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: 1547083
• 负责人: Rachel Abercrombie
• 金额: $ 15.87万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Continuing 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=1547083&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.

必须改进对地震危险的估计，以减少每年地震造成的重大人员和财政损失。地震期间释放的应力（称为应力降）控制着地震波产生的地面加速度，从而控制着潜在的破坏。应力降也是理解和模拟震源物理的基础，因为它定义了能量收支。重要的是要知道应力降是否因地区而异，并与地震震级。这是因为高地震活动性地区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地区的危险，例如具有诱发地震活动的地区。然而，目前还不清楚地震之间的应力降到底有多大变化。所观察到的变化范围超过100至1000倍，这对解释应力降结果提出了重大挑战。通常不清楚有多少变异性来自测量不确定性，以及有多少代表断层性质的真实的区域变化。调查人员将重点关注加州中部帕克菲尔德附近的圣安德烈亚斯断层部分，那里地震发生率很高，包括明显的小重复地震序列，断层也蠕动缓慢。这是世界上最好的仪器故障部分之一。该奖项将通过支持一名职业女性PI和一名研究生，帮助俄克拉荷马州大学发展一个新的物理学小组。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，该州由于地震活动的急剧增加，对地震危险的认识有所提高，并将纳入课堂活动，大量的地震和长期密集的地震仪网络使该地区成为了解震源物理的天然实验室。多尺度密集观测网络提供了广泛的震级范围内的尺度记录;现有的详细研究提供了解释结果的明确背景。研究人员建议将多尺度（大尺度和小尺度）分析方法应用于密集的地震波形数据集，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。这项工作将集中在三个不同的问题：（1）是明显的缩放应力降的伪影的不良数据与有限的带宽，有限的震级范围，以及不充分的纠正网站和传播的影响？(2)帕克菲尔德重复地震的应力降是否会因2004年帕克菲尔德6级地震的应变率变化而随时间变化？(3)需要什么样的数据质量和分析要求来确认在这里和未来的研究中观察到的空间和时间变化是真实的？拟议中的研究将增加对帕克菲尔德及其他地区震源过程的了解。所开发的方法以及对其局限性和制约因素的更好理解应能提高震源参数的分辨率，从而提高全世界地震危险图的分辨率。