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复杂性，可能发生在一个收敛的设置，包括斜俯冲和微板块碰撞，和上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有着丰富的GPS观测资料，因此是研究俯冲带地球动力学的主要地区。 然而，由于地震后的瞬态过程，从大地测量的约束中揭示应变的划分和应力的演变是复杂的。 该项目正在开发一个三维粘弹性有限元模型，可以预测对每个过程的反应，从而分离和阐明阿拉斯加岩石圈对震间负荷和震后瞬变的反应。 分析特别侧重于了解如何收敛之间的巨型逆冲断层和上板块断层系统的划分，以便能够计算如何通过地震周期的应力演变。 正在开发的模型涵盖了整个阿拉斯加中部和南部以及周边地区的上地幔底部，以确定板块运动和相关的地幔流（包括板块边缘引起的地幔流）如何影响上板块的应力和应变率。 断层明确模拟地震推断滑动分布，粘弹性过程利用幂律流变。 计算最终应允许跟踪地震周期中的速度、应变和应力率，包括过去世纪中由于震间加载和所有大地震以及相关的震后松弛而引起的应力演化，以及过去3000年中大俯冲带事件的周期。 该模型的另一个版本与解锁断层，根据摩擦和区域负载滑动将使长期（平均超过许多地震周期）的速度结构和应变积累的计算。 受地质滑动速率的限制，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增生杂岩。计算当代应力演化将导致识别目前以最大速率加载的区域和断层，在过去的世纪中具有最高的未释放应力负荷。 这些地区代表了地震风险最高的地区，自1964年上一次俯冲带大地震以来，人口已显着增长。 这些与时间相关的计算将能够生成动画，显示应变如何在地震周期中积累和应力如何波动，这是一种教育工具，将被纳入高中和本科阶段的课程计划。

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.