COLLABORATIVE RESEARCH: Eathquake rupture dynamics on non-planar faults with off-fault damage

合作研究：具有断层损伤的非平面断层的地震破裂动力学

• 批准号: 0944066
• 负责人: Yehuda Ben-Zion
• 金额: $ 20.35万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0944066&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Eathquake; rupture; dynamics

Earthquakes generate dynamic stress concentrations near their rupture front and near geometrical irregularities that can exceed the strength of the surrounding material and produce inelastic brittle deformation in the bulk. Co-seismic off-fault failure induces both irreversible deformation (plasticity) and reduction of elastic moduli (damage) with potentially distinct signatures on the radiated wavefield and fault zone structure. Dynamic damage can amplify near-fault motions and produce bimaterial interfaces that affect the subsequent behavior of rupture. These feedback mechanisms between off-fault damage and dynamic rupture are not accounted for in models that represent off-fault dissipation by plastic yielding with unchanged elastic moduli. Moreover, natural faults contain geometrical features (roughness) over a broad range of length scales. The multiscale non-planar geometry of faults can enhance the complexity of dynamic rupture and high frequency wave radiation. Fault roughness also induces stress concentrations that can contribute to the generation of dynamic off-fault damage and affect the overall earthquake energy balance. The overarching goal of this project is to provide, through theoretical and computational modeling, quantitative predictions of the impact of off-fault brittle damage and fault roughness (and their feedback) on observable properties of earthquake rupture, seismic wave radiation and short-term evolution of fault zone structure. The research addresses directly the following fundamental questions about earthquake physics and fault dynamics: What are the intensity and spatial extent of the coseismic reduction of wave velocities around the earthquake source? How do off-fault inelasticity and fault roughness contribute to the apparent scaling of earthquake fracture energy? What are the limits imposed by damage on maximum slip rate and peak ground velocity? Can the across-fault asymmetry of dynamic damage induce significant bimaterial effects on rupture? Can dynamic brittle damage produce stronger wave radiation and generate observable non-double-couple seismic radiation? How does fault roughness affect the complexity of earthquake rupture, the distribution of damage and the properties of high frequency radiation? How is the macroscopic response of a fault related to the coupled mesoscopic properties of damage and roughness? Current studies of earthquake dynamics by several groups are pushing the frontier beyond the classical model of frictional sliding on a planar fault in elastic media to understand the role of a more realistic and complete set of ingredients. The diversity and complexity of the physical processes involved calls for a step-by-step approach in which a few candidate ingredients are tested at a time. The proposed studies aim to investigate the combined effects on dynamic ruptures and seismic radiation of two fundamental ingredients: non-planar fault geometry (fault roughness on a broad range of scales) and off-fault material damage (reduction of elastic moduli). Other related studies consider at present only large scale, kilometric features of fault geometry, and represent off-fault inelasticity by an ideal plastic rheology. The current project will consider fault geometry over a broad range of scales, from meters to kilometers, and will include co-seismic reduction of elastic moduli in the off-fault yielding process. The results can have transformative impact on studies of properties of dynamic ruptures, limits to the maximum expected ground motion, and inversions of observed seismic data for earthquake source properties. The research may provide new target signals for constraining earthquakes processes and dynamic evolution of fault zone structure. An improved understanding of properties of dynamic ruptures, high frequency seismic radiation and physical limits to ground motion will contribute to emerging physics-based approaches for earthquake engineering and mitigation of seismic hazard. The incorporation of material damage in the source process can have significant impact on many geophysical studies that are based on derived earthquake source parameters (e.g., fault slip and source mechanisms). The results will help to scale fault properties and processes from the laboratory to natural fault zones. Although our focus is on earthquake dynamics, the studies can also have impact on the solid mechanics and material science communities.

地震在其破裂前缘附近和几何不规则性附近产生动态应力集中，这些动态应力集中可能超过周围材料的强度，并在本体中产生非弹性脆性变形。同震断层外故障引起不可逆变形（塑性）和弹性模量（损伤）的降低，辐射波场和断层带结构上可能有不同的签名。动态损伤可以放大近断层运动，并产生影响断裂后续行为的双材料界面。这些反馈机制之间的故障损坏和动态断裂不占模型，代表故障耗散塑性屈服不变的弹性模量。此外，天然断层包含的几何特征（粗糙度）的长度尺度范围很广。断层的多尺度非平面几何形态可以增强动态破裂和高频波辐射的复杂性。断层粗糙度也会引起应力集中，这会导致动态断层外破坏的产生，并影响整体地震能量平衡。该项目的总体目标是通过理论和计算建模，定量预测断层外脆性损伤和断层粗糙度（及其反馈）对地震破裂、地震波辐射和断层带结构短期演化的可观察性质的影响。该研究直接解决了以下关于地震物理学和断层动力学的基本问题：震源周围波速同震降低的强度和空间范围是什么？断层外非弹性和断层粗糙度如何影响地震破裂能的表观尺度？损伤对最大滑移率和峰值地面速度的限制是什么？动力损伤的跨断层不对称性是否会引起显著的双材料断裂效应？动力脆性损伤能否产生更强的波辐射，产生可观测的非双力偶地震辐射？断层粗糙度如何影响地震破裂的复杂性、破坏分布和高频辐射特性？断层的宏观响应与损伤和粗糙度的耦合介观性质有何关系？目前，几个小组对地震动力学的研究正在推动边界超越弹性介质中平面断层上摩擦滑动的经典模型，以了解更现实和完整的一组成分的作用。所涉及的物理过程的多样性和复杂性要求采取一种逐步的方法，即一次测试几种候选成分。拟议的研究旨在调查的动态断裂和地震辐射的两个基本成分的综合影响：非平面断层几何形状（故障粗糙度的范围广泛的尺度）和断层外的材料损坏（弹性模量的减少）。其他相关的研究认为，目前只有大规模的，千米级的断层几何特征，并代表了理想的塑性流变断层非弹性。目前的项目将考虑从米到公里的大范围尺度上的断层几何形状，并将包括在断层外屈服过程中弹性模量的同震降低。结果可以有变革性的影响，研究动态断裂的属性，限制最大预期地面运动，和反演观测到的地震数据的震源属性。这一研究可为地震过程和断裂带结构的动态演化提供新的目标信号。对动态破裂、高频地震辐射和地面运动物理极限特性的更好理解将有助于地震工程和减轻地震灾害的新兴物理方法。在震源过程中纳入材料损伤可能对许多基于导出的震源参数（例如，断层滑动和震源机制）。这些结果将有助于将断层的性质和过程从实验室扩展到自然断层带。虽然我们的重点是地震动力学，但这些研究也会对固体力学和材料科学界产生影响。