Interseismic and Postseismic Deformation and Stress Evolution: Effects of Rheology, Rupture History, and Fault System Geometry

知识价值：地球范围和相关活动将提供来自许多学科的关于地壳如何在大范围的空间和时间尺度上变形的大量数据。从潜在过程的角度解释来自不同来源的数据（例如，应力测量、大地测量、古地震学、结构地震学）需要模型——包括概念模型和数值模型。关于地质、大地测量和地震时间尺度上的变形如何相关的基于模型的推断需要对流变学、几何和地震作用力的描述。为了有用，模型必须简单到足以理解，同时仍然足够真实。模型预测参数化得越简单，模型就越有可能用于建立关于系统行为的直觉和理解。地球内部的岩石在响应与地震周期相关的应力和应力变化时，通过广泛的机制发生变形。大多数简单的地震后和地震间应变积累模型计算简单，应用广泛，指导了社区直觉的发展，但存在明显的局限性。这些问题包括：关于地壳流变行为的假设，与地球物理观察到的瞬变蠕变的重要性相矛盾；地壳中的背景应力通常比同震应力变化大一个数量级或更多的事实；地震几乎从不产生新的断层，但几乎总是在同一构造上发生许多以前的地震；而且地震几乎从来都不是周期性的，也很少破裂大到足以用二维粘弹性松弛模型中隐含的无限长断层破裂来充分近似的断层块。为了更好地理解地球的过程，以及利用Earthscope的高质量数据进行大地测量、古地震学、应力测量和地震学，至关重要的是要付出大量的努力来改进我们的模型。虽然最终需要大规模的计算工作，但在短期内（对仪器的定位、指导更复杂方法的发展和对现有数据的解释很重要），相对简单的模型- -有些是分析的，有些是数值的- -正在取得重大进展。目标是获得对更现实的流变假设的重要性的理解，提供有用的数值参数化，并使这种新的理解更容易被更广泛的社区使用，例如，作为Matlab代码，以及网络上的动画。更广泛的影响：正在开发工具来实现地壳和上地幔的流变描述，这在材料科学的基础上有了改进。这些工具使科学家能够在大范围的时间尺度上研究地壳变形。这项工作正在改进与地震周期相关的过程的基于模型的推断，从而改进地震风险的量化，更好地理解地震的物理性质，以及这些过程与与地壳长期动力学相关的过程之间的联系。这个项目为麻省理工学院的研究生提供了独特的教育体验，包括与科学和社会相关的令人兴奋的研究的本科生。

Intellectual Merit: Earthscope and associated activities are about to provide an avalanche of data from many disciplines about how Earth's crust deforms on a wide range of space and time scales. Interpreting data from diverse sources (e.g., stress measurements, geodesy, paleoseismology, structural seismology) in terms of the underlying processes requires models - both conceptual and numerical. Model-based inference of how deformation on geologic, geodetic, and seismic time scales are related requires descriptions of the rheology, geometry, and forcing by earthquakes. To be useful, a model must be simple enough to understand, while still being sufficiently realistic. The more simply model predictions can be parameterized, the more likely it is that the model will be used in building intuition and understanding about how the system behaves.Rocks in Earth's interior deform by a wide range of mechanisms in response to the stresses and stress changes associated with the seismic cycle. Most of the simple models of postseismic and interseismic strain-accumulation that are straightforward to calculate and in wide-spread use, guiding the development of intuition by the community, have significant limitations. These include assumptions about the rheological behavior of the crust that contradict geophysical observations of the importance of transient creep, the reality that the background stress in the crust is typically an order of magnitude or more greater than coseismic stress changes, that earthquakes almost never create new faults, but are almost always preceded by many previous earthquakes on the same structures, and that earthquakes are almost never periodic and rarely rupture fault patches large enough to be adequately approximated by the infinitely long fault ruptures implicit in 2D models of viscoelastic relaxation. In order to gain better understanding of earth processes, as well as to take advantage of the high quality data from Earthscope for geodesy, paleoseismoogy, stress measurements, and seismology, it is crucial that substantial effort be devoted to improving our models. While ultimately a large-scale computational effort will be needed, in the short term (important for siting of instruments, guiding development of more sophisticated approaches, and interpretation of existing data), significant progress is being made with relatively simple models - some analytic, some numerical. The goal is to obtain understanding of the importance of more realistic rheological assumptions, to provide useful numerical parameterizations and to make this new understanding easily useable by the broader community, e.g., as Matlab codes, and as animations on the web.Broader Implications: Tools are being developed that implement rheological descriptions of the crust and upper mantle that have an improved basis in materials science. These tools allow scientists to address crustal deformation over a broad range of time scales. This effort is improving model-based inference of the processes associated with the seismic cycle, leading to improved quantification of seismic risk, better understanding of the physics of earthquakes, and a link between these processes and processes associated with longer-term dynamics of the crust. This project provides unique educational experience for MIT graduate students and includes undergraduates in exciting research of relevance to both science and society.