Collaborative Research: Deformation Processes in the Andaman Islands

2004年12月的苏门答腊岛-安达曼地震是有记录以来第二大(MW9.3)和第二致命(约28万人伤亡)的地震。它的不同寻常之处还在于它结合了正常的、快速的？伴随着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来研究两个可能对全球地震研究具有广泛影响的问题：(1)在岛弧背景下发生大地震后，什么过程和流变学使应力重新平衡？以及(2)在大地震中，是什么地球特性控制着破裂的速度？印度板块和安达曼构造板块之间的边界几乎完全是海底的，但安达曼-尼科巴岛群能够揭示地震后该部分的变形，该部分主要作为一次缓慢的地震破裂，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-尼科巴群岛运营一个由14个全球定位系统(GPS)站点组成的网络，继续捕捉苏门答腊-安达曼地震后的震后形变。该网络目前由4个连续不断和10个竞选地点组成。这些？事实真相？大地测量数据(来自一个数据获取困难的地方出了名)正与重力和海岸线变化的卫星测量相结合，以研究有关俯冲推覆的变形和应力循环的关键科学问题。在过去一个世纪最大的地震之一中，俯冲推覆显示出异常的慢滑行为。对头几年GPS震后位移的模拟表明，在此期间，地震破裂以近场变形为主的滑移向下倾斜。模拟表明，早期的断层滑动响应现在已经完成，地幔流动将在未来几年主导近场变形。该网络的设计目的是捕捉这些粘弹性流动信号，识别任何可能揭示浅板边界推覆滑动稳定性的连续断层滑动，并评估幂函数蠕变流变学的时间和空间相关的非线性效应是否明显。尤其是通过检查数据来评估滑动稳定性，以寻找非线性断层滑动(所谓的？慢滑事件？)的证据。在地震中破裂的浅板块边界上。人们还在研究岩石流动过程，以寻找一种不同类型的非线性的证据，这种证据预计是基于实验室的岩石变形实验，但在真实的地球上并没有明确观察到。孟菲斯大学的研究人员正在与班加罗尔的印度科学研究所和安达曼与尼科巴生态学会(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立大学(USU)的研究人员的专业知识。大地震后重新平衡应力的变形过程本质上与导致大地震的应力积累过程有关，因此这项正在进行的研究将阐明地震滑动的物理学和全球地震周期

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