ER-PF: Using Distributed Acoustic Sensing for Tremor Detection and Site Characterization in Cascadia to Evaluate Earthquake Hazard

本奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。Manuel Mendoza被授予EAR博士后奖学金，在科罗拉多大学博尔德分校和科罗拉多矿业学院开展研究和教育计划。门多萨博士计划开发一种名为分布式声学传感（DAS）的地震监测新技术。DAS使用暗（未亮/未使用）现有的电信光缆，并将它们变成一种仪器，作为能够探测微小或遥远地震事件的网络。在美国太平洋西北部两个构造板块交汇的地方，发生大地震的条件很好，这可能导致海啸等其他危险。因此，需要大规模、连续的地震监测来评估即将发生的风险。在这个项目中，Mendoza博士将与Anne Sheehan教授和Ge Jin博士合作，通过在华盛顿西北部进行DAS实验来测试和展示DAS的性能。具体来说，这项工作将调查被称为“震颤”的地震事件，并确定光缆沿线的当地地质条件如何变化。门多萨博士的工作将促进人们对地震的理解，了解地面是如何对地震做出反应的，以及随之而来的地震危害。拟议的研究将为DAS在更大范围内与现有地震网络一起应用提供机会，以执行多学科和跨学科的研究和监测地球过程。该项目还将允许门多萨博士教授和指导来自代表性不足群体的学生，包括担任科罗拉多矿业学院多样性、包容性和准入委员会的导师，以及科罗拉多大学博尔德分校的暑期实习导师。与此项目相关的其他活动包括为地球物理学课程设计和领导当地的DAS实验，并监督一名本科生的专业和教育发展，该本科生将使用DAS数据进行原创性研究。在这两个校区，PI将参与旨在提高公众科学素养和扩大科学技术领域参与的外展活动。近年来，利用光纤测量地球地震扰动引起的形变（应变）的分布式声传感（DAS）已被证明是一种非常适用和有前途的地震学工具。这是因为它可以配置成一个孔径为几十公里的地震阵列，传感器（即通道）间距为米级，性能可与传统的宽带地震仪相媲美。这意味着DAS阵列可以覆盖大面积，同时在采样地震波场时不会受到空间混叠的影响（与传统网络不同），并以高保真度提供经常被遗漏的新信息。因此，单个DAS实验可用于同时研究发生在不同时空尺度上的各种地球过程。在这里，研究人员将在卡斯卡迪亚进行第一次已知的DAS实验，使用现有电信电缆的光纤来监测震颤并表征现场条件，以评估地震危害。具体来说，PI将追求三个主要的科学目标：(1)使用DAS探测和定位卡斯卡迪亚的震颤；(2)表征其时空行为，并推断其对板块界面上倾锁定部分的应力贡献；(3)确定沿DAS阵列的场址条件的米级变化。这些目标将通过采用基于地震阵列的技术，如波束形成和波束反向投影来捕捉地震，以及环境噪声干涉测量技术来估计顶部30米的横波速度（Vs30）来实现。本研究获得的结果将与使用不同仪器和方法进行的其他观测结果进行比较，以证明DAS在改进卡斯卡迪亚地震和地面震动模型方面的有效性，并评估其对未来各种构造环境实验的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Dr. Manuel Mendoza has been granted an EAR Postdoctoral Fellowship to carry out research and education plans at University of Colorado Boulder and Colorado School of Mines. Dr. Mendoza plans to develop a new technique for earthquake monitoring called distributed acoustic sensing (DAS). DAS uses dark (unlit/unused) existing telecommunication fiber optic cables and turns them into an instrument that acts as a network capable of detecting tiny or distant seismic (earthquake) events. In the Pacific Northwest of the US where two tectonic plates converge, the conditions are right for large earthquakes which could result in other hazards such as tsunamis. Therefore, large-scale and continuous seismic monitoring is needed to evaluate the impending risks. In this project, Dr. Mendoza will work alongside Professors Anne Sheehan and Dr. Ge Jin to test and demonstrate DAS performance capabilities by carrying out a DAS experiment in Northwestern Washington. Specifically, the work will investigate seismic events known as “tremor” and determine how local geologic conditions vary along the fiber cable. Dr. Mendoza’s work will advance understanding of earthquakes, how the ground shakes in response to them, and consequent seismic hazards. The proposed study will provide opportunities for DAS to be applied at larger scales alongside existing seismic networks to perform multi and interdisciplinary research and monitoring of Earth processes. The project will also allow Dr. Mendoza to teach and mentor students from underrepresented groups, including as a mentor on the Diversity, Inclusion, and Access committee at the Colorado School of Mines and as a summer internship mentor at University of Colorado Boulder. Other activities associated with this project include designing and leading a local DAS experiment for a geophysics course and supervising the professional and educational development of an undergraduate student who will conduct original research with the DAS data. At both campuses, the PI will engage in outreach activities aimed at increasing public scientific literacy and broadening participation in the S.T.E.M fields.Distributed acoustic sensing (DAS) using fiber-optics to measure deformation (strain) caused by seismic perturbations in the Earth has, in recent years, proved to be a highly applicable and promising tool in seismology. This is owed to its ability to be configured as a seismic array with an aperture on the order of tens of kilometers, meter-level sensor (i.e. channel) spacing, and performance comparable to that of conventional broadband seismometers. This implies that DAS arrays can blanket a large area while not suffering from spatial aliasing when sampling the seismic wavefield – unlike traditional networks – and provide new information in high fidelity that often goes missed. A single DAS experiment can therefore be used to simultaneously investigate a variety of Earth processes occurring across different spatial and temporal scales. Here, the investigators will conduct the first known DAS experiment in Cascadia using fiber from an existing telecommunication cable, to monitor tremor and characterize site conditions for the purpose of evaluating seismic hazard. Specifically, the PI will pursue three primary scientific goals: (1) Use DAS to detect and locate tremor in Cascadia; (2) characterize its spatiotemporal behavior and infer its contribution to stressing the up-dip locked portion of the plate interface; and (3) determine meter-level variation in site conditions along the DAS array. These goals will be addressed by employing seismic array-based techniques such as beamforming and beam back-projection to capture tremor, as well as ambient noise interferometry techniques to estimate shear wave velocities of the top 30 meters (Vs30). The results obtained from this study will be compared to other observations performed using different instruments and methods, to demonstrate the efficacy of DAS in improving earthquake and ground shaking models in Cascadia and assess its implications for future experiments in a variety of tectonic settings.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.