Bimaterial Interfaces, Damage Zones, Earthquake Directivities and Signatures of Rupture Opening in the Parkfield Section of the San Andreas Fault

圣安德烈亚斯断层 Parkfield 段的双材料界面、损伤区、地震方向和破裂口特征

• 批准号: 0844103
• 负责人: Yehuda Ben-Zion
• 金额: $ 19.28万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0844103&HistoricalAwards=false
• 关键词: Bimaterial; Interfaces; Damage; Zones; Earthquake

The studies focus on systematic high-resolution imaging of bimaterial interfaces, low velocity fault zone layers, rupture directivities of earthquakes, and seismic signatures of opening rupture mode along various fault segments of the San Andreas Fault system in the Parkfield area. The overall goal is to provide multi-signal tests, based on large seismic waveform and catalog data sets, for the hypothesis that earthquakes on large strike-slip faults have preferred propagation directions that are controlled by the velocity contrasts across the faults, and for the possibility that earthquake ruptures on such faults have tensile component of faulting. The imaging of bimaterial interfaces employ fault zone head waves that refract along bimaterial faults and direct P waves. The fault zone head waves provide the most diagnostic signal for the existence of sharp bimaterial interfaces and the highest-resolution tool for imaging their seismic properties at depth. Fault zone trapped waves are used to quantify symmetry properties with respect to the main rupture surface and other characteristics of damaged fault zone layers at different locations. The analysis of rupture directivities involves stacking aftershock rates at the opposite along-strike directions of each event and observing symmetry properties of dynamic triggering patterns of the stacked data at different space-time scales. The examination for opening rupture mode utilizes several potential seismic signals that are suggested by recent theoretical calculations. The studies also focus on clarifying the structural and earthquake properties around the SAFOD site, clarifying properties of the main SAF between the hypocenters of the 1966 and 2004 M6 events, and clarifying the connectivity between the main SAF and the Southwest Fracture zone at depth. The studies can have profound implications for key aspects of earthquake and fault mechanics including effective constitutive laws, earthquake source and rupture properties, generated frictional heat, interaction between faults and more. The analyses can help resolving existing controversies. Positive results on statistical preference of earthquake propagation directions may lead to refined estimates of seismic shaking hazard near major faults.

这些研究集中在帕克菲尔德地区圣安德烈亚斯断裂系统不同断裂段的双物质界面、低速断层带层、地震破裂方向性和张开破裂模式的地震特征的系统高分辨率成像。总体目标是基于大型地震波形和目录数据集提供多信号测试，以验证大型走滑断层上的地震具有受断层上的速度对比控制的优先传播方向的假设，以及此类断层上的地震破裂具有断层拉伸成分的可能性。双材料界面的成像采用沿双材料断层折射的断裂带头波和直接的P波。断裂带头部波为尖锐的双物质界面的存在提供了最具诊断性的信号，也是在深部成像其地震性质的最高分辨率工具。利用断裂带俘获波对主破裂面的对称性和不同位置受损断裂带层的其他特征进行了量化。破裂方向性的分析包括在每个事件沿走向方向相反的方向上叠加余震率，并观察叠加数据在不同时空尺度上动态触发模式的对称性。对张开破裂模式的检验利用了最近的理论计算提出的几个潜在的地震信号。这些研究还侧重于澄清SAFOD场地周围的构造和地震性质，澄清1966和2004年6级地震震中之间的主要SAF的性质，以及澄清主要SAF与西南深部断裂带之间的连通性。这些研究可以对地震和断层力学的关键方面产生深远的影响，包括有效的本构关系、震源和破裂性质、产生的摩擦热、断层之间的相互作用等。这些分析有助于解决现有的争议。地震传播方向统计偏好性的积极结果可能导致对主要断层附近地震震动危险性的精确估计。