Collaborative research: Unraveling coseismic and postseismic deformation: A prerequisite for analyses of stress-coupling and tsunami genesis.

合作研究：揭示同震和震后变形：分析应力耦合和海啸成因的先决条件。

• 批准号: 1264288
• 负责人: Timothy Masterlark
• 金额: $ 13.12万
• 依托单位: South Dakota School of Mines and Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1264288&HistoricalAwards=false
• 关键词: Collaborative; research; Unraveling; coseismic; postseismic

The December 26, 2004 M9.2 Sumatra-Andaman Earthquake (SAE), the third largest earthquake ever recorded, ruptured the boundary separating the subducting Indo-Australian Plate from the overriding Burma Plate and triggered a devastating tsunami that significantly impacted 9 countries bordering the Indian Ocean. Near the epicenter, the tsunami caused over 30 meters of run-up in some coastal areas of Northern Sumatra, almost instantly killing over 200,000 people. The rupture of the SAE included more than 20 meters of fault-slip, based on associated seismologic data and GPS measurements of seafloor and ground deformation. This magnitude of deformation provides a rare opportunity to conduct a regional-scale in-situ rheological experiment, in which the coseismic fault-slip is the impulse and the subsequent deformation is the response. Modeling these measured perturbations can test hypotheses of coseismic (including tsunami-genesis) and postseismic (including earthquake-coupling and tsunami run-up) behavior. Specifically, Finite Element Models (FEMs) of the subduction zone near the epicenter allow for a quantitative evaluation of the role of rheologic partitioning and processes, on the stress, strain, and pore pressure that govern coseismic and postseismic behavior. Tsunami propagation models can then use FEM-generated seafloor deformations to predict coastal run-up. This modeling and interpretive study of the SAE will address the following scientific questions: (1) How does the distribution of material properties (i.e., structure, density, porosity, and stiffness of rock formations in the subduction zone) affect fault-slip estimations ? (2) How does this distribution influence seafloor deformation, tsunami genesis, and run-up predictions ? (3) What is the timing and distribution of poroelastic and viscoelastic postseismic deformation ? (4) What afterslip is required ? (5) Do Coulomb stress and pore pressure transients correlate to aftershock occurrence ? These questions are underpinned by a more fundamental question: How do we construct and constrain models of coseismic and postseismic behavior as a synthesis of processes, all of which contribute to the deformational system ? Accordingly, the primary goal of the proposed research is to determine the distribution and calibration of rheologic properties that describe coseismic and postseismic behavior of the SAE. More specifically, FEM simulations will address aftershock occurrence in both space and time (including stress-coupling between the SAE and the March 25, 2005 M8.7 Nias earthquake that occurred 350 km away from the SAE epicenter). FEM-generated seafloor deformation predictions will drive tsunami propagation simulations. Because we expect that variations in material properties (and possibly secondary splay faulting) will cause both long and shorter scale seafloor deformations, tsunami generation and propagation simulations will be performed with the dispersive long wave model FUNWAVE. Tsunami hazards will be expressed in terms of simulated run-up and inundation for the most affected areas of the Indian Ocean (e.g., Northern Sumatra), and compared to the observed impact of the 12/26/04 tsunami. This synoptic approach to simulating coseismic and postseismic deformational systems may significantly advance tectonic and tsunami coastal hazard assessment capabilities for the SAE and impact future assessments of similar mega-thrust earthquakes for other subduction zones hosting high population densities, such as the upper US West Coast (Cascadia) and Japan. Techniques for designing and implementing FEMs will be disseminated to the scientific community during a workshop in the latter stages of this project. Students will use Abaqus software to construct FEMs that simulate fault-slip, which can be used in forward and inverse models of deformation and drive of postseismic processes, including poroelastic and viscoelastic deformation.

2004年12月26日发生的M9.2苏门答腊-安达曼地震（SAE）是有记录以来的第三大地震，它使俯冲的印度-澳大利亚板块与上覆的缅甸板块之间的边界破裂，引发了毁灭性的海啸，严重影响了印度洋沿岸的9个国家。在震中附近，海啸导致苏门答腊岛北部一些沿海地区海平面上升超过 30 米，几乎立即造成超过 20 万人死亡。根据相关地震数据以及海底和地面变形的 GPS 测量，SAE 的破裂包括超过 20 米的断层滑动。这种变形幅度为进行区域尺度的原位流变实验提供了难得的机会，其中同震断层滑动是脉冲，随后的变形是响应。对这些测量到的扰动进行建模可以测试同震（包括海啸发生）和震后（包括地震耦合和海啸上升）行为的假设。具体来说，震中附近俯冲带的有限元模型 (FEM) 可以定量评估流变分区和过程对控制同震和震后行为的应力、应变和孔隙压力的作用。然后，海啸传播模型可以使用 FEM 生成的海底变形来预测海岸上升。 SAE 的建模和解释研究将解决以下科学问题：（1）材料特性的分布（即俯冲带岩层的结构、密度、孔隙度和刚度）如何影响断层滑动估计？ (2) 这种分布如何影响海底变形、海啸发生和上升预测？ (3) 孔隙弹性和粘弹性震后变形的时间和分布是怎样的？ (4) 需要什么后滑？ (5) 库仑应力和孔隙压力瞬变与余震发生相关吗？这些问题由一个更基本的问题支撑：我们如何构建和约束同震和震后行为的模型作为过程的综合，所有这些过程都对变形系统有贡献？因此，本研究的主要目标是确定描述 SAE 的同震和震后行为的流变特性的分布和校准。更具体地说，FEM 模拟将解决空间和时间上的余震发生问题（包括 SAE 与 2005 年 3 月 25 日发生在距 SAE 震中 350 公里处的 M8.7 尼亚斯地震之间的应力耦合）。有限元法生成的海底变形预测将推动海啸传播模拟。因为我们预计材料特性的变化（以及可能的二次张开断层）将导致长尺度和短尺度海底变形，因此海啸的产生和传播模拟将使用色散长波模型 FUNWAVE 进行。海啸危害将通过印度洋受影响最严重地区（例如苏门答腊岛北部）的模拟上升和淹没来表示，并与观测到的 2004 年 12 月 26 日海啸的影响进行比较。这种模拟同震和震后变形系统的天气方法可能会显着提高 SAE 的构造和海啸沿海灾害评估能力，并影响未来对其他人口密度较高的俯冲带（例如美国西海岸上游（卡斯卡迪亚）和日本）类似特大逆冲地震的评估。设计和实施有限元法的技术将在该项目后期的研讨会期间向科学界传播。学生将使用 Abaqus 软件构建模拟断层滑动的有限元模型，该模型可用于震后过程的变形和驱动的正向和逆向模型，包括多孔弹性和粘弹性变形。