RAPID: Collaborative Research: Response to the 2016 M5.8 Pawnee Earthquake: Using MT to map Fluids in Faults

自2008年以来，与主要石油和天然气业务相关的美国中部地震活动急剧增加。俄克拉荷马州现在被认为是地震最活跃的州之一。一些地震发生在人口稠密的城市附近，也发生在国家安全级别较高的地区，如俄克拉荷马州的库欣，这是美国石油和天然气管道运输系统的主要枢纽。与加州和阿拉斯加的地震不同，加州和阿拉斯加的地震可以明显地与板块边界的变形联系在一起，俄克拉荷马州的地震原因仍然是一个非常有争议的话题。然而，越来越多的科学证据表明，地震活动水平的提高与注入与石油开采有关的钻探活动产生的含盐废水有关。尽管地震台网能够探测活动并绘制其震中地图，但它们无法成像负责触发地震活动的断层中流体的分布。大地电磁(MT)技术是利用在S地表测量到的自然产生的电场和磁场来测量导电结构。2016年俄克拉荷马州波尼5.8级地震为科学家提供了一个前所未有的机会，将地震活动与断层上或断层周围流体的成像联系起来。因此，我们将通过断层最近破裂和地震活动集中的地区以及附近没有破裂的断层进行一系列二维(2D)剖面。将我们的结果与正在进行的地震研究相结合，将有助于更好地理解流体注入和地震活动之间的联系。这项研究的结果可以为决策者的决策提供参考。电法地球物理方法非常适合于成像含流体断层，因为产出的水是高度含盐的，因此具有很高的导电性。到目前为止，还没有研究对俄克拉荷马州断层中的流体进行成像，并将其与地震活动直接联系起来。几口注水井位于震中半径20公里范围内；研究表明，在大流量井中注入流体可能会引发远至30公里的地震。这项提议将收集MT地球物理数据，这些数据将限制在2016年波尼5.8级地震期间破裂的断裂带中流体的分布。由于大多数注入活动在2016年9月3日地震后暂时停止，我们有独特的机会在系统被额外的废水注入改变之前捕捉到流体诱发地震活动过程的状态。鉴于俄克拉荷马州的地震活动遭到了公众的强烈抗议，立法者要求采取行动。然而，利益相关者和政策制定者的任何决定都必须以可靠的科学和不偏不倚的数据为指导。根据地质情况确定诱发地震活动的特征，以便纳入地震危险性评估，这对敏感设施的评估至关重要。因此，我们建议的MT调查具有多方面的更广泛的影响：(1)它将产生数据受限的结果，从而更好地了解废水的迁移？断层相互作用。(2)我们将提供相关数据，供政策制定者和利益攸关方在评估与废水注入有关的地震危害时参考。(3)我们的项目将吸引几个学生。学生将协助获取数据，并将从大地电磁专家那里获得如何部署大地电磁仪器的实践经验。至少有两名学生将来自代表性不足的群体，从而在科学和工程领域建立一支多元化的劳动力队伍

Since 2008, there has been a dramatic increase in earthquake activity in the central United States in association with major oil and gas operations. Oklahoma is now considered one of the most seismically active states. Some of the earthquakes are occurring near populated cities and also in areas of high national security such as Cushing, Oklahoma, a major hub of the U.S. oil and gas pipeline transportation system. Unlike earthquakes in California and Alaska that can be clearly linked to deformation along plate boundaries, the cause of the earthquakes in Oklahoma remains a very contentious and highly debated topic. However, there is an increasing body of scientific evidence to suggest that the increased level of seismicity is linked to the injection of saline production wastewaters from drilling activity related to petroleum exploitation. Although seismic networks are able to detect activity and map its hypocenter, they are unable to image the distribution of fluids in the fault responsible for triggering seismicity. The magnetotelluric (MT) technique, uses naturally occurring electric and magnetic fields measured at Earth?s surface to measure conductivity structure. The 2016 M5.8 Pawnee, Oklahoma earthquake provides an unprecedented opportunity for scientists to provide a link between seismicity and imaging of fluids on or around faults. Thus we will carry out a series of two-dimensional (2D) profiles located through areas where the fault recently ruptured and seismic activity is concentrated and also across the faults in the vicinity that did not rupture. The integration of our results and ongoing seismic studies will lead to a better understanding of the links between fluid injection and seismicity. Results of this study can inform decisions by policy-makers. Electrical geophysical methods are ideally suited to image fluid bearing faults since the produced waters are highly saline and hence have a high electrical conductivity. To date, no study has imaged the fluids in the faults in Oklahoma and made a direct link to the seismicity. Several injection wells are located within a 20 km radius of the epicenter; and studies have suggested that injection of fluids in high-volume wells can trigger earthquakes as far away as 30 km. This proposal will collect MT geophysical data that will constrain the distribution of fluids in the fault zone that ruptured during the 2016 M5.8 Pawnee earthquake. Because most injection activities have been temporarily suspended following the September 3, 2016 earthquake, we have the unique opportunity to capture the state of the fluid induced seismicity process before the system is altered by additional wastewater injection. Given that seismicity in in Oklahoma has been met with public outcry, with demands for action by legislators. However, any decision by stakeholders and policy makers must be guided by sound science and unbiased data. Geologically informed approaches to characterizing induced seismicity for inclusion in seismic hazard evaluations is critical for evaluation of sensitive facilities. As a result, our proposed MT survey has multi-faceted broader impacts: (1) It will produce data-constrained results that will lead to a better understanding of migration of wastewater ? fault interactions. (2) We will produce relevant data that can be used to inform the decisions of policy-makers and stakeholders when assessing seismic hazards related to wastewater injection. (3) Our project will engage several students. Students will assist with the data acquisition and will gain hands-on experience from MT experts in how to deploy MT instrumentation. At least two of the students will come from under-represented groups, thereby building a diverse workforce in science and engineering