Research On Anomaly Characteristics Of Electromagnetic Radiation Signal And Mechanism Before Strong Earthquakes

Earthquakes in the preparation and occurrence process often produce low-frequency electromagnetic radiation.The seismo-electromagnetic radiation anomaly means certain electromagnetic signals released by electromagnetic radiation source which generated with seismogenic processes.Its main causes are piezoelectricity,piezomagnetism and electrokinetic effect,etc.Some scholars,in the zero magnetic space during the process experimental study of rock fracture,recorded that in rock failure process it does have a low-frequency electromagnetic radiation.Since direct electromagnetic radiation from the source of information,a low frequency electromagnetic skin depth is greater than the focal depth,the skin depth depends on the frequency and dielectric electrical structure,before the earthquake probability of the observing low frequency electromagnetic radiation from seismogenic zone is big.In addition,the low-frequency electromagnetic waves from the earthquake area is minimal attenuation to the ground,so that it can carry microfracture information source areaand generally appeared in the late earthquake preparation.Therefore,it has promising approach of short-term prediction earthquake.In the paper,based on the observation data of terrestrial digital electromagnetic stations and the data of space electromagnetic satellite of China,I collected more than 100 digital electromagnetic station observation data,and the station data quality classification assessment.The observation data is used to analyze pretreatment,identify and eliminate the influence of various non-seismic disturbances of ground and space,and then,the electromagnetic anomaly information extraction method,such as Hilbert-Huang transformation,polarization analysis,polarization principal axis calculation,normalized variation rate method and dynamic spectrum analysis,is used to study the typical strong earthquake events in the Chinese mainland,extract the real electromagnetic radiation signal before the strong earthquake,summarize and analyze the various waveforms,spectral characteristics and field intensity changes of electromagnetic radiation before the earthquake.And establishing theoretical basic electromagnetic wave model,exploring the abnormal seismic electromagnetic radiation signal generation,propagation and spreading mechanism,conducting truly disaster-reduction effective scientific research,providing reference decision for the follow-up strong earthquake prediction,especially short-term prediction,and improving earthquake precursor monitoring capabilities.Through Hilbert-Huang transform(HHT)method,we found that the D component of geomagnetic field varies significantly three months before an earthquake.The polarographic analysis further showed an elevation tendency and an amplitude increase before most earthquakes.The study of the earthquake electromagnetic field model indicates the phrasal characteristics of electromagnetic radiation anomalies in both time and frequency,which follows the laws of earthquake preparation and occurrence.This paper also studied the separation of onternal and external field source of geomagnetic field and the inversion of equivalent current system.These indicate that the variations between latitude deviation of current focus and the geomagnetic lowest shift are synchronized.By the normalized variation rate method,this paper performed calculation on the anisotropic apparent resistivity of earthquake fracture zones before Wenchuan and Yushu earthquake.The susceptibility difference among relative observation positions to the fracture zone reveals the fact that anisotropic variation of apparent resistivity is more significant on(or near)the seismic fracture zone.The study of 6 orbits of Demeter satellite before Wenchuan M8.0 earthquake revealed that several components of electromagnetic fields enhanced in various degrees.We further discovered that 50-300Hz is the dominant band of earthquake-related ionospheric effect.The more closer the special position is,the better.And the directions of the anomalies are different among earthquakes in different hemispheres.