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

学术价值：地球望远镜和相关活动即将提供来自许多学科的大量数据，这些数据关于地壳如何在广泛的空间和时间尺度上变形。根据基本过程解释来自不同来源(如应力测量、大地测量、古地震学、构造地震学)的数据需要概念模型和数值模型。基于模型的推断在地质、大地测量和地震时间尺度上的变形是如何相关的，需要对流变学、几何学和地震的强迫进行描述。要想有用，一个模型必须足够简单易懂，同时又足够现实。模型预测的参数越简单，模型就越有可能被用来建立直觉和理解系统的行为。地球内部的岩石通过一系列机制变形，以响应与地震周期相关的应力和应力变化。大多数简单的震后和震间应变累积模型都有很大的局限性，这些模型直接计算并被广泛使用，指导着社区对直觉的发展。这些假设包括关于地壳流变行为的假设，这些假设与地球物理观察中关于瞬时蠕变重要性的假设相矛盾，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大，地震几乎不会产生新的断层，但几乎总是在同一结构上的许多先前地震之前，以及地震几乎从来不是周期性的，很少破裂断层块足够大，足以用粘弹性松弛二维模型中隐含的无限长断层破裂来充分近似。为了更好地了解地球过程，以及利用来自地球望远镜的高质量数据用于大地测量、古地震学、应力测量和地震学，至关重要的是要投入大量努力来改进我们的模型。虽然最终将需要大规模的计算工作，但在短期内(对于仪器选址、指导更复杂方法的开发以及对现有数据的解释来说很重要)，相对简单的模型正在取得重大进展--一些是分析的，一些是数值的。其目标是了解更现实的流变学假设的重要性，提供有用的数值参数，并使这种新的理解易于被更广泛的社区使用，例如作为MatLab代码，以及作为网络上的动画。广泛的影响：正在开发工具，实现对地壳和上地幔的流变学描述，这些工具在材料科学方面有更好的基础。这些工具使科学家能够在广泛的时间范围内处理地壳形变问题。这项工作正在改进对与地震周期有关的过程的基于模型的推断，从而改进了对地震风险的量化，更好地了解了地震的物理学，并将这些过程和与地壳长期动力学有关的过程联系起来。这个项目为麻省理工学院的研究生提供了独特的教育经验，并包括本科生从事与科学和社会相关的令人兴奋的研究。

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.