Rupture Propagation and Arrest in Geometrically Complex Fault Systems: Branches, Stepovers, and Damaged Border Zones

几何复杂断层系统中的破裂传播和停止：分支、跨步和损坏的边界区域

• 批准号: 0809610
• 负责人: James Rice
• 金额: $ 54万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0809610&HistoricalAwards=false
• 关键词: Rupture; Propagation; Arrest; Geometrically; Complex

The project group focuses on a major problem in earthquake science, namely, to understand the interaction of seismic slip-rupture with geometrical and structural complexities of fault zones. Such interactions include transitions of the failure path among fault strands at bends, branches and stepovers, rupture arrest, and induced inelastic deformations in fault border zones, which are generally damaged (highly cracked and/or granulated) and fluid-saturated. Prior work of the group, on which the current studies build, provided new understanding of how rupture paths are chosen at branch-like geometric complexities, and of how inelastic response of the fault bordering zone affects rupture propagation and shear localizations. The new areas for theory and modeling in current work are as follows: (1) Understanding how interactions of deformations with ground fluids and frictional elastic-plastic responses in the damage zone couple to the dynamics of rupture propagation. That includes explaining the effects of different types of across-fault material dissimilarity (in elastic properties, strength and extent of damage, and near-fault permeability to fluids); such dissimilarities are common for mature, highly slipped faults. (2) Assessing if, and to what extent, current understanding of how rupture paths are chosen at branch intersections, and of whether rupture passes through or arrests at step-overs, is affected by the presence of extensively damaged material, capable of elastic-plastic response, near such fault junctions. (3) Determining how residual stress states imprinted in fault-border material by the previous rupture affects response in the next event, and how that depends on rupture directivity in the past and pending events; (4) Devising procedures to rigorously analyze strain localizations that arise in modeling inelastic response of damaged/granulated fault border zones, by imposing localization-limiting procedures that eliminate grid dependence, thus ultimately evolving a methodology that can predict spontaneous development of localized fault-rupture paths through damaged material. Correlation of theory and modeling with field examples and lab experiments is a hallmark of the group's work, and new thrusts in that direction are as follows: (I) Adopting methodology like in (4) above to understanding when a damaged pull-apart stepover, like in the 1992 Landers earthquake between the Johnson and Homestead Valley Faults, and between the Homestead Valley and the Emerson Fault, is breeched by a through-going rupture, and similarly for the 1920 M8 Haiyuan, China event, which ruptured through a sequence of pull-aparts. (II) Understanding mega-branches of great thrust ruptures onto splay faults through the sediment cover of accretionary subduction zones, like documented or suspected at Alaska, Cascadia, Nankai and Sumatra, as well as when and by what processes branching onto landward- versus seaward-vergent splays can occur, and what that means for tsunami generation. (III) Testing the evolving theoretical understanding of rupture branching and interactions with damaged border zones against results of lab experiments (conducted by colleagues elsewhere) which are devised to address the same issues. The understanding of when and how earthquake ruptures stop, which often involves geometric complexities of the type we address, is central to understanding seismic risk. New ways of using relic fault geometries to constrain directivity and other features of past events is also a potentially valuable outcome.

该项目组专注于地震科学中的一个主要问题，即了解地震滑动破裂与断裂带几何和结构复杂性的相互作用。这种相互作用包括弯曲、分支和陡坡处断层链之间的失效路径转变，破裂阻止，以及在断层边缘地带诱导的非弹性变形，这些断层边缘地带通常是受损的(高度破裂和/或颗粒化)和流体饱和。该小组先前的工作为目前的研究提供了新的理解，即如何在树枝状的几何复杂情况下选择破裂路径，以及断层交界区的非弹性响应如何影响破裂传播和剪切局部化。目前理论和模拟的新领域如下：(1)了解破坏带内变形与地下流体的相互作用和摩擦弹塑性响应如何与破裂传播动力学相耦合。这包括解释不同类型的跨断层材料差异的影响(在弹性性质、破坏强度和程度以及近断层对流体的渗透性方面)；这种差异对于成熟的、高度滑动的断层来说是常见的。(2)评估目前对在分支交叉口如何选择破裂路径的理解，以及对断裂是否穿过或在跨越处发生堵塞的理解，是否受到此类断层交界处附近具有弹塑性反应能力的严重受损物质的影响。(3)确定上一次破裂压印在断层边缘材料上的残余应力状态如何影响下一次事件的响应，以及这如何取决于过去和即将发生的事件中的破裂方向性；(4)设计程序，通过实施消除网格依赖的局部化限制程序，严格分析在模拟受损/颗粒状断层边缘带的非弹性响应时出现的应变局部化，从而最终演变出一种能够预测局部断层破裂路径通过受损材料的自发发展的方法。理论和模拟与现场实例和实验室实验的相关性是该小组工作的一个特点，这方面的新进展如下：(I)采用如上(4)中所述的方法来了解破坏的拉分跨接带何时被贯穿破裂所阻碍，例如1992年约翰逊和霍姆斯特德山谷断层之间以及霍姆斯特德山谷和艾默生断层之间的兰德斯地震，1920年海原8级地震中国地震也是如此。(Ii)通过阿拉斯加、卡斯卡迪亚、南开和苏门答腊岛等增量俯冲带的沉积盖层，了解巨大逆冲断裂的巨型分支破裂到伸展断层上，以及何时和通过什么过程可以发生向陆地与向海洋的伸展，以及这对海啸的发生意味着什么。(3)对照实验室实验(由其他地方的同事进行)的结果，测试对破裂、分支和与受损边界地区相互作用的不断发展的理论理解，这些实验是为解决同样的问题而设计的。对地震破裂何时以及如何停止的理解，通常涉及我们所讨论的类型的几何复杂性，是理解地震风险的核心。利用遗留断层几何学来限制过去事件的方向性和其他特征的新方法也是一个潜在的有价值的结果。