Fault Slip and Seismicity in Geometrically Complex Fault Systems

几何复杂断层系统中的断层滑动和地震活动

• 批准号: 0636064
• 负责人: James Dieterich
• 金额: $ 33万
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-01-15 至 2010-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0636064&HistoricalAwards=false
• 关键词: Fault; Slip; Seismicity; Geometrically; Complex

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.

该项目正在研究控制几何复杂断层上的滑动和地震发生的过程。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会发生的相互作用和过程。其中包括滑动、正应力和断层强度（由摩擦系数和正应力设置）之间的耦合相互作用。此外，为了适应几何不相容性，屈服和应力松弛过程必须伴随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，屈服主要是通过次生断层的发育来实现的。断层系统和断层粗糙度的分形特征表明，所有尺度的次生断层的轻微运动对于适应主要贯通断层的滑动是必要的。屈服表现为地震期间的同震断层变形、余震和弥散背景地震活动。该项目的建模组件采用边界元法的 2D 和 3D 实现来表示主要贯通断层之间的应力相互作用。主要断层的屈服和应力松弛是通过次断层上滑动的显式表示来建模的，并使用地震速率公式作为体积松弛来建模，该公式是从与速率和状态相关的断层本构特性导出的。使用该公式提供了一种表示地震活动性、屈服和应力松弛的方法，同时结合了时间和应力依赖性，这与断层滑移和地震现象（例如余震和前震）的实验室观察结果一致。该研究的观察部分使用各种数据集来测试理论结果并指导模型开发。这些包括背景地震活动和余震的生产力随距主要断层距离的特征衰减、余震和背景地震之间断层外地震活动的划分，以及震源机制解所指示的应力异质性和应力旋转。这项工作可能对地震的发生以及地震危险性分析产生影响。该项目还将支持一名有前途的博士后研究员。