The Far Reach of Megathrust Earthquakes: Evolution of Stress, Deformation and Seismicity Since the Sumatra-Andaman Rupture

2004年12月26日的苏门答腊-安达曼地震是20世纪60年代以来最大的地震，也是现代空间大地测量学和宽带地震学时代发生的第一次9级地震。这次地震在距离达4500公里的地方产生了可测量的静态地表位移。鉴于2004年地震的巨大规模，a ？第二波?软流圈加速流的发展将对区域形变场造成几十年的扰动。此外，局部余震、孔弹性回弹等震后变形过程也会影响区域变形场。事实上，苏门答腊-安达曼地震后最初几个月的形变测量结果可以很好地解释为，沿着断裂及其下方的局部余震的运动学模型，或粘弹性松弛。2004年的地震发生三个月后，在俯冲带的邻近部分发生了8.7级大地震，2007年又发生了8.4级地震。这个地震序列提供了一个难得的机会，从根本上提高我们对大逆冲断裂的地震周期以及相邻的海洋和大陆地壳和上地幔的组成特性的理解。研究小组从这项工作中获得的知识将用于改进早期破裂如何影响后续事件的时间和性质的应力模型。本研究包括对gps测量的变形、地震活动变化和其他地球物理数据的综合分析，以建立区域变形和应力瞬态的良好约束模型。该项目的主要目标是：(1)区分各种地震后变形过程的贡献；(2)量化整个地区的瞬态变形和应力的范围和分布，特别是来自上地幔的深层松弛；(3)确定影响整个地区活跃地震活动的时间依赖应力扰动的程度、量级和模式。在他们的建模中，研究人员依赖于球对称、可压缩、自重力地球上地震后松弛的解析粘弹性正态解和数值有限元技术。有限元技术考虑了俯冲板块边界带的横向非均质性和俯冲板块的作用。这项工作最重要的影响是通过提高地震情景和概率的准确性，为缅甸-安达曼-苏门答腊-爪哇板块边界带的地震危险性评估做出贡献。

The December 26, 2004 Sumatra-Andaman earthquake was the largest event since the 1960s and the first magnitude 9 earthquake to occur in the era of modern space geodesy and broadband seismology. This earthquake produced measurable static surface displacements at distances as large as 4500 km. Given the tremendous size of the 2004 earthquake, a ?second wave? of accelerated asthenospheric flow has developed that is going to perturb the regional deformation field for many decades. In addition, other postseismic deformation processes such as localized afterslip and poroelastic rebound, will also affect the regional deformation field. In fact, deformation measurements of the first few months following the Sumatra-Andaman earthquake can be explained quite well by either kinematic models of localized afterslip along and mostly below the rupture, or by viscoelastic relaxation. The 2004 earthquake was followed three months later by a great magnitude 8.7 event on an adjoining segment of the subduction zone, and again in 2007 by a magnitude 8.4 earthquake. This earthquake sequence provide the rare opportunity to fundamentally improve our understanding of the earthquake cycle of megathrust ruptures and the constitutive properties of the adjoining oceanic and continental crust and upper mantle. The knowledge the research team is gaining from this work will be applied towards improved stress models of how earlier ruptures influenced the timing and nature of subsequent events. This study includes a comprehensive analysis of GPS-measured deformation, seismicity changes and other geophysical data in order to develop well-constrained models of regional deformation and stress transients. The main goals of the project are to (1) differentiate the contributions from the various postseismic deformation processes, (2) to quantify the reach and distribution of transient deformation and stress across the region, especially from deep-seated relaxation in the upper mantle, and (3) to determine the extent, magnitude and pattern of time dependent stress perturbations affecting active seismicity throughout the region. In their modeling, the investigators rely on analytical viscoelastic normal mode solutions for post-earthquake relaxation on a spherically symmetric, compressible, self-gravitating Earth and on numerical finite element techniques. The finite element techniques allow for consideration of lateral heterogeneity across the subduction plate boundary zone and for the role of the subducting slab. The most important impact of this work is to contribute to earthquake hazard assessments for the Burma-Andaman-Sumatra-Java plate boundary zone by improving the accuracy of earthquake scenarios and probabilities.