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.

大的浅源地震在周围岩石中产生突然的应力扰动，这可能引起下地壳和上地幔的韧性响应。 由于现有的合成孔径雷达卫星（特别是L波段ALOS使命），地表变形的全球成像得到了很大改进，使我们能够测量地壳和上地幔对最近大地震地区（其中大多数发生在偏远和交通不便的地区）同震引起的应力变化的延迟震后反应。地震后瞬态的测量与脆-韧性转换层以下岩石圈的有效流变性的长期争论有关。通常考虑的震后瞬变模型包括地震破裂或其延伸到脆-韧性转换以下的增强蠕变（所谓的后滑），流体饱和地壳的孔隙弹性回弹，以及下地壳或上地幔的粘弹性松弛。一个强大的歧视（或相对重要性的一些评估），这些机制往往阻碍了相似的预测模式的表面位移。然而，这种歧视是至关重要的，我们了解地震后的应力变化，延迟触发地震活动，以及大陆岩石圈的韧性部分的长期强度。我们将使用空间大地测量观测和一种新的建模方法的基础上，弹性解决方案的等效体力在谱域研究震后变形由于三个主要的近期地震从不同的构造环境：2003年M7.2阿尔泰（俄罗斯）地震，2006年M7.0莫桑比克地震，和2008年M7.9四川（中国）地震。用于约束我们模型的数据将主要来自日本航天局的ALOS使命。所选事件的特点是不同的机制（走滑、正常和混合逆冲/走滑，这可能极大地有助于确定一种主导的松弛机制，并推导出相应位置岩石圈韧性部分的有效长期强度。不同构造背景下的地震变形将对大陆岩石圈的有效力学厚度和强度提供新的约束。这些限制将提高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，并为地震危险性估计提供有用的输入。在该项目主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。