Research Of Lithosphere-Atmosphere-Ionosphere Coupling Mechanism Related To Earthquakes

In recent year, results form satellite observation in the world show that outgassings, surface shaking, electromagnetic emission from earthquakes and so on can create disturbance in the ionosphere. Scientists around the world have been focusing on research of ionospheric precursors of earthquake, which could be the most important way of short-term and impending earthquake prediction. (Lithosphere-Atmosphere-Ionosphere Coupling Mechanism Related to Earthquakes)。The mechanism of how earthquake can create disturbance in the ionosphere is getting universal attention, which is called Lithosphere-Atmosphere-Ionosphere Coupling Mechanism Related to Earthquakes. Research about LAI Coupling Mechanism can provide evidence background for extracting earthquake abnormality from satellite observation. The way to study the coupling mechanism is based on experimental observation, theoretical analysis, numerical simulation and so on, among which numerical simulation is the most important one. Recently, study of the numerical simulation of LAI Coupling Mechanism related to Earthquakes in the world mainly includes simulation of DC electric field coupling, AGW coupling and electromagnetic coupling. Electromagnetic coupling is the only mechanism which does not need the interaction of different physical.Many satellites have recorded obvious VLF/ULF/SLF electromagnetic signal in the ionosphere related to earthquakes. France, America, and Russia all have launched seisimo electromagnetic satellites in succession, such as DEMETER/QuakeFinder/Compass-2, to monitor the change of the electromagnetic environment of the earth. The China Seismo Electromagnetic Satellite Program has been engaged. The research about ionospheric electromagnetic precursory related to earthquake before is mostly the analysis of satellites data, lacking of the theoretical study of numerical simulation. This thesis is the first in China to study of Lithosphere-Atmosphere-Ionosphere coupling mechanism related to earthquakes, which fill up the blank, and can support the China Seismo Electromagnetic Satellite Program theoretically also approve and initiate the seismo ionospheric test network. This main research methods, contents and conclusions are as follow:(1) From Maxwell equations in the anisotropical medium, we deduced the formula of reflection coefficients, transmission coefficients and refractive index of homogeneous unstratified ionosphere. The influence of the medium parameters such as wave frequency, incident angle, DIP, electron collision frequency and electron density has been analyzed. We found that just when the matrix of the ionosphere conductivity satisfies some definite relation, there can be electromagnetic waves propagating in the ionosphere. Also, it is easier for the wave to penetrate into the ionosphere for high frequency wave with small incident angle; the dispersion and loss is also small. It is hard for the wave to penetrate into the ionosphere when the electron density is big and collision frequency is small, and the dispersion and loss is also high. The propagation loss is smaller when the angle between the direction of the wave vector and geomagnetic field is smaller, that is to say, it experience smallest loss for vertical propagation. At magnetism equator where the magnetic inclination is 0°, the wave almost can not penetrate into the ionosphere.(2) On these bases, full wave method which combined propagation matrix method and Gram-Schmidt orthogonalize method together is used to solve the Maxwell equations in the horizontal stratified ionosphere with oblique geomagnetic field which is more close to physical fact. The radio wave propagation model in the ionosphere is constructed. The calculation results show that there are two characteristic waves in the ionosphere, and one is right-hand circular polarization wave which has small phase velocity and loss, the other is left-hand circular polarization wave which has the opposite properties. Arbitrary polarization waves at VLF band which penetrate into the ionosphere will meet polarization reversal and turn to be stable left-hand and right-hand circular polarization. The radio waves experience the strongest attenuation in the D layer and are very unstable for the serious collision between charged particles and neutral particles. The left-hand circular polarization wave which is absorbed severely in the D region is called non-penetrating mode, and the right-hand circular polarization wave is penetrating mode. It can be concluded that the attenuation is mainly due to the collision between particles. Lastly, the vertical Poynting flux increases as the wave frequency decreases, which certificate that the lower frequency wave radiated from the earthquake is possible to penetrate into the ionosphere and be observed by the satellite.Comparing with the homogeneous unstratified ionosphere model, it can be concluded that the stratified ionosphere model is needed to demand the quantitative calculation accuracy.(3) The radio wave propagation model below the ionosphere uses 3D spherical earth-ionosphere wave guide model, which is combined with the full wave method of ionospheric wave propagation models to construct the LAI electromagnetic coupling model. With the help of the VLF signal transmitted by Australian long wave navigation station, the field in the ionosphere is calculated to verify the LAI electromagnetic coupling mechanism related with earthquakes constructed in this thesis. The results show that the concentric circles are caused by interference of VLF waveguide modes in the Earth-ionosphere waveguide. The main asymmetry exists about the east-west line, because the wave propagates toward the north along Earth·s magnetic field line, as expected. The center of these circles maps to the location of the VLF transmitter on the ground, the latitudinal displacement being due to the direction of the group velocity of the VLF waves. The offset is decided by the latitude of the transmitter. Comparing the calculated result and observed data, we found that: the calculated result is bigger than observed data generally. This maybe caused by the random irregularities in ionosphere, which scatter the radio wave and cause the loss of energy. The finite layer may also be the reason. The systematic error for idealizing the source to be vertical dipole may be another possible reason.Through the above studies, we found that it is easier for the lower frequency radio wave radiated by earthquake to be received by satellite in the ionosphere which is agree with the results of the foreign expect and the satellite observation. This result can provide the theoretical evidence for China Seismo Electromagnetic Satellite observation. And only vertical and right-handed polarization low frequency wave can penetrate into the ionosphere and received by the satellite. The probability to observe the abnormal at high latitude is bigger than the low latitude. The responding zone of the epicenter in the ionosphere has a latitudinal displacement along the magnetic line, the offset of which is due to the latitude of the transmitter. This regularity may help to find out the locations of the earthquakes.