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

大的浅层地震在周围岩石中产生突然的应力扰动，这可能会引起下地壳和最上地幔的韧性响应。由于现有的合成孔径雷达卫星(特别是L波段的ALOS任务)大大改善了地表形变的全球成像，使我们能够测量地壳和上地幔对近期大地震(大多数发生在偏远和难以接近的地区)同震诱发的应力变化的延迟震后响应。地震后瞬变的测量与关于脆性-韧性转变下岩石圈有效流变性的长期争论有关。通常认为的震后瞬变模型包括地震破裂上的强化蠕变或其在脆韧性转变(所谓的后滑)之下的延伸，流体饱和地壳的孔弹回弹，以及下地壳或上地幔的粘弹性松弛。对这些机制的有力区分(或对相对重要性的某种评估)往往受到地表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地震后应力变化、地震活动的延迟触发以及大陆岩石圈韧性部分的长期强度至关重要。我们将利用空间大地观测和基于谱域等效体力弹性解的新的建模方法来研究来自不同构造背景的三次近期大地震的震后变形：2003年俄罗斯阿拉泰7.2级地震、2006年莫桑比克7.0级地震和2008年中国7.9级地震。将用于约束我们的模型的数据将主要来自日本航天局的ALOS任务。所选择的事件具有不同的机制(分别为走滑、正常和混合的逆冲/走滑)，这将有助于确定主导的松弛机制，并推导出相应位置岩石圈韧性部分的有效长期强度。对不同构造背景下地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，并为地震危险性评估提供有用的信息。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在SIO/UCSD教授的两个研究生班。

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.