Collaborative Research: Capitalizing on EarthScope Transportable Array Data to Better Characterize Induced Seismic Sequences

在美国中部的注射点附近，有震感和破坏性的地震数量的增加引起了公众的注意。鉴于此，人们越来越需要更好地了解这些序列是如何发展的，并教育公众有关诱发地震活动的科学知识。问题是，美国中部和东部的台站密度低，这意味着使用标准的分析审查技术不容易识别许多小地震，而小地震的完整目录的缺乏极大地阻碍了诱发地震活动的研究。此外，虽然临时网络通常是在地震序列开始产生重大地震或感觉地震后部署的，但这些网络会错过诱发地震序列的开始。我们的解决方案是使用EarthScope可移动阵列的数据，建立更完整的目录，更好地描述诱发地震序列的全部特征（包括前后）。为了更好地了解诱发地震活动的源物理，我们建议通过应用新开发的频域检测算法和阵列可视化映射技术来系统地识别位于美国中部和东部流体注入点附近的当前未编录的小震级地震。使用新检测到的事件，我们将构建用作子空间检测器的模板波形目录。这些探测结果将用于为8个地理上分散的盆地建立更完整的目录。对这些增强的地震表进行分析，以解决以下问题：(1)在其他地震表没有显示地震活动的盆地中，是否存在可探测到的事件，或者有些盆地发生地震？(2)我们识别的模板事件在波形特征和/或位置上与先前编目的事件有多大程度的相似？(3)观测到的速率增加是否符合Gutenberg-Richter关系，b值是否有可预测的随时间变化？(4)相对较大的表面波通过的瞬态应力是否会动态触发额外的诱发事件或以其他方式改变诱发地震活动的分布？这项研究将更充分地开发频域检测算法和子空间探测器，用于识别小地震，并将用于创建比大多数现有地震目录完整程度更低的新地震目录（震级小于2.4）。这种大空间尺度的分析有可能提供有关诱发地震的新信息，并为不同地区普遍存在的诱发地震活动提供定量测量。

The increase in the number of felt and damaging earthquakes near injection sites in Middle America has the public's attention. Given this, there is an ever-growing need to better understand how these sequences develop and to educate the public about the science of induced seismicity. The problem is that the low station density in the central and eastern United States means that many small earthquakes are not easily identified using standard analyst review techniques, and the lack of a complete catalog of small earthquakes greatly impedes induced seismicity studies. Additionally, while temporary networks are often deployed after a sequence has started producing significant or felt earthquakes, these networks miss the initiation of the induced earthquake sequence. Our solution is to use data from the EarthScope Transportable Array, to establish more complete catalogs that better describe the full characteristics (both before and after) of induced seismic sequences. To obtain a better understanding of the source physics of induced seismicity, we propose to systematically identify currently uncataloged small magnitude earthquakes located near fluid injection sites in the central and eastern US by applying a newly developed frequency domain detection algorithm and array visualization mapping techniques to transportable array data. Using newly detected events, we will build a template waveform catalog for use as subspace detectors. The detections will be used to build more complete catalogs for eight geographically dispersed basins. These enhanced catalogs will be analyzed to address the following questions: (1) Are there detectable events in basins where other catalogs show no seismicity or are some basins aseismic? (2) To what extent are the template events we identify similar in waveform characteristics and/or location to previously cataloged events? (3) Are observed rate increases consistent with the Gutenberg-Richter relation and is there a predictable change in b-value with time? (4) Do transient stresses from the passage of relatively large surface waves dynamically trigger additional induced events or otherwise change the distribution of induced seismicity? This study will more fully develop frequency domain detection algorithms and subspace detectors tuned to identify small earthquakes, and will be used to create new earthquake catalogs with magnitude of completeness levels lower (magnitude less than 2.4) than most existing catalogs. This large spatial scale analysis has the potential to provide new information about induced earthquakes and provide a quantitative measure of the ubiquity of induced seismicity in different regions.