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

当地震震动消失时，地球对大地震的反应并没有结束。大地震在很大程度上改变了地球内部的力(应力)，通过测量和模拟对这些变化的响应，我们可以了解深部断裂带的力学特性及其周围的物质。地球的这种随时间变化的瞬变响应会产生震后变形，我们将使用高精度的GPS进行测量。震后形变研究的一个关键挑战是分离深部断层面上的余滑或持续滑动以及地幔和/或下地壳内的粘弹性松弛这两种主要机制的影响。在地震后的头几年，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。在这个项目中，我们将使用2002年德纳利断层地震后的长达15年的数据记录来开发这次地震后震后变形的完整模型。这个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年断层破裂周围密集的地点网络进行GPS测量。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，该网络提供了有关震后形变的时间演变的关键信息。我们将仔细检查观测到的形变，以确定可以完全或主要由单一震后机制解释的观测结果，如果可能，这将使约束模型参数变得更容易。我们将使用有限元程序重新计算新的同震滑动分布，该有限元程序可以利用包括俯冲板在内的完整三维推断的弹性地球结构，以便我们可以最准确地计算地震后对滑动的响应。我们将开发3D有限元模型和其他模型来解释观测到的变形，并评估这些模型对1964年地震或冰川卸荷等其他应力变化的反应。我们将通过与德纳利国家公园的互动，与公众分享德纳利断层、阿拉斯加地震以及该项目的成果。公园每年接待约40万游客，与公园协调的外展工作提供了接触广泛观众的机会。

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.