Non-volcanic Tremor in the Northern San Andreas Fault System

该项目旨在对圣安德烈亚斯断层系统内的非火山震动（一种最近发现的地震现象）与地震之间的关系提供更清晰的理解。沿着圣安德烈亚斯断层，人们只在加州帕克菲尔德附近的几个地方研究过地震，时间也很有限。这有效地将震颤的关联限制在一次更大的地震——2004年帕克菲尔德6级地震。我们观察到导致这次地震的地震速率和迁移模式的显著变化，然而，这一单一的例子不足以将前兆地震作为导致更大事件的一般现象。这个项目将大大扩展地震观测的地理和时间基础，并将允许更多的地震和大地震之间的联系进行研究。该项目包括对这些关联的详细分析，目的是建立对震颤和地震之间关系的更有力的理解。该项目还将在圣安德烈亚斯断层系统中寻找更多种类断层上的震颤，并对其进行特征描述，这将为地震提供额外的约束条件。变换系统?地震与俯冲带地震的比较。这个项目吗?对地震的特殊性质（即更深的深度，对小应力变化的敏感性，与变形率的相关性，与深层断层流体和来自潮汐和遥远大地震的应力的关联）的分析也将通过提供有关地震的成因、地震与深部断裂的关系、地球结构、深部地球性质和活动构造过程的信息，影响其他研究领域。该项目包括大量的学生参与（包括研究生和本科生），这将支持他们在科学和技术方面的培训和研究经验，并通过与女性早期职业地球物理学家Aurelie Guilhem （CEA/DAM/DIF，法国）和早期职业地球物理学家张海江教授（中国科技大学）的合作，增加与国际机构的伙伴关系以及早期职业和代表性不足群体的参与。加利福尼亚北部环境地震事件的探测主要依赖于加利福尼亚帕克菲尔德当地尺度高分辨率地震台网（HRSN）连续地震观测的敏感钻孔记录。这导致了加利福尼亚断层地震的狭隘观点。为了准确地描述加州地震的过程，准确地比较转换断层和俯冲带的地震，更清楚地了解地震与大地震的关系，需要在更广泛的断层系统上对地震进行更多的观察，并与更多的大地震相联系。该项目的目的是扩大地震观测的地理和时间范围，并从地震的角度分析扩大的数据集。与大量断层系统的关系及其结构、过程、推断成分和应力随时间变化。这项工作将通过全面和系统地搜索北加州大部分地区的环境和触发性地震来完成，这些地震可以追溯到20世纪90年代中期，主要使用美国地质勘探局北加州地震台网（NCSN）最近可用的连续地震记录数据集。该地区其他网络的连续记录也将进行分析。将采用包络相互关和百分位叠加的方法来解决地面NCSN台站灵敏度较低的问题。在可能的情况下，还将使用波形叠加和模式匹配扫描技术开发相应的高分辨率LFE目录。将采用已证实的方法来推断震源断裂带的力学和过程，并使用震源和台站对双差分方法进行速度和衰减层析成像，以改进地震位置并加强对深部断层性质和结构的理解。

This project seeks to provide a clearer understanding of the relationship between non-volcanic tremor (a recently discovered seismic phenomenon) and earthquakes within the San Andreas Fault System. Along the San Andreas Fault, tremor has been studied in only a few locations near Parkfield, California and for a limited time period. This has effectively limited the association of tremor to only one larger earthquake--the 2004 Parkfield magnitude 6 event. Notable changes in the rate and migration pattern of tremor leading up to this earthquake were observed, however, this single example is insufficient for establishing precursory tremor as a general phenomena leading up to larger events. This project will significantly expand the geographic and temporal base of tremor observations and will allow for a greater number of associations between tremor and larger earthquakes to be studied. Included in the project are detailed analyses of these associations with the aim of establishing a more robust understanding of the relationship between tremor and earthquakes. The project will also search for and characterize tremor on a greater diversity of faults within the San Andreas fault system, which will provide additional constraints on ?transform system? tremor for comparisons with subduction zone tremor. The project?s analyses of the special properties of tremor (i.e., greater depths, sensitivity to small stress change, correlation with deformation rates, and associations with deep fault fluids and stressing from earth-tides and distant large earthquakes) will also impact other fields of study by providing information on the genesis of tremor, the relationship of tremor with deep faulting, on earth-structure, deep earth properties, and on active tectonic processes. The project includes significant student participation (both graduate and undergraduate) that will support their training and research experience in science and technology, and it increases partnerships with international institutions and participation of early-career and underrepresented groups through collaboration with female early-career geophysicist Aurelie Guilhem (CEA/DAM/DIF, France) and early-career professor Haijiang Zhang (University of Science and Technology, China). Detections of ambient tremor events in northern California have relied primarily on sensitive borehole recordings of continuous seismic observations from the local-scale High Resolution Seismic Network (HRSN) at Parkfield, CA. This has resulted in a parochial view of tremor on California faults. Additional observations of tremor on a broader array of fault-systems and in association with a greater number of larger earthquakes are needed to accurately characterize the process of tremor in California, to accurately compare transform fault and subduction zone tremor, and to more clearly understand the relationship of tremor to larger earthquakes. The objective of this project is to expand the geographic and temporal scope of tremor observation and to analyze the expanded dataset in terms of tremors? relationships to a greater number of fault systems and their structures, process, inferred composition, and stress-change through time. This will be done through a comprehensive and systematic search for ambient and triggered tremor throughout much of northern California going back to the mid-1990s using, primarily, a recently available dataset of continuous seismic records from the regional USGS Northern California Seismic Network (NCSN). Continuous records from other networks in the region will also be analyzed. Envelope cross-correlation and percentile stacking methods will be used to deal with the lower sensitivity of the surface NCSN stations. Corresponding high-resolution LFE catalogs will also be developed when possible using waveform stacking and pattern match scanning techniques. Proven methods for inferring mechanics and process in the tremor-genic fault zones will be employed, and velocity and attenuation tomography using tremor sources and station-pair double-differencing methods will be performed to improve tremor locations and to enhance understanding of deep fault properties and structure.