Research On Methods Of Judgement For Geomagnetic Anomaly

The method of judgement for geomagnetic anomaly is an important branch of geomagnetism.Its main purpose is to predict earthquake from the view of geomagnetic anomaly,and to provide effective basis for earthquake prediction.The software of geomagnetic analysis and prediction which developed by Jiangsu Earthquake Agency is the main tool for judging geomagnetic anomalies in China at present.According to statistics,the accuracy of earthquake prediction by using the software to judge geomagnetic anomaly is about 50% nowadays.This value is far from providing accurate correspondence between the geomagnetic anomaly and the earthquake,while the methods of singular spectrum analysis and ARMA fitting model are much more effective in enhancing original data features and removing noise.Therefore,this paper starts with researching into the theory about the software of geomagnetic analysis and prediction,and studying the operation means and performance of the methods in geomagnetic anomaly judgement.Combining the methods of singular spectrum analysis and ARMA fitting model with the method of geomagnetic anomaly judgement,using the method of numerical fitting to make the original sequence reconstructed.Then realizing the traditional method of geomagnetic anomaly judgement optimized,improving the reliability of earthquake prediction and providing a new way for obtaining the accurate correspondence between geomagnetic anomaly and earthquake prediction.The background of this research is the M5.7 Earthquake in Songyuan on May 28,2018,which is based on the geomagnetic data collected by 11 national geomagnetic observatory stations,including Sangang Seismic Station,Tonghua Seismic Station,Dalian Seismic station,Yingkou Seismic station,Dedu Seismic station and its like.The main contents of this paper are as follows:1.7 kinds of traditional methods in geomagnetic anomaly judgement are used to study in geomagnetic anamoly judgement,which including the method of adding and unloading response ratio,harmonic amplitude ratio,day-to-day ratio,spatial correlation of daily variation,low-point displacement,one-value-per-day difference and superimposition of anomalies.The object of this research is pre-processing minute value data of geomagnetic components called Z,H,D and F,which are from June 1,2017 to December 31,2018.It turns out that the other 6 methods all show out geomagnetic anomalies in different degree before the Songyuan M5.7 earthquake except the method of spatial correlation of daily variation.2.Achievement on method of day-to-day ratio for anomaly judgement based on singular spectrum analysis.According to the steps of constructing track matrix,decomposing sequence and reconstructing sequence,the geomagnetic components are fitted by using singular spectrum analysis.The accuracy of the fitting method is high,and the changing trend of the fitting sequence is consistent with the original sequence.In light of that we use the singular spectrum analysis to make the day-to-day ratio sequence fitted,and get the conclusion that the trend of day-to-day ratio sequence is much more obvious and the effective components are more concentrated than the original sequence.The threshold line is set according to the average ± 2-time mean square deviation,and the results of the above include the results outputted by the original method,and also the conditions of over-threshold are denser in the vicinity of the Songyuan M5.7 earthquake.The results show that the method integreted singular spectrum analysis with day-to-day ratio could extract the geomagnetic anomaly accurately,and the anamaly judged by this method can be used as an indication about the characteristics of geomagnetic anomaly before earthquakes.3.Achievement on method of day-to-day ratio anomaly judgement based on ARMA fitting model.According to the processes below to create ARMA fitting models for original sequence,which including stationarity test,analysis of both autocorrelation and partial autocorrelation,judgement for type of the model and decision of order in the model.The fitting curve could present the variation characteristics of the original series directly,and it confirms that the ARMA model has relatively high fitting precision.The ARMA fitting model of day-to-day ratio series show that the fitting curve is more concentrated than the original curve.The threshold line is set as average value ±2-time mean square deviation.The results of the above-threshold day include the results processed by the original method,and the anomalous phenomena are denser in the vicinity of the Songyuan M5.7 earthquake.The results above show that it has significant meaning in extracting day-to-day ratio by ARMA fitting model,and the result could be used as an premonition before the M5.7 earthquake in Songyuan.