field,geomagnetic field and magnetotelluric.As one of the important tools for earthquake prediction research,many researchers believe that geoelectric field seismic anomalies are a significant seismic short impending phenomenon,the statistical characteristics of geoelectric field seismic anomalies and the physical mechanism of their formation are still unclear,especially the correlation characteristics of geoelectric field seismic anomalies in the frequency domain.Although researchers have introduced the spectral analysis method of digital signal for the investigation,which make some progress in characterization of geoelectric field seismic anomalies in the frequency domain,it is also affected by some factors.If the statistical characteristics of anomalies in the frequency domain between geoelectric field observation data and seismic events can be studied from multiple frequency components,the results can not only enhance the availability of geoelectric field data,but also enhance the impact of geoelectric field data in earthquake prediction.In this paper,we used an improved shifting correlation method to analyze the correlation characteristics analysis of different frequency components of the geoelectric field with seismic events of different magnitudes,taking into account the frequency of the geoelectric field and the earthquake magnitude,for some geoelectric field stations using observations of up to 12 or 8 years.In the data preprocessing,factors such as epicentral distance,seismic energy,and different frequency of the geoelectric field are considered;and the electrical structural characteristics of the subsurface medium in the station area are combined to analyze the differential characteristics exhibited by the correlation statistics results.In addition,the impact of the number of seismic events on the correlation statistical results is simply explained by randomly increasing and decreasing the number of seismic events,and the reliability of the research results is enhanced by comparing and analyzing the telluric field dominant azimuth method with the statistical results of this paper using some typical strong earthquakes that have occurred in recent years as examples.Finally,the mechanism of tidally triggered earthquakes is cited,and the differential characteristics exhibited by different frequency components in the study results are discussed.The following conclusions were obtained from the analytical study:(1)It is verified that the shifting correlation method has strong applicability in the correlation characteristics between geoelectric field and seismic events,and the results show that the geoelectric field stations have strong response to seismic events that satisfy the selection conditions in the surrounding 400 km area.(2)Different frequency components of the geoelectric field show anomalies in the process of earthquake preparation and occurrence,and the frequency components that show anomalies are correlated with the earthquake magnitude: the high frequency components of the geoelectric field(3.4h,4h,etc.)show correlation anomalies with both equivalent magnitude sequences of seismic events,but the low frequency components(24h)show correlation anomalies only with the larger magnitude sequences of seismic events.In terms of the timing of the appearance of the anomalies,it is generally about 10-55 days before the earthquake.(3)The horizontal anisotropy of the subsurface medium will cause differences in the response characteristics of the anomalies in different measurement directions.When the electrical bathymetry results below the station are greater than 300 Ω·m,the response capability of the geoelectric field observation to seismic events is reduced.(4)The dominant azimuth anomaly of the low-frequency component(24h)of the geoelectric field is simultaneous with the statistical characteristics of the shifting correlation in the time of the anomalous appearance before the earthquake,which may be related to the fact that the seismogenic fault is subject to the mutual coupling of solar and lunar tides.The statistical characteristics of the correlation between different frequency components of the geoelectric field and seismic events,and their coupling characteristics with the electrical structure beneath the station,obtained from the research work of this paper,are not only useful for the analysis and research of moderate to strong earthquakes,but also expected to provide some experience and technical support for the selection of the best observation location of the geoelectric field station and the research of earthquake prediction.