We conduct a global analysis of GRACE-reconstructed gravity gradients from July 2004 to February 2011, to test whether the deep signals preceding the March 2011 Tohoku earthquake can be detected before the event as a specific feature originating from solid Earth. First, we improve the angular resolution of the gravity gradients using two overlapping ranges of azimuthal sensitivity to investigate short-term signals of large amplitude aligned with the orientation of the Northwestern Pacific subduction. Then, we set-up a method to identify consistent solid Earth signals shared by different GRACE gravity models. Robust signals in a model are selected based on their spatial overlap and relative intensity with the signals of another model, so that their sensitivity to the GRACE data processing and ocean dealiasing product can be tested. We show that the dipolar gravity gradient anomaly before the Tohoku earthquake is nearly unique in space and time in the GRACE GRGS03 solutions. A well-resolved dipolar spatial pattern, typical of dislocations within the solid Earth and poorly sensitive to the ocean dealiasing model, is detected. In addition, the preseismic gravity gradient increase is highly consistent between the GRGS03 and CSR06 solutions, independently from their respective oceanic corrections, and can be clearly distinguished from rare anomalies of similar amplitudes all associated with the water cycle over continental areas. Our approach offers solutions for the continuous monitoring of the Pacific subduction belt to document transient slabs motions in real time from global satellite gravity fields, and their relation with shallower deformations and seismic events.

中文翻译：

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在 GRACE 重力解决方案中检测震前信号：在 2011 年东北 Mw 9.0 地震中的应用

我们从 2004 年 7 月到 2011 年 2 月对 GRACE 重建的重力梯度进行了全球分析，以测试 2011 年 3 月东北地震之前的深层信号是否可以在事件发生之前作为源自固体地球的特定特征被检测到。首先，我们使用两个重叠的方位灵敏度范围来提高重力梯度的角分辨率，以研究与西北太平洋俯冲方向一致的大振幅短期信号。然后，我们建立了一种方法来识别不同 GRACE 重力模型共享的一致固体地球信号。一个模型中的鲁棒信号是根据它们与另一个模型的信号的空间重叠和相对强度来选择的，从而可以测试它们对 GRACE 数据处理和海洋去混叠产品的敏感性。我们表明，在 GRACE GRGS03 解中，东北地震前的偶极重力梯度异常在空间和时间上几乎是唯一的。检测到了一个很好分辨的偶极空间模式，它是固体地球内典型的位错，对海洋去锯齿模型不敏感。此外，GRGS03 和 CSR06 解之间的震前重力梯度增加高度一致，独立于它们各自的海洋校正，并且可以清楚地区分与大陆地区水循环相关的振幅相似的罕见异常。我们的方法为太平洋俯冲带的连续监测提供了解决方案，以实时记录来自全球卫星重力场的瞬态板片运动，以及它们与较浅变形和地震事件的关系。