Extraction And Correlation Study Of Magnetic Declination Anomaly Information In Geomagnetic Station Records

In view of the current doubts about the correlation between geomagnetic anomalies and earthquakes and aiming at the various methods of coseismic geomagnetic anomaly research ressulting in different effects of the extraction of anomalous signals,this paper takes the geomagnetic data recorded by domestic geomagnetic stations as the research object,established the IAGA(International Association of Geomagnetism and Aeronomy)observation data model of the magnetic declination component of the geomagnetic station and adopted a co-seismic geomagnetic anomalies correlation analysis method,which can quickly and effectively extract the data of geomagnetic declination anomalies during large earthquakes and perform correlation analysis to explore the correlation between geomagnetic anomaly signal and large earthquake,so as to provide a new method for the study of large earthquake prediction.This paper analyzes the decomposition model of geomagnetic field.The internal field of the basic geomagnetic field accounts for the main part is relatively stable,while the changing magnetic field including the disturbance change is relatively small.The intensity of the largest magnetic storm only accounts for a few percent of the basic magnetic field strength and has little effect on the magnetic declination.The research in this paper suggests that part of the internal field of the changing magnetic field is the abnormal changing magnetic field caused by the geomagnetic effect inside the earth before and after the earthquake.It is the new changing magnetic field generated in the process of micro fracture and expansion of rock medium in the focal area and plate edge before and after the release of the energy of a large earthquake.The magnitude of change before the earthquake is small,and with the arrival of the earthquake wave,the magnitude of change becomes the largest during the earthquake.The amplitude of variation is much higher than the magnetic disturbance of the external source field.The changing magnetic field has the characteristics of appearing in multiple places at the same time.Geomagnetic anomalies of magnitude 7 and above can occur in areas more than 2000 km away from the epicenter,and will not be delayed by more than ten days,but like the location near the epicenter.Thus,the IAGA geomagnetic data set of the geomagnetic station,the observation data model of the magnetic declination component,and the correlation analysis data set of the magnetic declination abnormality of the geomagnetic station were established.In this paper,an algorithm which can effectively eliminate the non-seismic anomaly data is adopted and implemented through Python Programming to solve the problems such as empty files and damaged files exist in the geomagnetic data files,some files have incomplete data,and there are some continuous and identical non-seismic anomaly invalid data with very large values;This paper uses the sliding maximum difference method to carry out statistical analysis of declination D data,effectively eliminating the influence of background field;the data in seconds is processed and analyzed using the declination difference ratio and continuous threshold method.The condition of abnormal file and the condition of abnormal recording are given.The abnormal magnetic declination with large difference amplitude and long duration was extracted and recorded to the ?D abnormal data set,reconstructed the ?D abnormal correlation analysis data set.Combined with seismic theory and correlation analysis,the correlation between magnetic declination anomaly and seismic magnetism is analyzed.Finally,a co-seismic geomagnetic anomalies correlation analysis method is summarized.In the end,the co-seismic geomagnetic anomalies correlation analysis method is validated by the data of IAGA-2002 seconds-level relative observation preprocessing of nearly 80 geomagnetic stations before and after 5 earthquakes of magnitude 7 and above in China since Wenchuan earthquake.The results showed that:(1)During the 5 large earthquakes,some geomagnetic stations far away from each other have recorded geomagnetic anomaly data,which are likely to be coseismic anomalies of large earthquakes;(2)The epicenter was near a geomagnetic station where geomagnetic anomaly data were recorded;(3)Among the geomagnetic anomalies,the declination D anomaly is the most obvious;(4)The anomaly of magnetic declination D is characterized by high amplitude,high frequency and short duration of the difference of magnetic declination ? D.(5)The correlation coefficients of magnetic declination difference anomalies of three or more stations are greater than 0.9.The results show that the co-seismic geomagnetic anomalies correlation analysis method can find the geomagnetic anomalies during 5 earthquakes with magnitudes over 7 in China since Wenchuan earthquake.During large earthquakes,the higher the magnitude,the more co-seismic anomalous stations,the larger the value,and the easier it is to be observed the geomagnetic anomalies.Coseismic geomagnetic anomaly correlation analysis method integrates all geomagnetic stations and all large earthquakes that can be obtained into correlation analysis,overcomes the deficiency that conventional analysis methods usually only aim at a certain local area or a certain earthquake case,and is easier to find the correlation between geomagnetic anomalies and large earthquakes,thus having higher reliability.If the geomagnetic data recorded in seconds can be obtained in real time,and the millisecond or microsecond data at the time of the anomalies can be further obtained,a new method for prediction of large earthquakes is expected to be provided.