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.

需要改善地震危害的估计值，以减少每年地震中的主要人类和财务损失。地震期间释放的应力（称为应力下降）控制着地震波产生的地面加速度，因此损害潜力。压力下降也是理解和建模地震来源的物理学的基础，因为它定义了能源预算。重要的是要知道应力下降是否因区域而异，并且随地震幅度而变化。这是因为在高地震性地区的地震参数和地面震动测量通常用于估计其他可能具有较低历史地震速率的地区的危害，例如具有诱发地震性的区域。但是，目前尚不清楚地震之间的压力下降到底有多少变化。观察到的变异性在100至1000倍以上，这在解释压力下降结果方面构成了重大挑战。通常不清楚多少可变性来自测量不确定性，以及多少代表故障属性的实际区域变化。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区，那里的地震发生率很高，包括不同的小重复地震序列，并且断层也缓慢蔓延。它是世界上最好的错误部分之一。该奖项将通过支持初学者Pi的PI和一名研究生来帮助俄克拉荷马大学的新地球物理小组的发展。该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，该州由于地震性的急剧增加而对地震危害的认识提高，并将整合到课堂活动中。大量的地震和长期密集的地震网络使该地区成为自然实验室，使自然实验室成为理解地震源物理学的自然实验室。多尺度密集的观测网络为广泛范围提供了尺寸的记录。现有的详细研究提供了一个定义明确的环境，可以在其中解释结果。研究人员建议将多尺度（大小和小规模）分析方法应用于地震波形的密集数据集，以解决有关地震缩放和可变性的持续争议。研究人员将使用数据的不同子集来以多种方式计算大量地震的应力释放。这项工作将重点放在三个不同的问题上：（1）应力的明显缩放是否会降低较差的数据的伪像，带宽有限，幅度范围有限，并且对位点和传播效应的校正不足？ （2）由于2004 M6 Parkfield地震的应变率变化而导致帕克菲尔德重复地震的压力下降？ （3）需要哪些数据质量和分析要求来确认在此处和未来的研究中观察到的空间和时间变化是真实的？拟议的研究将增加对帕克菲尔德及其他地区地震源过程的理解。开发的方法以及对它们的局限性和约束的更深入的理解，应使地震来源参数更高分辨率，因此，全球范围内的地震危害图。