Collaborative Research: Multi-scale validation of earthquake source parameters to resolve any spatial, temporal or magnitude-dependent variability at Parkfield, CA

合作研究：对加利福尼亚州帕克菲尔德的地震源参数进行多尺度验证，以解决任何空间、时间或震级相关的变化

• 批准号: 1547071
• 负责人: Xiaowei Chen
• 金额: $ 22.43万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-15 至 2021-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1547071&HistoricalAwards=false
• 关键词: Collaborative; Research; Multi; scale; validation

Improved estimates of seismic hazard are necessary to reduce the major human and financial losses suffered in earthquakes every year. The stress released during an earthquake (called the stress drop) controls the ground accelerations produced by the earthquake waves, and hence the damage potential. The stress drop is also fundamental to understanding and modeling the physics of the earthquake source, because it defines the energy budget. It is important to know whether stress drop varies from region to region, and with earthquake magnitude. This is because earthquake parameters and ground shaking measurements in regions of high seismicity are often used to estimate hazard in other regions that may have lower historic seismicity rate, for example regions with induced seismicity. However it is currently unknown how much stress drop really varies between earthquakes. The observed variability ranges over a factor of 100 to 1000, which poses significant challenges in interpreting stress drop results. It is often not clear how much of the variability comes from measurement uncertainties, and how much represents real regional variations in fault properties. The investigators will focus on the section of the San Andreas Fault near Parkfield, in central California, where there is a high rate of earthquakes, including distinct sequences of small repeating earthquakes, and the fault also creeps slowly. It is one of the best-instrumented sections of fault in the world. The award will aid the development of a new geophysics group at the University of Oklahoma by supporting a beginning-career female PI, and a graduate student. The student will have the opportunity to be an active participant in the research communities in both Boston and Oklahoma. The research activities will help to establish earthquake research in Oklahoma, a state with increased awareness of earthquake hazard due to dramatic increase in seismicity, and will be integrated into classroom activities.The large number of earthquakes and the long-term dense networks of seismometers make this region a natural laboratory for understanding earthquake source physics. The multiple-scale dense observational networks provide on-scale recordings for a wide magnitude range; the existing detailed research provides a well-defined context in which to interpret the results. The Investigators propose to apply multi-scale (both large- and small-scale) analysis methods to the dense dataset of earthquake waveforms aimed at resolving the continuing controversy regarding earthquake scaling and variability. The investigators will calculate the stress release for a large number of earthquakes in multiple ways, using different subsets of the data. The work will focus on three distinct questions: (1) Is the apparent scaling of stress drop an artifact of poor data with limited bandwidth, limited magnitude range, and inadequate correction for site and propagation effects? (2) Do the stress drops of repeating earthquakes at Parkfield change with time as a result of the change in strain rate from the 2004 M6 Parkfield earthquake? (3) What data quality and analysis requirements are needed to confirm that spatial and temporal variations observed here and in future studies are real? The proposed research will increase understanding of the earthquake source process, both at Parkfield, and beyond. The methods developed, and the greater understanding of their limitations and constraints should enable a higher resolution of earthquake source parameters, and hence seismic hazard maps, worldwide.

为了减少每年地震造成的重大人员和经济损失，必须改进对地震灾害的估计。地震期间释放的应力（称为应力降）控制地震波产生的地面加速度，从而控制潜在的损坏。应力降也是理解和模拟震源物理的基础，因为它定义了能量预算。重要的是要了解应力降是否因地区而异以及地震震级是否不同。这是因为高地震活动区域的地震参数和地面震动测量通常用于估计历史地震活动率较低的其他区域（例如诱发地震活动的区域）的危险。然而，目前尚不清楚地震之间的应力降到底有多大差异。观察到的变异性范围超过 100 到 1000，这对解释压力下降结果提出了重大挑战。通常不清楚有多少变化来自测量不确定性，有多少代表断层属性的真实区域变化。研究人员将重点关注加利福尼亚州中部帕克菲尔德附近的圣安德烈亚斯断层部分，该地区地震发生率很高，包括明显的小规模重复地震序列，而且断层蠕动也很缓慢。它是世界上仪器仪表最齐全的断层区域之一。该奖项将通过支持一名刚开始职业生涯的女性 PI 和一名研究生，帮助俄克拉荷马大学新的地球物理学小组的发展。学生将有机会成为波士顿和俄克拉荷马州研究社区的积极参与者。研究活动将有助于在俄克拉荷马州建立地震研究，该州由于地震活动急剧增加，对地震危害的认识有所提高，并将融入课堂活动。大量的地震和长期密集的地震仪网络使得该地区是了解地震源物理的天然实验室。多尺度密集观测网络提供宽震级范围的按比例记录；现有的详细研究为解释结果提供了明确的背景。研究人员建议对地震波形的密集数据集应用多尺度（大尺度和小尺度）分析方法，旨在解决有关地震尺度和变异性的持续争议。研究人员将使用不同的数据子集以多种方式计算大量地震的应力释放。这项工作将集中于三个不同的问题：（1）应力降的明显缩放是否是带宽有限、幅度范围有限以及对站点和传播效应校正不充分的不良数据造成的？ (2) Parkfield 重复地震的应力降是否会因 2004 年 M6 Parkfield 地震应变率的变化而随时间变化？ (3) 需要哪些数据质量和分析要求来确认此处和未来研究中观察到的时空变化是真实的？拟议的研究将增加对帕克菲尔德及其他地区地震震源过程的了解。所开发的方法以及对其局限性和约束的更好理解应该能够实现更高分辨率的震源参数，从而获得全球范围内的地震灾害图。