An Investigation into Time-Dependent Fault Zone Properties at Seismogenic Depth on the San Andreas Fault near Parkfield

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。这个项目的目的是通过在孕震深度对随时间变化的断裂带属性提供更好的地震学约束来提高我们对地震成核过程的理解。加利福尼亚州帕克菲尔德密集的井下地震仪网络提供了大量高质量的地震数据，为揭示地下断裂带属性的详细信息提供了机会。我们试图开发新的方法来利用大量已识别的特征重复地震序列，并确定孕震深度的三个时变性质：1)断裂带强度，2)流变行为，3)内断裂带的滞弹性模型。该项目将探索重复地震序列震源性质的时间变化，作为断层强度变化的替代指标，以更好地了解随时间变化的断层强度在断层变形机制和地震成核过程中的作用。我们寻求显著扩展重复的地震活动数据，以大大提高圣安德烈亚斯断层沿线断层强度的时空分辨率。该项目的其他重点将包括了解深部空间和时间变化的流变性，以及成像2004年帕克菲尔德6级地震后地震后狭窄断层核心内的瞬时或系统结构变化。该项目将利用加利福尼亚州帕克菲尔德密集的井下地震仪网络积累的大量已确定的重复地震的优势，调查孕震深度的时变断裂带强度，这将影响地震的触发和排序。该项目的其他活动将探索断裂带流变性的时空变化，并将表征震后形变期断裂带中央核心的时间变化，以更全面地了解时变断裂带特性在地震成核过程中的作用。该项目将通过改进对地下随时间变化的断裂带属性的了解，直接改善对圣安德烈亚斯断层地震潜力的估计。该项目的成果将用于当地社区和组织减轻地震灾害的工作。该项目将包括一名研究生的教育和研究。

This award is funded under the American Recovery and Reinvestment Act of2009 (Public Law 111-5). This project aims to improve our understanding of the nucleation process of earthquakes by contributing better seismological constraints of time-dependent fault zone properties at seismogenic depth. The availability of a large number of high-quality seismic data from a dense borehole seismograph network at Parkfield, California introduces opportunities for unraveling detailed view of subsurface fault-zone properties. We seek to develop new approaches to take advantage of numerous identified sequences of characteristic repeating earthquakes, and to determine three time-dependent properties at seismogenic depth: 1) fault-zone strength, 2) rheological behaviors, and 3) anelastic model of the inner fault zone. The project will explore temporal variations in source properties of repeating earthquake sequence as a proxy for changes in fault strength to gain a better understanding of the role of time-dependent fault strength on the mechanics of fault deformation and the earthquake nucleation process. We seek to significantly expand repeating seismicity data to allow for much improved spatiotemporal resolution of fault strength along the San Andreas Fault. The other focuses of this project will involve understanding space- and time-varying rheological properties at depth and imaging transient or systematic structural changes within the narrow fault core in the postseismic period following the 2004 M6 Parkfield earthquake.This project will investigate time-varying fault-zone strength at seismogenic depth that will effect the triggering and sequencing of earthquakes, by taking the advantage of the numerous identified repeating earthquakes accumulating from a dense borehole seismograph network at Parkfield, California. The other activities of this project will explore spatiotemporal variations in fault-zone rheological properties and will characterize temporal changes in the central core of fault zone in postseismic deformation period, in order to gain a more comprehensive picture of the role of time-varying fault zone properties on the earthquake nucleation process. The project will directly contribute improved estimates of earthquake potential on the San Andreas Fault by improved knowledge of subsurface time-dependent fault zone properties. Results from the project will be used in earthquake hazard mitigation efforts by local communities and organizations. The project will include the education and research of a graduate student.