Collaborative Research: Deformation Processes in the Andaman Islands

合作研究：安达曼群岛的变形过程

• 批准号: 1114268
• 负责人: Anthony Lowry
• 金额: $ 11.13万
• 依托单位: Utah State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1114268&HistoricalAwards=false
• 关键词: Collaborative; Research; Deformation; Processes; Andaman

By capturing the postseismic deformation following the 2004 Sumatra-Andaman great earthquake, this project continues a six-year effort to understand the evolution of transient strain and stress. Several dozen studies have examined geodetic measurements of the transient deformation that followed the event, but the dominant mechanisms and processes involved in near-field deformation remain murky. Most of these studies conclude that a small amount of accelerated downdip slip occurred in the first few weeks or months following the earthquake, but that subsequent postseismic deformation and uplift are dominated by deeper viscoelastic flow. The most recent two years of near-field data from the Andaman region however exhibit uplift and right-lateral shear that is not replicated in existing models of viscoelastic flow. Expansion of the network would optimize the greater network to isolate nonlinear viscoelastic flow response by (1) extending the network coverage across the along-strike region of largest postseismic signal present in the time-variable geoid response, and (2) pairing up closely-spaced sites, enabling us to fingerprint fault slip signals superimposed on the desired flow signals.U Memphis collaborators will perform the maintenance and measurements at both continuous and campaign sites, in partnership with Center for Earth Sciences, Indian Institute of Science, Bangalore. All data will be archived at, and openly available from, the UNAVCO Facility which is also loaning several receivers for this project. Utah State University will combine these measurements with other local and regional GPS network data, and with GRACE time-variable gravity data, to model the full evolution of transient stress and strain in the region. We will refine existing estimates of the coseismic slip and examine (separately and together) models of fault slip, viscoelastic flow and poroelastic flow to determine which deformation processes are the most likely mechanisms for observed transients.The earthquake cycle is driven by a slow build-up of shallow stress within the earthquake zone. These shallow stress changes result from quiet slip on faults and flow of rocks at greater depths where temperatures are higher. Our understanding of the deeper fault slip and flow processes is limited by the difficulty of measuring small changes at great depths, but importantly these processes are briefly accelerated to measurable rates immediately following large earthquakes. The 2004 Sumatra-Andaman earthquake was the third-largest ever recorded, and GPS measurements indicate that it moved the ground surface in the Andaman and Nicobar Islands by up to sixteen feet toward India, and as much as three feet upward or downward. Since then, the islands have continued moving rapidly, totaling an additional foot toward India and a foot upward. Conventional scientific wisdom holds that the motion may be largely fault-slip driven in the first few weeks to months after an earthquake, but should be dominated by deeper flow in the years that follow. However, the most recent two years of measurements show anomalous motion that is not consistent with existing rock flow models, but would be consistent with predictions for fault slip. This project will combine GPS and gravity data with new modeling tools to try to understand this surprising observation, with special attention to how stress changes resulting from deep fault slip may influence the stress that drives deep rock flow, and vice-versa. The project?s scientific objectives have potentially far-reaching implications for our fundamental understanding of earthquake physics, seismic hazard, and the evolution of stress throughout the earthquake cycle.

通过捕捉2004年苏门答腊-安达曼大地震后的震后变形，该项目继续了六年的努力，以了解瞬态应变和应力的演变。几十项研究已经检查了事件发生后瞬时变形的大地测量结果，但近场变形所涉及的主要机制和过程仍然不清楚。大多数研究得出的结论是，少量的加速下倾滑动发生在地震后的头几个星期或几个月，但随后的震后变形和隆升是由更深的粘弹性流动。然而，安达曼地区最近两年的近场数据显示出隆起和右侧剪切，这在现有的粘弹流模型中无法复制。网络的扩展将优化更大的网络，以通过以下方式隔离非线性粘弹性流动响应：（1）将网络覆盖范围扩展到时变大地水准面响应中存在的最大震后信号的沿走向区域，以及（2）将紧密间隔的站点配对，使我们能够识别叠加在所需流量信号上的断层滑动信号。U孟菲斯合作者将在与班加罗尔印度科学研究所地球科学中心合作，在连续和运动地点开展活动。所有数据都将在联合国艾滋病毒/艾滋病联合规划署设施存档，并可从该设施公开查阅，该设施也为该项目借用了几个接收器。犹他州州立大学将联合收割机将这些测量结果与其他当地和区域GPS网络数据以及GRACE时变重力数据相结合，以模拟该地区瞬态应力和应变的全面演变。我们将完善现有的同震滑动的估计，并检查（单独和一起）断层滑动，粘弹性流动和多孔弹性流动的模型，以确定哪些变形过程是最有可能的机制，观察到的transients.The地震周期是由一个缓慢的建立浅应力在地震带内。这些浅层的应力变化是由于断层上的静滑动和温度较高的更深处的岩石流动造成的。我们对更深层次断层滑动和流动过程的理解受到在大深度测量微小变化的困难的限制，但重要的是，这些过程在大地震后立即被短暂加速到可测量的速率。2004年苏门答腊-安达曼地震是有记录以来第三大地震，GPS测量表明，它使安达曼和尼科巴群岛的地面向印度移动了16英尺，向上或向下移动了3英尺。从那时起，这些岛屿继续快速移动，总共向印度增加了一英尺，向上增加了一英尺。传统的科学观点认为，在地震发生后的最初几周到几个月内，这种运动可能主要是由断层滑动驱动的，但在随后的几年里，这种运动应该由更深层次的流动主导。然而，最近两年的测量结果显示，异常运动与现有的岩石流动模型不一致，但与断层滑动的预测一致。该项目将把联合收割机GPS和重力数据与新的建模工具结合起来，试图理解这一令人惊讶的观测结果，特别关注深层断层滑动造成的应力变化如何影响驱动深层岩石流动的应力，反之亦然。项目？的科学目标对我们对地震物理学、地震危险性和整个地震周期应力演化的基本理解具有潜在的深远影响。