Collaborative Research: Systematic Analysis of Dynamic Earthquake Triggering Using the USArray Data

项目技术描述：尽管我们对地震破裂的物理原理的理解不断取得进展，但仍存在许多问题。一个基本问题是？是否存在触发地震的应力阈值（即振幅、频率、应力方向或震动持续时间）？我们建议检验与地震触发有关的两个假设：(1)存在触发远程地震所需的最小动应力阈值（即振幅、频率或两者）；(2)地震波通过引起的应力必须与局部应力场和断层走向有利对齐，才能触发地震。为了验证这些假设，我们将使用EarthScope？USArray可传输阵列（USArray TA）网络，可用时辅以本地地震台网数据。美国连续地区的USArray TA站的均匀间隔将使我们能够检查各种构造省份内的远程触发特征，背景地震活动率，以及记录的触发地震案例和未知触发地震地区的区域。对于每个TA站，我们将创建一个高频检测（HFD）目录。我们将采用三种统计检验（二项检验、Kolmogorov-Smirnov检验和Wilcoxon秩和检验）来确定地表波（或局部事件的s到达）后每个站点的HFD率变化的显著性。与IRIS的产品专家合作，我们将增强地震波场时间演变的地面运动可视化（GMV）电影，包括空间/时间标记，表示高频触发器和理论大圆路径的方向。我们将定性地检查这些可视化图像，寻找系统的远程地震触发信号。我们通过以下方法来验证我们的假设：(1)确定与每个高频触发点一致的地震波的峰值动应力和主导频率；(2)将通过地震波的方向与局部断层结构和应力场进行对比。对该项目更广泛意义和重要性的非技术解释：越来越多的科学研究表明，大地震发出的瞬态信号或地震波可以在距离大地震震中数千公里的地方远程引发小地震。我们将系统地调查触发使用数据收集EarthScope？美国的USArray可移动阵列（USArray TA）网络用于全球和区域地震，这可以为地震破裂的物理机制提供基本的见解。我们将提供工具和专业知识，以有效地挖掘大型USArray数据集（1000个站点，其中400个同时活跃；89,000次地震），用于目前未识别的触发地震。我们将按站点对这些触发事件进行分类，从而获得空间/时间记录以供进一步分析。我们还将开发交互式可视化工具，用于比较触发与地震波场的时空分布。我们将开发的方法，以及系统处理的主震数量，在理解地震触发过程方面具有变革性的潜力。德克萨斯大学埃尔帕索分校是一所西班牙裔服务学院（HSI），我们将积极招募本科生和研究生，以及一名来自代表性不足群体的博士后学者参与该项目。

Technical description of the project: Although advances are constantly being made in our understanding of the physics governing earthquake rupture, many questions remain. One fundamental question is ?Does a stress threshold exist (i.e., amplitude, frequency, stress orientation, or duration of shaking) for triggering earthquakes?? We propose to test two hypotheses related to earthquake triggering: (1) There exists a minimum dynamic stress threshold (i.e., in amplitude, frequency or both) required to trigger remote earthquakes; and (2) The stresses induced by the passage of seismic waves must align favorably with the local stress field and orientation of faults in order to trigger earthquakes. To test these hypotheses, we will use data collected by stations in EarthScope?s USArray Transportable Array (USArray TA) network, supplemented by local seismic network data when available. The uniform spacing of the USArray TA stations across the contiguous USA will allow us to examine characteristics of remote triggering within a variety of tectonic provinces, background seismicity rates, and within regions of both documented cases of triggered earthquakes and areas of no known triggered earthquakes. For each TA station we will create a catalog high-frequency detections (HFD). We will apply three statistical tests (Binomial, Kolmogorov-Smirnov and Wilcoxon Rank-sum) to determine the significance of HFD rate changes at each station following the surface waves (or S-arrival for local events). Working in tandem with Product Specialists at IRIS, we will augment Ground Motion Visualization (GMV) movies of the temporal evolution of the seismic wavefield to include spatial/temporal markers denoting high-frequency triggers and the orientation of theoretical great-circle paths. We will qualitatively examine these visualizations for signatures of systematic remote earthquake triggering. We test our hypotheses by: (1) Determining the peak dynamic stress and dominant frequency of the passing seismic waves coincident with each of the high-frequency triggers; and (2) Comparing the orientation of the passing seismic waves with the local fault structures and stress field.Non-technical explanation of the project's broader significance and importance: A growing body of scientific studies has demonstrated that the passage of transient signals, or seismic waves, from large earthquakes can remotely trigger small earthquakes thousands of kilometers from an epicenter of a large earthquake. We will systematically investigate triggering using data collected from EarthScope?s USArray Transportable Array (USArray TA) network for global and regional earthquakes, which could provide fundamental insight into the physical mechanisms of earthquake rupture. We will provide the tools and expertise to effectively mine the large USArray dataset (1,000 stations of which 400 are concurrently active; 89,000 earthquakes) for currently unrecognized triggered earthquakes. We will catalog these triggered events by station, thus having a spatial/temporal record for further analysis. We will also develop interactive visualization tools for comparing the spatial and temporal distribution of triggering to the seismic wavefield. The methodology we will develop, and the number of mainshocks systematically processed, have the potential to be transformative in terms of understanding earthquake triggering processes. The University of Texas at El Paso is a Hispanic Serving Institute (HSI) and we will actively recruit undergraduate and graduate students, plus a postdoctoral scholar from underrepresented groups to participate in this project.