Collaborative Research: Integrating Observations of Low-Velocity Fault Zones with Models of Spontaneous Dynamic Earthquake Ruptures

合作研究：将低速断层带的观测与自发动力地震破裂模型相结合

• 批准号: 0809571
• 负责人: Benchun Duan
• 金额: $ 7.5万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-09-01 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0809571&HistoricalAwards=false
• 关键词: Collaborative; Research; Integrating; Observations; Low

Low-velocity fault zones (LVFZs) around many active faults with a reduction in seismic wave velocities of several to several tens percent relative to wall rocks have been detected by fault zone trapped waves and geodetic observations of the coseismic deformation. These LVFZs are mechanically distinct from the ambient crustal rock, as evidenced by their responses to nearby coseismic ruptures. A temporal reversal of the healing process of the 1992 Landers fault zone due to the nearby coseismic rupture of the 1999 Hector Mine earthquake and a net decrease in seismic velocities of at least 2.5% within the San Andreas fault zone due to the coseismic rupture of the 2004 M6 Parkfield earthquake have been documented. Displacements of several millimeters to several centimeters across several LVFZs due to nearby coseismic ruptures have also been observed by geodetic surveys. Earthquake source models used in previous studies to examine these observations of LVFZs are either dislocation (kinematic slip) models or point source models, which cannot accurately characterize the near-source dynamic stress and deformation fields. This project utilizes the most advanced spontaneous dynamic rupture model to investigate responses of LVFZs to nearby coseismic ruptures. Spontaneous dynamic rupture models build upon physical principles such as elasticity, elastoplasticity, and friction laws and provide physical insights to observations from real earthquakes. A finite element method (FEM) code for simulating spontaneous dynamic ruptures along geometrically complex faults and wave propagation in complex velocity structures has been verified in a community-wide code validation effort and is used in this study. Recent modifications to the FEM, including addition of elastoplastic off-fault response to dynamic ruptures, allow the PIs to more accurately calculate dynamic stress field and to better examine responses of LVFZs to coseismic ruptures. This project also investigates how a LVFZ surrounding a rupturing fault affects spontaneous dynamic rupture on the fault and near-field ground motion. With elastoplastic off-fault response included in spontaneous dynamic rupture models, the PIs examine interactions of inhomogeneous material distribution, off-fault damage and spontaneous dynamic rupture and effects on near-field ground motion. This project integrates observations of LVFZs with models of spontaneous dynamic ruptures. Compared with kinematic or point source models, spontaneous dynamic rupture models provide more accurate quantification of how LVFZs respond to earthquake coseismic ruptures, which has significant implications for improving our understanding of fault zone mechanics and stress and strain transfer in fault systems. Observations of LVFZs provide constraints to parameters in dynamic rupture models, including velocity structure of LVFZs and material strength (i.e., cohesion and internal friction). These observation-constrained model parameters can be used to support studies of other significant questions, such as prediction of strong ground motion at critical facility sites and in earthquake-prone areas. Results from this study are expected to promote the integration of observation and theory in earthquake sciences, and to impact both observation-oriented and theory-oriented communities of earthquake sciences.

在许多活动断层周围的低速断层区（LVFZ），相对于壁岩的地震波速度降低了几个百分之几以下的壁岩，并且被断层区捕获的波浪和cose震动变形的大地观察结果检测到。这些LVFZ在机械上与环境地壳岩石不同，这是它们对附近Coseis震动破裂的反应所证明的。由于1999年的1999年赫克托矿山地震破裂，1992年陆军断层造成的愈合过程的时间逆转和地震速度的净降低至少2.5％，这是由于2004年M6 Park菲尔德地震的cose震动而导致的。由于大地测量调查，还观察到，由于附近的Coseiscic破裂，还观察到了几毫米到几厘米的几厘米的位移。以前的研究中使用的地震源模型检查了LVFZ的这些观察结果是位错（运动学滑移）模型或点源模型，该模型无法准确表征近源动态应力和变形场。该项目利用最先进的自发动态破裂模型来研究LVFZ对附近Coseissic破裂的反应。自发动态破裂模型建立在诸如弹性，弹性性和摩擦定律等物理原理的基础上，并为来自真实地震的观察提供了物理见解。一种有限元方法（FEM）代码用于模拟复杂速度结构中的几何复杂断层和波传播沿着几何复杂的故障和波传播的代码，已在社区范围的代码验证工作中进行了验证，并在本研究中使用。最近对FEM的修改，包括增加对动态破裂的弹性塑料OFFORT响应，使PI可以更准确地计算动态应力场，并更好地检查LVFZ对Coseissic破裂的反应。该项目还研究了破裂断层周围的LVFZ如何影响断层和近场地面运动的自发动态破裂。随着自发动态破裂模型中包含弹性塑料的OFF响应，PIS检查了不均匀材料分布，OFF损坏和自发动态破裂以及对近场地面运动的影响的相互作用。该项目将LVFZ的观察结果与自发动态破裂模型相结合。与运动学或点源模型相比，自发动态破裂模型提供了更准确的量化LVFZ对地震抗震的反应，这对提高了我们对断层机械的理解以及断层系统中的压力和应变的理解具有重要意义。 LVFZ的观察结果对动态破裂模型中的参数提供了约束，包括LVFZ的速度结构和材料强度（即凝聚力和内部摩擦）。这些观察受限的模型参数可用于支持对其他重要问题的研究，例如在关键设施站点和地震易于地震的地区预测强大的地面运动。这项研究的结果预计将促进地震科学中观察和理论的整合，并影响地震科学的面向观察和以理论为导向的社区。