| With the development of technology in observing the earth from space,observing data with man-made satellite to study electromagnetic precursory anomaly had been a new method of concern.Especially after the launching of France's”DEMETER”,Experts in the field of seismology at home and abroad had been carried out a lot of research about seismic ionospheric disturbance based on the phenomenon of the data from DEMETER,and put out“lithosphere-atmosphere-ionosphere” coupling mechanism,which provided a theoretical basis for Ionospheric disturbance before earthquake.A large number of research results showed that,there did have electromagnetic anomalies before earthquake,especially the strong earthquake,which could be caught by satellite and ground station.It would be more convenient to gain the full range of those three-dimensional abnormal circumstance's changing information before strong earthquakes when we analyze with those observing data from space station and ground station.This article would give the conjoint analysis of the data in Wenchuan Earthquake by using moving average method,kurtosis method and wavelet time-frequency analysis,which from DEMETER 's ULF electric field waveformIV and geoelectric field observation data of ground station.Space observingstation had studied the ULF three component waveform data of electric field(ascending orbits)of Wenchuan Earthquake's first three revisit period(3.26-5.12),the research area was a taking Wenchuan as the centre of circle and with a radius of 10 degrees' circle.The ground observing data mainly chose lugu lake,yanyuan,hongge's observation data of the minute value of the geoelectric field in the 42 days before earthquake.The contents and results of this study were as follows:1)Moving average method could remove background field information of geoelectric field data to a certain extent,so that the electromagnetic disturbance information before earthquake could be more prominent.For space-based electric field data,moving average method removed DEMETER's ULF data's large scale V×B induced electric field,to study of small scale electric field disturbances possibly caused by earthquakes and other factors.When it came to ground electric field data,moving average method eliminated the influence of tidal and natural electric field is eliminated to a certain extent.2)It was obviously to discover that the amplitude variation of kurtosis anomaly in the third cycle(4.27-5.12)was more intense than in the previous two cycles by studying peak-to-peak characteristics of small-scale disturbance data of spatial electric field in the first three revisit periods before earthquake.After summarizing the results of previous studies using DEMETER satellite to analyze the Wenchuan earthquake,discovering that the anomalies of Wenchuan earthquake occurred in the range of about 10 days before the earthquake,that was,the third cycle.Further study of the third cycle perturbation data revealed that,there were three anomalous orbit,and the range of anomalous disturbances was mostly between geomagnetic latitude10 degrees north latitude and 30 degrees north latitude,especially in the area south of the Wenchuan earthquake epicenter.3)Corresponding space-based ULF electric field,there were three types of variation in the ground electric field.Before the Wenchuan earthquake,waveform distortion(low frequency),background jump,high frequency jump appeared in the ground electric field,the period of variation occurred from April26 to May 12,which was consistent with the time of space-based electric field.4)Wavelet time-frequency analysis was used to analyze the field data from the angle of time-frequency.It was found that the local energy of wavelet energy spectrum increased in the low frequency components of the field data(space base: < 0.5 Hz,foundation: < 0.005 Hz)on May 11,the day before the earthquake,and it was consistent in time. |
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