Observations and models of postseismic deformation: Constraints on the ductile strength of continental lithosphere

震后变形的观测和模型：大陆岩石圈延性强度的约束

• 批准号: 0944336
• 负责人: Yuri Fialko
• 金额: $ 36.59万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-02-01 至 2014-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0944336&HistoricalAwards=false
• 关键词: Observations; models; postseismic; deformation; Constraints

Large shallow earthquakes generate sudden stress perturbations in the ambient rocks that may induce a ductile response of the lower crust and the uppermost mantle. Much improved global imaging of surface deformation due to the existing Synthetic Aperture Radar satellites (in particular, the L-band ALOS mission) allows us to measure the delayed postseismic response of the crust and upper mantle to the coseismically induced stress changes in areas of recent large earthquakes (most of which occurred in remote and poorly accessible regions). Measurements of postseismic transients bear on a long-standing debate on the effective rheology of the lithosphere below the brittle-ductile transition. Commonly considered models of postseismic transients include enhanced creep on a seismic rupture or its extension below the brittle-ductile transition (the so-called afterslip), poro-elastic rebound of the fluid-saturated crust, and visco-elastic relaxation of the lower crust or upper mantle. A robust discrimination (or some assessment of relative importance) of these mechanisms is often hindered by similarities in the predicted patterns of surface displacements. Such discrimination is nevertheless critical for our understanding of post-earthquake stress changes, delayed triggering of seismicity, and long-term strength of the ductile part of the continental lithosphere. We will use space geodetic observations and a new modeling approach based on elastic solutions for equivalent body forces in a spectral domain to study postseismic deformation due to three major recent earthquakes from diverse tectonic settings: the 2003 M7.2 Altai (Russia) earthquake, the 2006 M7.0 Mozambique earthquake, and the 2008 M7.9 Sichuan (China) earthquake. Data that will be used to constrain our models will primarily come from the ALOS mission of the Japanese Space Agency. The chosen events are characterized by different mechanisms (strike-slip, normal, and mixed thrust/strike-slip, respectively) which may greatly help with identifying a dominant relaxation mechanism and deducing the effective long-term strength of a ductile portion of the lithosphere in the corresponding locations.Detailed observations of post-seismic deformation in diverse tectonic settings will provide new constraints on the effective mechanical thickness and strength of the continental lithosphere. Such constraints will improve our understanding of continental tectonics. Physically-based models of post-seismic deformation might help forecast the evolution of stress and strain in the Earth crust following large earthquakes, and provide a useful input for seismic hazard estimates. Computer codes developed under the auspices of this project will be made available to a wider research community. Data and modeling results will be used in two graduate classes taught at SIO/UCSD.

大型浅源地震会在周围岩石中产生突然的应力扰动，可能引起下地壳和最上地幔的延性响应。 由于现有的合成孔径雷达卫星（特别是 L 波段 ALOS 任务），地表变形的全球成像得到了很大改善，使我们能够测量地壳和上地幔对最近地区同震引起的应力变化的延迟震后响应。大地震（大部分发生在偏远和交通不便的地区）。震后瞬变的测量与关于脆性转变以下岩石圈的有效流变学的长期争论有关。通常考虑的震后瞬变模型包括地震破裂的增强蠕变或其在脆性转变以下的延伸（所谓的后滑）、流体饱和地壳的孔隙弹性回弹以及下地壳的粘弹性松弛或上地幔。对这些机制的强有力的区分（或对相对重要性的一些评估）常常受到表面位移预测模式的相似性的阻碍。然而，这种区分对于我们理解震后应力变化、地震活动的延迟触发以及大陆岩石圈延性部分的长期强度至关重要。我们将使用空间大地测量观测和基于谱域中等效体力弹性解的新建模方法来研究最近发生的来自不同构造环境的三场重大地震造成的震后变形：2003 年 M7.2 阿尔泰（俄罗斯）地震、 2006年莫桑比克M7.0地震和2008年四川（中国）M7.9地震。用于约束我们模型的数据主要来自日本航天局的 ALOS 任务。所选事件具有不同的机制（分别为走滑、正向和混合推力/走滑），这可能极大地有助于识别主要松弛机制并推断岩石圈延性部分的有效长期强度对不同构造环境下震后变形的详细观测将为大陆岩石圈的有效机械厚度和强度提供新的约束。这些限制将增进我们对大陆构造的理解。基于物理的震后变形模型可能有助于预测大地震后地壳应力和应变的演变，并为地震灾害估计提供有用的输入。在该项目的支持下开发的计算机代码将提供给更广泛的研究界。数据和建模结果将用于 SIO/UCSD 教授的两个研究生课程。