Fault Slip and Seismicity in Geometrically Complex Fault Systems

这个项目是研究控制滑动和地震发生的过程在几何上复杂的断层。非平面断层和断层网络的滑动涉及标准平面断层模型中不存在的相互作用和过程。这些包括滑动、正应力和断层强度（由摩擦系数和正应力设定）之间的耦合相互作用。此外，为了适应几何不相容，屈服和应力松弛过程必须伴随着主要贯穿断层的滑动，以防止病理应力条件的发展（或在极端情况下断层锁定）。在脆性发震地壳中，屈服主要是通过次级断裂的发育来完成的。断裂系统的分形特征和断层的粗糙度表明，次级断层在各个尺度上的轻微运动都是适应主要贯穿断层滑动的必要条件。这种屈服表现为地震时的同震离断层变形、余震和弥散背景地震活动性。本项目建模部分采用边界元法的二维和三维实现来表示主要贯穿断层之间的应力相互作用。主要断层的屈服和应力松弛通过次级断层的滑动的显式表示来建模，并使用地震速率公式作为体松弛，该公式来源于速率和状态相关的断层本构性质。该公式的使用提供了一种表示地震活动性、屈服和应力松弛的方法，同时结合了与断层滑动和地震现象（如余震和前震）的实验室观测相一致的时间和应力依赖性。该研究的观测部分使用各种数据集来检验理论结果并指导模型开发。这些特征包括：与主要断层的距离对背景地震活动性和余震活动性的特征衰减，余震和背景地震之间断层外地震活动性的划分，以及震源机制解所表明的应力非均质性和应力旋转。这项工作可能会对地震的发生和地震危害分析产生影响。该项目还将支持一名有前途的博士后。

This project is investigating processes that control slip and earthquake occurrence on geometrically complex faults. Slip of non-planar faults and fault networks involves interactions and processes that do not occur in standard planar fault models. These include coupled interactions among slip, normal stress, and fault strength (as set by the coefficient of friction and normal stress). In addition, to accommodate geometric incompatibilities, yielding and stress relaxation processes must accompany slip of major through-going faults to prevent the development of pathological stress conditions (or in extreme cases fault lock-up). In the brittle seismogenic crust, yielding is accomplished principally through the development of secondary faults. The fractal-like character of fault systems and fault roughness indicates that slight movements of secondary faults at all scales are necessary to accommodate slip of major through-going faults. The yielding is manifest as coseismic off-fault deformation during earthquakes, as aftershocks, and as diffuse background seismicity. The modeling component of this project employs 2D and 3D implementations of the boundary element method to represent stress interactions among major through-going faults. Yielding and stress relaxation off of the major faults are modeled through explicit representations of slip on secondary faults, and as bulk relaxation using an earthquake rate formulation, which is derived from rate- and state-dependent fault constitutive properties. Use of this formulation affords a way to represent seismicity, yielding, and stress relaxation while incorporating time- and stress-dependencies that are consistent with laboratory observations of fault slip and earthquake phenomena, such as aftershocks and foreshocks. The observational component of the study uses a variety of data sets to test the theoretical results and guide model development. These include characteristic decay of the productivity of background seismicity and aftershocks by distance from major faults, partitioning of off-fault seismicity between aftershocks and background earthquakes, and stress heterogeneity and stress rotations as indicated by focal mechanism solutions. This work could have implications for the occurrence of earthquake and thus seismic hazard analysis. The project will also support a promising postdoctoral fellow.