Non-volcanic Tremor in the Northern San Andreas Fault System

该项目旨在更清楚地了解非火山震动(最近发现的一种地震现象)与圣安德烈亚斯断层系统内地震之间的关系。沿着圣安德烈亚斯断层，只在加利福尼亚州帕克菲尔德附近的几个地点进行了有限的时间内的地震研究。这有效地将震颤与只有一次更大的地震联系在一起--2004年帕克菲尔德6级地震。在这次地震前，震动率和迁移模式发生了显著的变化，然而，这一单一的例子不足以确定前兆地震是导致更大地震的一般现象。该项目将极大地扩大地震观测的地理和时间基础，并将使更多的人能够研究地震和更大地震之间的联系。该项目包括对这些联系的详细分析，目的是更有力地了解震动和地震之间的关系。该项目还将在圣安德烈亚斯断层系统内更多样化的断层上寻找和表征地震，这将为转换系统提供额外的约束。用于与俯冲带地震进行比较的地震。S项目对地震的特殊性质(即更深的深度、对小应力变化的敏感性、与变形速率的相关性、与深部断层流体的联系以及来自固体潮和遥远的大地震的应力)的分析也将影响其他研究领域，提供关于地震的成因、地震与深断裂的关系、地球结构、深部地球性质和活动构造过程的信息。该项目包括大量的学生参与(研究生和本科生)，这将支持他们在科学技术方面的培训和研究经验，并通过与早期职业地球物理学家Aurelie Guilem(法国地球物理学家协会/DAM/DIF)和早期职业教授张海江(科技大学，中国)合作，增加与国际机构的伙伴关系，以及职业早期和代表性不足的群体的参与。对加利福尼亚州北部环境震动事件的探测主要依赖于加利福尼亚州帕克菲尔德的当地规模高分辨率地震台网(HRSN)连续地震观测的敏感钻孔记录。这导致了对加州断层地震的狭隘看法。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地震，以及更清楚地了解地震与更大地震的关系，需要对更广泛的断层系统和与更多较大地震有关的地震进行更多的观测。该项目的目标是扩大地震观测的地理和时间范围，并根据地震分析扩展的数据集。与更多的断层系统及其结构、过程、推断的组成和应力随时间变化的关系。这将通过全面和系统地搜索自20世纪90年代中期以来整个加州北部大部分地区的环境地震和触发地震来完成，主要使用最近从美国地质勘探局北加州地震台网(NCSN)获得的连续地震记录的数据集。还将分析来自该区域其他网络的连续记录。针对地面NCSN站灵敏度较低的问题，将采用包络互相关和百分位数叠加的方法。如果可能，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星表。将采用成熟的方法推断震源断裂带的力学和过程，并将使用震源和台对双差分方法进行速度和衰减层析成像，以改善地震位置并加强对深部断层性质和结构的了解。

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.