Collaborative Research: Deformation Processes in the Andaman-Nicobar Islands

2004年12月的苏门答腊-安达曼地震是有记录以来第二大（Mw9.3）和第二致命（约280，000人伤亡）的地震。它也是不寻常的，因为它结合了正常？快吗？更不寻常的缓慢断层滑动事件的破裂。这一独特的事件提供了一个重要的机会，研究两个问题，潜在的广泛的影响，全球地震研究：（1）什么过程和流变学重新平衡应力后，大地震在岛弧设置？（2）地球的什么性质控制着大地震的破裂速度？印度板块和安达曼板块之间的边界几乎完全是海底的，但安达曼-尼科巴岛群使我们能够揭示这一部分的震后变形，这一部分主要是作为一个缓慢的地震破裂，因此产生的地面震动相对较小。该项目的调查人员通过在安达曼-尼科巴群岛上运行一个由14个全球定位系统站点组成的网络，继续捕捉苏门答腊-安达曼地震后的震后变形情况。该网络目前由4个连续的和10个运动网站组成。这些吗？地面实况大地测量数据（来自一个数据获取极为困难的地点）正与卫星重力和海岸线变化测量相结合，以研究有关俯冲逆冲断层变形和应力周期的关键科学问题，该逆冲断层在上世纪最大的地震之一期间表现出不寻常的缓慢滑动行为。GPS震后位移的前几年的建模表明，在此期间，地震破裂的滑动下倾主导近场变形。模拟表明，早期的断层滑动响应现在已经完成，地幔流将在未来几年内主导近场变形。该网络的目的是捕捉这些粘弹性流信号，指纹任何持续的断层滑动，可以照亮滑动稳定性的浅板块边界的推力，并评估是否时间和空间依赖的非线性效应的幂律蠕变流变学的证据。滑动稳定性，特别是正在评估通过检查数据的证据，非线性断层滑动（所谓的？慢滑事件？）在地震中破裂的浅板块边界上岩石流动过程也正在被研究，以寻找一种不同类型的非线性的证据，这种非线性是基于实验室岩石变形实验所预期的，但在真实的地球上还没有明确观察到。孟菲斯大学的研究人员正在与印度科学研究所、班加罗尔和安达曼尼科巴生态学会（SANE）合作运营GPS网络。建模和解释结合了孟菲斯大学和犹他州州立大学（USU）研究人员的专业知识。大地震后应力重新平衡的变形过程与导致大地震的应力积累过程有着内在的联系，因此，这项正在进行的研究将阐明全球地震滑动和地震周期的物理学

The December 2004 Sumatra-Andaman earthquake was the second largest (Mw 9.3) and second deadliest (~280,000 casualties) earthquake ever recorded. It was also unusual in that it combined a normal ?fast? rupture with a more unusual slow fault slip event. This unique occurrence presents an important opportunity to examine two questions with potentially wide-ranging implications for global earthquake studies: (1) What processes and rheologies re-equilibrate stress following great earthquakes in island arc settings? And (2) What Earth properties control the speed of rupture in great earthquakes? The boundary between the Indian and Andaman tectonic plates is almost entirely submarine, but the Andaman-Nicobar Island group enables a revealing look at postseismic deformation in the segment that ruptured principally as a slow earthquake and hence generated relatively little ground shaking. The investigators on this project are continuing to capture postseismic deformation after the Sumatra-Andaman earthquake by operating a network of 14 Global Positioning System (GPS) sites in the Andaman-Nicobar Islands. The network currently consists of 4 continuous and 10 campaign sites. These ?ground-truth? geodetic data (from a locale where data acquisition is notoriously difficult) are being combined with satellite measurements of gravity and shoreline changes to examine key scientific questions about the deformation and stress cycle on a subduction thrust that exhibited unusual slow slip behavior during one of the largest earthquakes of the past century. Modeling of the first several years of GPS postseismic displacements indicates slip down-dip of the seismic rupture dominated near-field deformation during that period. Modeling suggests the early fault slip response is now completed and that mantle flow will dominate near-field deformation for the next several years. The network is designed to capture these viscoelastic flow signals, to fingerprint any continuing fault slip that may illuminate slip stability of the shallow plate-bounding thrust, and to assess whether time- and space-dependent nonlinear effects of power-law creep rheology are in evidence. Slip stability in particular is being assessed by examining the data for evidence of nonlinear fault slip (so-called ?slow slip events?) on the shallow plate boundary that ruptured during the earthquake. The rock flow process is also being examined for evidence of a different type of nonlinearity that is expected based on laboratory rock deformation experiments, but that has not been observed unequivocally in the real Earth. University of Memphis investigators are operating the GPS network in partnership with the Indian Institute of Science, Bangalore and the Society of Andaman & Nicobar Ecology (SANE). Modeling and interpretation combines the expertise of investigators at the University of Memphis and Utah State University (USU). Deformation processes that re-equilibrate stress following large earthquakes are intrinsically linked to the processes that accumulate stress leading up to large earthquakes, so this ongoing investigation will illuminate the physics of earthquake slip and the earthquake cycle globally