Collaborative Research: Ten years later: Resolving the postseismic deformation processes of the 2002 Denali Fault earthquake

地球对大地震的反应并不会在地震震动消失时结束。大地震极大地改变了地球内部的力（应力），通过测量和模拟对这些变化的反应，我们可以了解深层断层带及其周围物质的力学特性。地球的这种随时间变化的瞬态响应会产生震后变形，我们将使用高精度GPS进行测量。震后变形研究的一个关键挑战是分离两个主要机制的影响，深断层面上的后滑或继续滑动，以及地幔和/或下地壳内的粘弹性松弛。在地震后的最初几年里，这两种机制可以在地球表面产生类似的变形，但它们随着时间的推移以不同的速度衰减。在本项目中，我们将使用2002年德纳里断层地震后的长时间数据记录（长达15年），以建立地震后变形的完整模型。这种改进的力学模型将使我们能够更好地了解驱动阿拉斯加构造变形的力量，以及地震之间的相互作用。我们将对2002年断层破裂周围的密集网络进行GPS调查。这些数据将提供重要的空间分辨率，以补充来自板块边界观测站的稀疏连续GPS网络，该网络提供有关震后变形时间演变的关键信息。我们将仔细检查观测到的变形，以确定可以完全或大部分由一个单一的震后机制解释的观测结果，如果可能的话，这使得它更容易约束模型参数。我们将重新计算一个新的同震滑移分布，使用有限元代码，可以利用完整的3-D推断的弹性地球结构，包括俯冲板，使我们能够最准确地计算地震后的响应滑动。我们将开发3D有限元模型和其他模型来解释观察到的变形，并评估这些模型将如何响应其他应力变化，如1964年地震或冰川卸载。我们将通过与德纳利国家公园的互动，与公众分享有关德纳利断层、阿拉斯加地震以及本项目成果的信息。公园每年接待约40万游客，与公园协调的外联工作提供了接触广泛受众的机会。

The Earth's response to large earthquakes does not end when the seismic shaking dies away. Large earthquakes substantially change forces (stresses) within the Earth, and by measuring and modeling the response to these changes, we can learn about the mechanical properties of deep fault zones and the material that surrounds them. This time-dependent and transient response of the Earth produces postseismic deformation, which we will measure using high-precision GPS. A key challenge of postseismic deformation studies is to separate the effects of the two main mechanisms, afterslip or continued slip on the deep fault plane, and viscoelastic relaxation within the mantle and/or lower crust. In the first few years after the earthquake, these two mechanisms can produce similar deformation at the surface of the Earth, but they decay with time at different rates. In this project, we will use a long record of data (up to 15 years) following the 2002 Denali fault earthquake to develop a complete model for the postseismic deformation following this earthquake. This improved mechanical model will allow us to better understand the forces that drive tectonic deformation in Alaska, and the interaction between earthquakes.We will carry out GPS surveys of a dense network of sites surrounding the 2002 fault rupture. These data will provide important spatial resolution to complement the sparse continuous GPS network from the Plate Boundary Observatory, which provides critical information about the time evolution of the postseismic deformation. We will carefully examine the observed deformation to identify observations that can be explained entirely or mostly by a single postseismic mechanism, if possible, which makes it easier to constrain model parameters. We will recalculate a new coseismic slip distribution using a finite element code that can utilize the full 3-D inferred elastic Earth structure, including the subducting slab, so that we can most accurately compute the postseismic response to the slip. We will develop 3D finite element models and other models to explain the observed deformation, and evaluate how these models would respond to other stress changes like the 1964 earthquake, or glacial unloading. We will share information about the Denali fault, earthquakes in Alaska, and the results of this project with the public through interaction with Denali National Park. The Park hosts about 400,000 visitors each year and coordinated outreach efforts with the Park offer a chance to reach a broad audience.