Geodynamic Modeling of Long-term Fault Interactions During the Evolution of the Pacific-North American Plate Boundary Zone

圣安德烈亚斯断层是太平洋板块和北美板块之间的构造边界，然而只有一部分相对板块运动被圣安德烈亚斯断层本身的滑动所吸收。其余的，高达25%，是由一个复杂的断层系统容纳在一个广阔的板块边界带，由东加利福尼亚剪切带。这种板块边界带的弥散变形是造成加州和内华达州广泛分布地震的原因，但目前尚不清楚加州东部剪切带和圣安德烈亚斯断层系统中的其他断层是如何形成的，以及是什么控制了这些断层之间的应变分配。本研究项目将试图解决以下问题：1)是什么导致了东加利福尼亚剪切带的产生和发展？2)数百万年来东加利福尼亚剪切带、加洛克断层和圣哈辛托断层的发育如何影响圣安德烈亚斯断层板块边界带的地壳动力学？该研究采用长期力学耦合和断层相互作用的数值模拟，研究小组将开发三维区域尺度岩石圈变形的有限元模型。该模型中的粘弹塑性公式可以模拟断层外地壳的应变局部化，从而产生新的断层。板块边界是主要的断裂带，相对的板块运动产生集中的地壳变形、火山和地震。然而，太平洋-北美板块边界是一个主要的例外。在这里的板块边界，圣安德烈亚斯断层只吸收了部分相对板块运动，其余部分被许多断层的滑动所容纳，这是一个延伸到内华达州中部的复杂系统。提出的研究旨在了解为什么这些断层开始和什么控制这些断层之间的应变分配。这项研究的结果将帮助我们更好地理解观测到的地壳运动的地球动力学含义，从而为加利福尼亚和内华达州的地震提供见解。

The San Andreas Fault is the tectonic boundary between the Pacific and the North American plates, yet only a portion of the relative plate motion is absorbed by slip on the San Andreas Fault proper. The rest, up to 25 per cent, is accommodated by a complex system of faults over a broad plate boundary zone, by the Eastern California shear zone. Such diffuse deformation in the plate boundary zone is responsible for the widely scattered earthquakes in California and Nevada, but it is not clear how the Eastern California shear zone and other faults in the San Andreas Fault system formed, and what controls the strain partitioning among these faults. This research project will attempt to address the following questions: 1) what caused the inception and development of the Eastern California shear zone? 2) how has the development of the Eastern California shear zone, the Garlock Fault, and the San Jacinto Fault in the past few million years affected the crustal dynamics in the San Andreas Fault plate boundary zone? The study employs numerical modeling of long-term mechanical coupling and fault interactions in which the research team will develop a finite element model for three-dimensional, regional-scale lithospheric deformation. The viscoelastoplastic formulation in this model allows simulation of strain localization in the crust outside the faults, hence the inception of new faults.Plate boundaries are major fault zones, across which the relative plate motion produces concentrated crustal deformation, volcanoes, and earthquakes. However, the Pacific- North American plate boundary is a major exception. Here the plate boundary, the San Andreas fault absorbs only part of the relative plate motion and the rest is accommodated by slip on many faults in a complex system that extents into central Nevada. The proposed research seeks to understand why these fault initiated and what controls strain partitioning among these faults. The results of this study will help us to better understand the geodynamic implications of the observed crustal motion, hence provide insights into earthquakes in California and Nevada.