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主要研究利用GRACE(重力恢复和气候试验)卫星恢复的时变全球重力场计算2004年12月26日苏门答腊大地震引起的同震和震后重力的变化。进而对于一个自重、弹性、球状分层的地球模型,利用简正振型叠加法比较观测到的同震重力变化制作它的完全弹性引力响应模型。需要特别关注海洋质量重新分布的影响。在对数据进行反演时要注意,海洋潮汐模型的误差及陆地水文和大洋环流产生的季节性和周年性信号会导致构造重力的变化,也就是要消除同震重力变化受到震后松弛的影响。我们使用了由测地空间研究组(GRGS)提供的4.6年时间尺度的全球重力解数据,其中包括震后26个月的数据。为了相互比较,也研究了空间研究中心(CSR)提供的用频谱窗或高斯空间平滑处理后的Release-04解。结果均以大地水准面高变化和重力变化给出。从两种不同的重力解计算的同震和震后重力变化在全球范围上是相似的,但它们的空间幅度和振幅与对GRACE重力场滤波处理时使用的滤波器种类相关。使用测地空间研究组解数据的信噪比最大。相比同震信号,震后信号的频谱含量更接近GRACE的带宽,因此能被GRACE卫星更好地观测到。在安达曼海巽他海沟以东,同震信号表现为重力明显减少的趋势。在该海沟以西,重力有小幅的增加。同震重力变化的模型与GRACE卫星数据计算出的重力信号相比,在总体形状和取向、相对于海沟的位置和量级上都非常吻合。同震重力变化后会出现震后松弛,该松弛可以用一个平均松弛时间为0.7年的指数增函数描述。总的震后重力变化的特征呈现出大范围的正异常,且主要分布在海沟正上方和沿着俯冲带扩展15个纬度。26个月后,同震重力的减小被震后松弛部分补偿,但在普吉岛南部依然有负异常出现。海沟西部15个纬度范围内的重力都是增加的,最大值出现在震中南部地区。通过研究分析两种全球水文模型和一种大洋环流模型,显示我们利用GRACE卫星对同震和震后重力变化做出的估计几乎没有因俯冲带和安达曼海中部地区的陆地水和大洋环流年度变化而产生偏差,而在马来半岛则产生了几微伽的偏差。
The main study uses the time-varying global gravity field of GRACE (gravity recovery and climate test) satellite restoration to calculate the coseismic and post-earthquake gravity changes caused by the Sumatra earthquake on December 26, 2004. Furthermore, a complete elastic gravitational response model is developed for a gravity, elastic and spherical layered earth model by comparing the observed coseismic gravity changes with the simple zenith superposition method. Special attention needs to be given to the impact of the redistribution of ocean quality. When inverting the data, note that errors in the ocean tidal model and seasonal and annual signals from terrestrial hydrology and ocean circulation lead to changes in tectonic gravity, that is, to eliminate the effects of post-seismic relaxation on the coseismic gravity changes . We use the 4.6-year global scale data provided by the Geodetic Space Group (GRGS) on a time scale of 26 months, including data for 26 months after the earthquake. In order to compare with each other, the Release-04 solution obtained by Spatial Research Center (CSR) after smoothing with spectral window or Gaussian space is also studied. The results are given by the high geoid and gravity changes. The coseismic and post-earthquake gravity changes calculated from the two different gravitational solutions are similar globally but their spatial amplitudes and amplitudes are related to the types of filters used for GRACE gravitational field filtering. The signal to noise ratio using the geodetic spatial group solution data is the largest. Compared to co-seismic signals, the spectral content of post-earthquake signals is closer to the GRACE bandwidth and can therefore be better observed by GRACE satellites. To the east of the Andaman Sea, Tau Trench, the coseismic signal shows a marked reduction in gravity. To the west of the trench, there was a slight increase in gravity. The model of coseismic gravity change is in good agreement with the overall shape and orientation, relative to the location and magnitude of the trench, as compared with the GRACE satellite data. Post-earthquake relaxation occurs after a coseismic gravity change, and the relaxation can be described by an exponential function with a mean relaxation time of 0.7 years. The features of the total post-earthquake gravity changes show a wide range of positive anomalies, and are mainly distributed just above the trench and extending 15 latitudes along the subduction zone. After 26 months, the reduction of the coseismic gravity was compensated by the relaxation part after the earthquake, but negative anomalies still occurred in the southern part of Phuket. In the western part of the trench, the gravitational force increased in the range of 15 latitudes and the maximum appeared in the southern part of the epicenter. By studying and analyzing two global hydrological models and a model for ocean circulation, it is shown that the estimates of coseismic and post-earthquake grav- ity changes we make using GRACE satellites are almost unchanged due to subduction zones and terrestrial water and ocean circulation in the central part of the Andaman Sea Changes in the deviation, and in the Malay Peninsula has produced a few micro-gamma deviation.