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

有必要改进对地震危险的估计，以减少每年在地震中遭受的重大人员和经济损失。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，从而控制着破坏潜力。应力降也是理解和模拟震源物理的基础，因为它定义了能量平衡。重要的是要知道应力降是否随地区不同而不同，并随地震震级而变化。这是因为地震高活动区的地震参数和地面震动测量经常被用来估计其他历史地震活跃率较低的地区的危险性，例如诱发地震活动的地区。然而，目前尚不清楚不同地震之间的应力降到底有多大。观测到的变异性范围在100到1000倍之间，这对解释应力降结果构成了巨大的挑战。人们往往不清楚，测量的不确定性在多大程度上带来了可变性，在多大程度上代表了断层性质的真实区域差异。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段，那里地震发生率很高，包括明显的小地震重复序列，而且断层也缓慢爬行。它是世界上仪器最好的断层段之一。该奖项将通过支持一名刚刚开始职业生涯的女性PI和一名研究生来帮助俄克拉荷马大学一个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荷马州建立地震研究，该州由于地震活动的急剧增加而提高了对地震危险的认识，并将被纳入课堂活动。大量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明确的背景。研究人员建议对密集的地震波形数据集应用多尺度(包括大尺度和小尺度)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。这项工作将集中在三个不同的问题上：(1)应力降的明显尺度是由于有限的带宽、有限的震级范围以及对场地和传播影响的校正不足而导致的糟糕数据的产物？(2)由于2004年帕克菲尔德6级地震的应变率的变化，帕克菲尔德重复地震的应力降是否随时间变化？(3)需要什么样的数据质量和分析要求才能证实在这里和未来研究中观察到的时空变化是真实的？这项拟议的研究将增加对帕克菲尔德内外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，应该能够在世界范围内更高分辨率地研究震源参数，从而绘制地震危险图。

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.