Non-volcanic Tremor in the Northern San Andreas Fault System

北圣安德烈亚斯断层系的非火山震颤

• 批准号: 1460498
• 负责人: Robert Nadeau
• 金额: $ 43.21万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-07-01 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1460498&HistoricalAwards=false
• 关键词: Non; volcanic; Tremor; Northern; San

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.

该项目旨在更清楚地了解圣安德烈亚斯断层系统内的非火山震颤（最近发现的地震现象）和地震之间的关系。 沿着圣安德烈亚斯断层，只有在加州帕克菲尔德附近的几个地点和有限的时间内研究了震颤。 这有效地限制了震颤的关联，只有一个更大的地震-2004年帕克菲尔德6级事件。 观察到导致这次地震的震颤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地震作为导致更大事件的一般现象。该项目将大大扩展震颤观测的地理和时间基础，并将允许研究震颤与更大地震之间的更多关联。 该项目包括对这些关联的详细分析，目的是对震颤和地震之间的关系建立更可靠的理解。该项目还将搜索和表征震颤的更大的多样性断层内的圣安德烈亚斯断层系统，这将提供额外的限制？转换系统？与俯冲带震颤进行比较。项目？对震颤的特殊性质的分析（即，更大的深度，对小的应力变化的敏感性，与变形速率的相关性，以及与深部断层流体和来自地球潮汐和远距离大地震的应力的关联）也将通过提供关于震颤的成因、震颤与深部断层的关系、地球结构、深部地球性质和活动构造过程的信息而影响其他研究领域。 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发展学家Aurelie Guilhem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（CEA/DAM/DIF，法国）和张海江教授（中国科技大学）。北方加州的环境震颤事件的检测主要依赖于来自加利福尼亚州帕克菲尔德的局部尺度高分辨率地震网络（HRSN）的连续地震观测的灵敏钻孔记录。这导致了对加州断层的狭隘看法。为了准确描述加州的地震过程，准确地比较转换断层和俯冲带的地震，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更多的大地震进行额外的地震观测。该项目的目标是扩大地震观测的地理和时间范围，并根据地震分析扩大的数据集？与大量断层系统及其结构、过程、推断成分和应力随时间变化的关系。 这将通过全面和系统的搜索环境和触发震颤整个北方加利福尼亚州大部分地区追溯到20世纪90年代中期，主要使用最近可用的数据集的连续地震记录从区域USGS北方加州地震网络（NCSN）。还将分析该区域其他网络的连续记录。对于地面NCSN台站灵敏度较低的情况，将采用包络互相关和百分位叠加方法进行处理。在可能的情况下，还将利用波形叠加和模式匹配扫描技术编制相应的高分辨率LFE目录。将采用反演方法推断地震断层带的力学和过程，并将利用震源和站对双差方法进行速度和衰减层析成像，以改善地震定位，并加强对深部断层性质和结构的了解。