Collaborative Research: An Earthscope Magnetotelluric Survey of the Southern Cascadia Subduction System, Washington

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。太平洋西北部，特别是华盛顿州，以被称为卡斯卡迪亚俯冲系统的俯冲带环境为特征。卡斯卡迪亚俯冲系统是地球上的一个区域，海底正在碰撞，并被推到北美大陆覆盖的地壳之下。大陆下方海底的再循环是一个复杂的过程：海底的碰撞和下降可能导致大地震、缓慢滑动和震颤，以及圣海伦山和里道特山等火山爆发。为了了解这些潜在的破坏性过程，需要在地震、流体释放和融化的触发点对地球的内部结构进行成像，深度可达地表以下200公里。大多数人都熟悉用于探测地球内部的地震技术，它们已经作为美国范围内的地球镜计划的一部分在太平洋西北部使用。然而，其他地球成像方法，如大地电磁法，可以提供有关地球热结构的信息，并可以查明含有深层释放流体和熔融岩石的地区。MT使用自然发生的闪电活动和太阳风电离层相互作用产生的电流来估计地球的电导率。导电性反过来又部分取决于成分和温度，但只要它们形成一个相互连接的网络，少量的流体或熔体就可以显著增加导电性。EarthScope计划还在美国卡斯卡迪亚俯冲系统建立了一系列MT台站，但现有的覆盖范围缺乏空间分辨率，无法解决与俯冲带动力学有关的一些关键问题。为了纠正这种情况，来自犹他州大学和伍兹霍尔海洋研究所的科学家正在收集华盛顿州中西部MT台站的密集剖面，与先前记录的地震剖面相吻合，以纠正这种情况。共同定位的地震数据将有助于开发联合解释这两种互补技术的技术，并将有助于深入了解卡斯卡迪亚俯冲系统的演变。与这项研究相关的社会效益包括应用程序，以了解与卡斯卡迪亚俯冲系统相关的地震和火山灾害的过程，对研究基础设施的贡献，以及研究生的培训。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The Pacific Northwest, and Washington State in particular, are characterized by a subduction zone environment called the Cascadia subduction system. The Cascadia subduction system is an area of the Earth where the seafloor is colliding with, and is being pushed below the overriding crust of the North American continent. The recycling of the seafloor beneath the continent is a complex process: the collision and descent of the seafloor can cause major earthquakes, slow slip and tremor, and volcanic eruptions such as that seen at Mount St Helens and Mount Redoubt. In order to understand these potentially devastating processes, the internal structure of the Earth needs to be imaged at the point where earthquakes, fluid release and melting are triggered, to depths of up to 200 kilometers beneath the surface. Seismic techniques for looking into the Earth's interior are familiar to most people, and they have been used in the Pacific Northwest as part of the USA wide Earthscope program. However, other methods of imaging the Earth, such as the magnetotelluric (MT) method, can provide information regarding the thermal structure of the Earth and can pinpoint areas containing deep released fluids and molten rock. MT uses naturally occurring electric currents generated by lightning activity and by solar wind-ionospheric interactions, to estimate Earth's electrical conductivity. Conductivity in turn depends partly on composition and temperature, but it can be dramatically increased by small amounts of fluid or melt provided that they form an interconnected network. The EarthScope program has also established an array of MT stations over the U.S. Cascadia subduction system, but the existing coverage lacks the spatial resolution to address some of the key issues related to the dynamics of the subduction zone. To rectify this situation, scientists from the University of Utah and Woods Hole Oceanographic Institute are collecting a dense profile of MT stations across west-central Washington State coincident with a previously recorded seismic profile, to rectify this situation. The co-located seismic data will allow the development of techniques for jointly interpreting the two complementary techniques and will provide insights into the understanding of the evolution of the Cascadia subduction system. Societal benefits associated with this research include applications to understanding of processes that contribute to seismic and volcanic hazards associated with the Cascadia subduction system, contributions to research infrastructure, and training of graduate students.