Contemporary Strain and Stressing Rates in Central and Southern Alaska Through the Earthquake Cycle

阿拉斯加中部和南部表现出许多在会聚环境中可能发生的复杂性，包括倾斜俯冲和微板块碰撞，上部板块经历了广泛的构造反应，包括大型山脉、深盆地、长走滑断层系统和大俯冲带地震。阿拉斯加中部和南部拥有丰富的GPS观测资料，因此是研究俯冲带地球动力学的首选地区。然而，从大地测量约束中揭示应变的分配和应力的演变，由于持续的瞬态地震后过程而变得复杂。该项目致力于通过开发三维粘弹性有限元模型来隔离和阐明阿拉斯加岩石圈对地震间载荷和地震后瞬变的响应，该模型可以预测每个过程的响应。分析的重点是了解大逆冲断层和上板块断层系统之间的汇聚是如何划分的，以便能够计算出应力在地震周期中的演变情况。正在开发的模型包括阿拉斯加中部和南部以及上地幔底部的周边地区，以确定板块运动和相关的地幔流（包括由板块边缘引起的地幔流）如何影响上板块的应力和应变率。断层用推断的滑动分布来模拟地震，粘弹性过程利用幂律流变学。计算最终应允许通过地震周期跟踪速度、应变和应力率，包括过去一个世纪以来由于地震间载荷和所有大地震以及相关的震后松弛引起的应力演变，以及过去3000年的大俯冲带事件周期。该模型的另一种版本是，未解锁的断层根据摩擦和区域载荷滑动，将能够计算长期（在许多地震周期中平均）的速度结构和应变积累。受地质滑动率的限制，该模型将有助于深入了解阿拉斯加中部和南部广泛的构造特征的发展，从阿拉斯加中部山脉到从科迪亚克延伸到基奈半岛和楚加奇山脉的吸积complex。计算应力的当代演变将导致识别当前以最大速率加载的区域和断层，并且在过去的一个世纪中具有最高的未解除应力载荷。自1964年上一次俯冲带大地震以来，这些地区对人口来说是地震风险最高的地区。这些与时间相关的计算将能够生成动画，显示应力如何在地震周期中累积和波动，这是一种教育工具，将被纳入高中和本科水平的课程计划中。

Central and southern Alaska exhibit many of the complexities that can occur in a convergent setting, including oblique subduction and microplate collision, and the upper plate experiences a broad range of tectonic responses, including large mountain ranges, deep basins, long strike-slip fault systems, and great subduction zone earthquakes. With a wealth of GPS observations, central and southern Alaska is thus a premier area for studying the geodynamics of subduction zones. Unraveling the partitioning of strain and the evolution of stress from geodetic constraints is, however, complicated by on-going transient postseismic processes. This project is working to isolate and illuminate the response of the Alaskan lithosphere to interseismic loading and postseismic transients by developing a 3-D viscoelastic finite element model that can predict the response to each processes. The analysis is particularly focused on understanding of how convergence is partitioned between the megathrust and upper plate fault systems, so as to enable a calculation of how stress evolves through the earthquake cycle. The model being developed encompasses all of central and southern Alaska and the surrounding region to the base of upper mantle to determine how slab motion and associated mantle currents (included those induced by slab edges) influence stress and strain rates in the upper plate. Faults are modeled explicitly with earthquakes simulated by inferred slip distributions, and viscoelastic processes utilize power-law rheologies. Calculations should eventually allow for the tracking of velocity, strain, and stressing rates through the earthquake cycle, including the evolution of stress due to interseismic loading and all major earthquakes and associated postseismic relaxation over the past century, as well as a cycle of great subduction zone events over the past 3 millennia. An alternate version of the model with unlocked faults that slip in accordance with friction and regional loading will enable calculations of long-term (averaged over many earthquake cycles) velocity structure and strain accumulation. Constrained by geological slip rates, this model will lend insight into the development of the broad tectonic features exhibited in central and southern Alaska, from the Central Alaska Range to the accretionary complex that stretches from Kodiak to the Kenai Peninsula and the Chugach Mountains.Calculation of the contemporary evolution of stress will lead to the identification of regions and faults that are currently being loaded at the greatest rate and have the highest unrelieved stress loads over the past century. Such regions represent areas of highest seismic risk to a population that has grown significantly since the last great subduction zone quake in 1964. These time-dependent calculations will enable the generation of animations that show how strain accumulates and stress fluctuates through the earthquake cycle, an educational tool that will be incorporated into lesson plans at both the high school and undergraduate level.