| In view of geodynamic background, seismogenic environment and triggering mechanism of strong earthquake not fully understood or mastered yet, the empirical prediction based on precursory information has been a major idea of seismic monitoring and forecasting. The tracking observations of a variety of geophysical anomalies, such as anomalies related to ground surface deformation, geoelectricity, geomagnetism, geochemistry, underground fluids, have been the traditional seismic monitoring techniques. Through these techniques, our knowledge of the earthquake preparation process has reached a new level. Moreover, the certain achievements have also been made in the mid- and long-term earthquake prediction. Even so, our knowledge and understanding of seismic precursors still remains immature due to the imperfection and complexity of earthquake theory. Because of this, it is difficult to make a substantive breakthrough in short-term and impending earthquake prediction which can bring the most significant benefits in disaster mitigation.As the Earth is a giant system consisting of multiple spheres, there must be transport and exchanges of substance and energy between those spheres. As an important part of the near-Earth space, the ionosphere is bound to interact closely with the atmosphere and lithosphere beneath it. And earthquake, as a product of the vigorous plate motions within the lithosphere, will inevitably clamp down on the state of the atmosphere, which acts on the ionosphere in turn. Such linkages between the spheres provide a way for us to discern the Nature and understand the Earth's events from space. This interaction, obviously, also makes it possible for us to seek information on the earthquake preparation activities from the ionosphere. So far, the disturbing phenomenon of preseismic ionospheric anomalies has been confirmed by a large number of observations. Despite all that, however, there is still no general and proven consensus of earthquake-atmosphere-ionosphere coupling mechanism.In order to explore the characteristics and rules of preseismic ionospheric disturbances, and reveal the inherent seismic-ionospheric coupling mechanism, detection and analysis of seismic-ionospheric effects was made in this paper on strong earthquakes (Ms?6.0) in Chinese mainland using VTEC time series data derived from ground-based GPS observation. Subsequently, the representative theories of seismic-ionospheric coupling mechanism were analyzed, and finally numerical simulation of coupling mechanism of additional vertical electric field radiation was carried out with the help of a physical ionospheric model. Some results and main conclusions are as follows:(1) Observations and inversion of the ionosphere. In the study of ionospheric observation techniques with ground-based GPS, the spherical harmonics function was used to achieve a high-precise inversion of regional VTEC, and an inversion method to calculate the VTEC over the GPS station by giving weight to the nearby VTEC are also proposed. As for the study of occultation technique with space-based GPS, spherical symmetry assumption of ionosphere is the dominant error in the classical Abel integral transform inversion. In order to overcome this limitation, an inversion method of ionospheric occultation based on the ionospheric horizontal gradient constraints was proposed, and highly accurate results were achieved. In view of the limitation of traditional ART algorithm, the method of adjusting appropriately the relaxation factor was proposed to accelerate the convergence of the iterative solution during the three-dimensional tomographic reconstruction of the ionosphere. In addition, a more binding algebraic convergence criterion is used to improve the precision of tomographic reconstruction. The development of ionospheric data assimilation model is currently the research focus in the field of ionospheric information acquisition. After analyzing the research at home and abroad, especially the results and progress made by the US counterparts, this paper tries to develop an ionospheric data assimilation model based on the Kalman filter technology. This model involves an ion, and assumes that the only ion is O+in the range of ionospheric height. The assumption decrease the difficulty of developing the ionospheric assimilation model, however, the loss of precision of electron density inversion is very little due to the fact that O+occupies absolute advantage in the quantity above the ionospheric E layer. In consideration of the features of several techniques of ionospheric information acquisition mentioned above, the monitoring requirements of seismic-ionospheric effects and existing observational resources, the ground-based GPS should be the ideal means of tracking observations of ionospheric anomalies. The detection and analysis of seismic-ionospheric effects are based on the ground-based GPS technology in this paper.(2) Characteristics and rules of seismic-ionospheric anomalous disturbances. Excluding the influence of non-seismic factors, such as mutation of the Sun-Earth space environment, this paper made the detection and analysis of preseismic ionospheric anomalies on strong earthquakes (Ms?6.0) in Chinese mainland during 2000?2014. Finally, the statistical results show that the preseismic ionospheric anomalies have the following characteristics:?For the vast majority of earthquakes, the positive or negative ionospheric anomalies near the epicenter which may be associated with earthquakes occur in a week before the earthquake.?Ionospheric anomalies area caused by earthquakes can extend beyond 10° in latitude and longtitude. The ratio of east-west and north-south direction is about 3:1 in the anomalous dimension. The abnormal zone often moves toward the equatorial direction.?The seismic-ionospheric anomalies appear mostly in the afternoon, last usually beyond 4 hours in the Chinese observation district, and drift from the east to the west.It is noteworthy that the impending properties of seismic-ionospheric precursors are especially prominent, which is the major advantage of seismic-ionospheric precursors over other precursors. But unfortunately, the preseismic ionospheric anomalies were not detected before some strong earthquakes through the analysis of earthquake cases in this dissertation, which fully illustrates the complexity and difficulty of the research on seismic-ionospheric effects. In addition, the research and analysis of the coseismic ionospheric disturbances (CID) from a representative earthquake shows that acoustic gravity waves stimulated by vertical ground displacement also triggered the ionospheric disturbances during its propagating upwards. In fact, the disturbance amplitude from this kind of CID is very subtle, which is usually observed in 10-15 minutes after the earthquake outbreak near the epicenter. Nevertheless, the-research about the characteristics of CID has a practical significance in determining the hypocenter parameters, understanding the crustal structure, and assisting the tsunami warning.(3) Seismic-ionospheric coupling mechanism. By investigating the research results about seismic-ionospheric coupling mechanism, the author thinks that the seismic-ionospheric disturbances are more likely to result from the additional vertical electric field in the seismogenic zone. As for the coupling mechanism, the theoretical interpretation clarified it to some extent. After introducing the theoretical ionospheric model SAMI2 in details, the model was used to make a simulation of ionospheric evolution under the action of additional electric field based on an actual earthquake. The results of simulation confirm that the additional vertical electric field radiation could be the source of the preseismic ionospheric disturbances, which provides a theoretical support for monitoring the seismic-ionospheric effects. |
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