Investigation On The Statistical Characteristics Of Geoelectric Field Seismic Anomalies

Seismic electric signals(SES)is widely recognized as a significant seismic prognostic signal,but there are also difficulties in identification and application.on the one hand,the complexity of the seismic incubation process and its physical mechanism is still unclear;on the other hand,the diversity of the SES forms,and there are a series of complex and variable phenomena such as anomaly before earthquake,earthquake without anomaly,and anomaly without earthquake in actual observation.In recent years,researchers have transplanted and improved a variety of geoelectric field(GEF)seismic anomaly extraction methods and conducted more in-depth retrospective analysis studies on influential earthquakes.there is still no consensus on the statistical characteristics of geoelectric field anomaly signals that are deterministically associated with earthquakes.For a typical earthquake,GEF anomalies may occur before,during,and after the earthquake.However,due to aftershocks or other earthquakes,the anomalous signals are often superimposed on each other and may even be mixed with interfering signals.These interferences make it difficult to accurately describe the relationship between earthquakes and GEF from retrospective study results of single or few earthquakes.With the increase in the number of earthquakes,the accumulation of observations,and the introduction of the shifting correlation method(SCM),It is possible to study the statistical characteristics of seismic anomalies in GEF.The results can fully demonstrate the seismic anomalies of the GEF before and after the earthquake,and reveal the correlation and spatial and temporal distribution characteristics between the earthquake and GEF.In this paper,we use an improved SCM to calculate the observations of 18 GEF stations located on the major seismic belts in Chinese mainland for the past 12 years.The seismic events and the epicenter distances of the stations,as well as the seismic belts where they are located,are taken into account in the calculation.The reliability of the statistical results is finally verified by distinguishing different seismic energies and adding random earthquakes.In addition,the results of dominant azimuth and daily mean waveform changes are compared with the geoelectric field anomalies of typical earthquake cases in this paper,which greatly improve the reliability of the statistical results.During the study,the GEF stations in mainland China are divided into three categories.The first category is the case where there are few fault belts around the station or seismic events near the station are all concentrated in a certain fault belt(e.g.,Wushi,Taiyuan,etc.).The second category is in the intersection of two different strike fault belts or stations near the station earthquake distribution in two different strike fractures(e.g.,Chengdu,Longnan,etc.).The third category is stations in complex fracture distribution or stations located in fractures without concentrated earthquakes(e.g.,Yanyuan,Wenquan,etc.).The following conclusions are drawn from the systematic analysis: 1)Study proves that the SCM can effectively analyze the correlation between GEF and earthquakes 2)Both Type I and Type II GEF stations in the paper have good monitoring of earthquakes around them,and most of the anomalies appear 15-40 days before the earthquake(3)For the second type of stations and the selective phenomenon exhibited by different measurement results of the same station,it may be related to the distribution of the fault belts and the subsurface electrical structure,and the possibility of observing seismic anomalies is greater when the local stations are on the same fault as the earthquake(4)In addition,combining with some existing geomagnetic bathymetry results,the characteristics of the electrical structure beneath the measurement area of seismically sensitive GEF stations are initially explored,and it is believed that when the measurement area is located on the resistivity boundary,it is easier to observe the anomalous changes of GEF.The statistical characteristics obtained from this research work can not only provide technical guidance for the extraction of information related to seismic anomalies in GEF observation stations,but also provide technical support for the site selection and construction of GEF stations and more comprehensive research on seismic GEF phenomena and mechanism exploration.