基于GPS观测的同震电离层扰动现象及其与震源特征关系的研究

Since there are still some controversies over the preseismic ionopsheric disturbance study, and the sufficiently complex questions remain open on their physical mechanism currently，it is necessary to develop the coseismic ionopsheric disturbance (CID) research to understand the impact of earthquakes on the ionosphere more intuitively. Firstly, we focus on the variation features of ionospheric TEC (total electron.content) during several hours before and after some typical earthquakes based on GPS data. We attempt to model the TEC perturbation created by the acoustic wave caused by earthquake based on acoustic ray tracing and atmosphere-ionosphere coupling. From the observed and synthesized CID, the initial motion, waveform, period, amplitude, apparent velocity, directivity as well as wave source in near-field and far-field will be determined and analyzed. Further, we confirm that coseismic ionospheric signals do contain important information about the earthquake source, meanwhile, there are also some other factors controlling the CID parameters. Therefore, the tectonic (magnitude, focal mechanisms, co-seismic displacements, fault dip) and non-tectonic (magnetic field configuration, background ionospheric parameters, geometry of GPS-sounding) contributions in the ionospheric signature will be discussed one by one. The dependence of CID on filter methods is also taken into account. In consequence, we will provide a quantitative form among earthquake parameters, CID parameters and background geomagnetic and ionospheric parameters. Finally, we will examine the possibility to extract useful information on the rupture process of large earthquakes and the surface wave velocities in oceanic regions where seismometers are not available. It means that CID could probably serve as a new indicator of faulting sensitive to ruptures with timescale up to several minutes. Our researches follow the hot issues and are of great scientific significance. The results will establish the relationship between the ionosphere signals and seismological information, and promote the development of the lithosphere -atmosphere - ionosphere coupling theory.

目前震前电离层扰动研究机理尚不明确，加强对同震电离层扰动（CID）的研究，有利于揭示地震对电离层影响的物理机制。首先，在陆态网络等数据支持下，基于GPS观测的电离层TEC变化，获取大地震的CID在近场和远场的初动、振幅、周期、速度、方向性等参数；结合地磁场、大气波动等数据，从地磁场形态、空间天气、GPS几何学等方面，确定同震激发的大气波场（声波、重力波、Rayleigh波）传播模式，辨析CID产生、传播和演化的机理，分析影响CID的非构造因素。然后，选取典型震例，分析海啸和陆域地震CID特征和波源的异同；比较逆冲、走滑和正断型地震的CID异同；分析断层走向对CID方向性的影响；讨论同震地表垂直和水平位移对CID振幅的贡献。最后，探索CID有效信息与发震断层、同震位移等的关系。研究内容紧贴国际前沿，研究结果将建立电离层信号与发震断层性质的联系，为岩石圈-大气层-电离层耦合理论发展提供支持。

地震、海啸等自然灾害可以产生大气声重波，将能量从地壳传播到大气层以及电离层高度。GPS等观测技术的发展为地球各圈层耦合的研究提供了有力的工具。本项目围绕典型地震的同震电离层扰动（CID）现象，基于地基和掩星GPS 的观测，开展了广泛的研究。研究证实了小波变换等时频技术对从地基和掩星GPS数据中提取CID信息的有效性。获取了CID在近场和远场的传播振幅、周期、走时、速度和方向性等参数；尤其是基于掩星数据分析了CID在垂直方向的结构和传播特征，对CID形态学是重要的补充。辅助地磁场、地震波等其他数据，分析了CID的各类影响因素，包括GPS观测几何、地磁场位型、中性大气风场以及构造特征。基于包含固体、海洋和大气的地球模型，模拟有限断层模型产生的各类波动在各圈层的传播，证实了观测的可靠性。报道了地震/海啸后在平流层高度长时间稳定存在的大气波动信号，分析了固体地球和大气耦合作用，证实了地震/海啸后波动在全大气中的可观测性。研究结果发展了基于掩星数据提取电离层扰动信息的技术，提升了电离层地震学相关内容的认识水平，促进了岩石圈-大气层-电离层耦合理论的发展，在海啸预警等领域有一定的应用前景。