Dynamically Self-Consistent Contstraints on the Long-Term Strength of Faults in Western North America

这项工作促进了对北美西部板块边界带内断层、下地壳和上地幔长期强度的认识。对活动断层稳定滑动的长期摩擦阻力的约束包含了影响地震破裂和地震周期的过程的信息，例如动态弱化机制、孔隙压力的作用以及断层测量等内在弱点的作用。利用第四纪断层数据库和GPS速度作为约束，对北美西部的观测约束运动学和动力学模型进行了改进。GPS数据的长波分量被用来帮助约束长期变形场，而瞬态信号被过滤掉。此外，第四纪断层数据库中的无长度变化方向，以及断层样式和滑动矢量方向，正被用来帮助约束北美西部最新第四纪的长期变形场。对应变速率的主轴方向和主轴相对大小（断层类型）的长期估计提供了导致这种变形的偏应力场的方向和类型的代理。动力学模型受到地形、重力、地震定义的地壳厚度和密度、热流以及对全球地幔环流模型重要的观测结果（如层析成像和俯冲史）的限制。在这些动力学模型的基础上，断层长期摩擦行为约束的研究取得了重大进展，因为(1)在脆性地壳和岩石圈内作用的垂直综合偏应力的绝对量级被量化；(2)采用了一种通用的方法来解释在板块边界带观察到的断层机制的巨大变化。此外，假设正在使用一般的三维模型进行测试，该模型适当地处理横向强度各向异性，强度剖面特征的横向变化以及由表面地形和莫霍面引起的不均匀层厚。这笔拨款将用于支持石溪大学研究生艾略特·克莱因的博士研究。这项工作将为指导参与北美西部板块边界带可视化工具开发的REU本科生提供进一步的支持。这些可视化工具将在联安援助团的互动网站（http://jules.unavco.org/）上展示。此外，这项研究还进一步支持了更新ILP全球应变率图（GSRM）互动网站上现有模型的活动，该网站用于教学和研究（www.world-strain-map.org）。此外，这项工作还为扩大和丰富研究生丹尼尔·埃尔南德斯（Daniel Hernandez）的活动提供了基础设施支持，他来自一个代表性不足的群体。建议的工作是基础研究。它将推进有关断层长期强度的基本知识，并对断层力学甚至地震破裂能量收支和地震周期具有重要意义。然而，我们为年轻一代所做的贡献本身就具有社会效益。

This work is advancing the understanding of the long-term strength of faults, lower crust, and upper mantle within the plate boundary zone of Western North America. Constraints on the long-term frictional resistance to steady sliding on active faults holds information on processes that affect earthquake rupture and the seismic cycle in general, such as dynamic weakening mechanisms, the role of pore pressure, and the role of intrinsic weakness, such as fault gauge. Observationally constrained kinematic and dynamic models of western North America are being refined using the Quaternary Fault database and GPS velocities as a constraint. The long-wavelength components of the GPS data are being used to help constrain the long-term deformation field, while the transient signal is filtered out. Moreover, the no-length-change directions in the Quaternary Fault database, along with fault style and slip vector directions, are being used to help constrain the long-term deformation field for latest Quaternary in western North America. The long-term estimates of the directions of principal axes and relative magnitudes of principal axes (style of faulting) for the rates of strain provide a proxy for orientation and style of deviatoric stress field responsible for such deformation. Dynamic models are constrained by topography, gravity, seismically defined crustal thicknesses and densities, heat flow, as well as the observations important for global mantle circulation models, such as tomography and history of subduction. Given these dynamic models, significant advances are being made on the constraints of long-term frictional behavior of faults because (1) the absolute magnitudes of vertically integrated deviatoric stresses acting within the brittle crust and the lithosphere are quantified and (2) a general approach is applied that accounts for the dramatic change in fault mechanisms observed across the plate boundary zone. Furthermore, hypotheses are being tested using a general three-dimensional model that properly deals with lateral strength anisotropy, lateral variations in strength profile characteristics, and non-uniform layer thicknesses resulting from topography on the surface and the Moho. The grant will be used to support the Ph.D. research of Stony Brook graduate student Elliot Klein. This work is providing further support for the mentoring of REU undergraduates who participate in development of visualization tools for understanding the plate boundary zone in western North America. These visualization tools will be displayed on the interactive web site maintained at UNAVCO (http://jules.unavco.org/). Moreover, this research is further supporting activities to updateexisting models on the ILP's Global Strain Rate Map (GSRM) interactive web site, used for both teaching and research (www.world-strain-map.org). In addition, this work is providing infrastructural support for broadening and enriching the activities of a graduate student, Daniel Hernandez, from an underrepresented group. The proposed work is basic research. It willadvance fundamental knowledge about the long-term strength of faults, and it holds implications for fault mechanics and even the earthquake rupture energy budget and earthquake cycle. However, the contributions we make to the younger generation are of societal benefit in itself.