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

为了减少每年在地震中遭受的重大人员和经济损失，有必要改进对地震危险的估计。地震中释放的应力（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随地区和地震震级而变化。这是因为高地震活动性地区的地震参数和地面震动测量经常用于估计其他可能具有较低历史地震活动性的地区的危险性，例如具有诱发地震活动性的地区。然而，目前还不清楚每次地震的压力下降究竟有多大差异。观察到的变异性范围在100到1000之间，这给解释应力下降结果带来了重大挑战。通常不清楚有多少可变性来自测量的不确定性，又有多少代表断层性质的实际区域变化。调查人员将把重点放在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，那里地震频发，包括明显的小地震重复序列，断层也缓慢爬行。它是世界上仪器设备最好的断层之一。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，帮助俄克拉何马大学建立一个新的地球物理学小组。学生将有机会成为波士顿和俄克拉何马州研究社区的积极参与者。这些研究活动将有助于在俄克拉何马州建立地震研究，由于地震活动的急剧增加，该州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宽震级范围的尺度记录；现有的详细研究为解释结果提供了一个定义良好的背景。研究者建议将多尺度（包括大尺度和小尺度）分析方法应用于地震波形的密集数据集，旨在解决关于地震尺度和变率的持续争议。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上：(1)应力下降的明显尺度是有限带宽、有限震级范围和对现场和传播效应校正不足的不良数据的产物吗？(2) 2004年M6帕克菲尔德地震应变速率的变化是否导致帕克菲尔德重复地震的应力降随时间变化？(3)需要什么样的数据质量和分析要求来证实本研究和未来研究中观测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震源过程的了解。所开发的方法，以及对其局限性和限制的更深入了解，应该能够提高震源参数的分辨率，从而在世界范围内绘制地震危险图。

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.