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。太平洋西北地区，特别是华盛顿州，以一个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，海底与北美大陆的地壳碰撞，并被推到地壳以下。大陆下海底的再循环是一个复杂的过程：海底的碰撞和下降会引起大地震、缓慢的滑动和震颤，以及火山爆发，比如在圣海伦斯山和堡垒山看到的火山爆发。为了了解这些潜在的破坏性过程，地球的内部结构需要在地震、流体释放和融化被触发的地方进行成像，深度可达地表以下200公里。探测地球内部的地震技术对大多数人来说都很熟悉，作为美国大范围地球观测计划的一部分，它们已被用于太平洋西北部。然而，地球成像的其他方法，如大地电磁（MT）方法，可以提供有关地球热结构的信息，并可以确定含有深层释放流体和熔融岩石的区域。MT使用闪电活动和太阳风-电离层相互作用产生的自然电流来估计地球的电导率。导电性部分取决于成分和温度，但只要少量的流体或熔体形成相互连接的网络，导电性就可以显著提高。EarthScope项目还在美国卡斯卡迪亚俯冲系统上建立了一系列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相关的一些关键问题。为了纠正这种情况，犹他大学和伍兹霍尔海洋研究所的科学家们正在收集华盛顿州中西部MT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。同一位置的地震数据将使联合解释这两种互补技术的技术得以发展，并将为了解Cascadia俯冲系统的演化提供见解。与这项研究相关的社会效益包括应用于理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，以及对研究生的培训。

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.