Collaborative Research: Magnetotelluric and Seismic Investigations of the Distribution of Magmatic and Hydrous Fluids Beneath Yellowstone

合作研究：大地电磁和地震对黄石地下岩浆和水流体分布的调查非技术描述爱达荷州、蒙大拿州和怀俄明州的黄石火山系统在过去210万年里产生了三次大规模火山喷发，最近一次是64万年前。直到7万年前才有较小规模的喷发，而今天，黄石公园的火山系统拥有一个动态的热液系统，每年都会发生数千次小规模地震。在这个项目中，威斯康星大学麦迪逊分校和俄勒冈州立大学的一个团队正在黄石国家公园及其周围部署一个敏感的大地电磁(MT)设备网络，记录地球地磁场和地电场的自然变化。该团队正在使用MT数据来感知地壳和地幔传导性的微小变化，并通过结合MT和地震测量黄石下的结构，推断岩浆系统中流体的分布；岩浆在黄石公园的储存方式；以及它在该地区的移动性。这对黄石公园未来的火山活动和这种活动可能带来的潜在危险有影响。该项目还促进了首席研究员宁法·本宁顿的职业生涯，她是一名职业生涯早期的女科学家，涉及来自传统上代表性较低群体的研究生和本科生的实地工作。该团队正在创建外展材料，每年将通过威斯康星大学麦迪逊分校地质博物馆的互动信息亭与超过4万人分享，并正在开发一款智能手机应用程序，以与更广泛的受众分享这些内容。此外，他们正在与黄石国家公园合作，为国家公园网站创建详细介绍所进行的实地工作和项目结果的内容。这些努力将确保这一项目的成果被广泛接受。以前对黄石公园(YS)下地壳和上地幔进行的地震和大地电磁(MT)研究为岩浆流体进入YS地壳火山系统的起源和迁移提供了洞察。然而，关于YS岩浆作用的产生以及这些岩浆流体在地壳火山系统内的迁移和储存，仍然存在重要的问题。研究小组提出了三种相互竞争的假说来描述YS的活火山作用，其中包括对以下问题的不同解释：1)上地幔/下地壳深度的岩浆流体的来源和位置；2)这些岩浆流体进入中上地壳的首选路径；3)由此产生的岩浆储集层的分布；4)岩浆储集层的组成；以及5)对YS未来火山作用的影响。为了评估YS活火山活动的这些假设，该团队正在YS地区进行高分辨率的大地电磁测量，并将这些观测与现有数据结合起来，以反演YS下方地壳和上地幔的3D电阻率结构。该团队还在使用多尺度技术分别反演地震数据，以确定同一地区的地震速度结构。所得到的模型对地下的不同性质很敏感(例如，MT对熔体的存在和地震速度对温度的升高)，因此提供了独立的结构约束。该团队将通过联合解释将这些独立的、空间上重合的模型结合在一起，测试它们关于黄石岩浆系统中岩浆和相关流体的分布和行为的假设。

Collaborative Research: Magnetotelluric and Seismic Investigations of the Distribution of Magmatic and Hydrous Fluids Beneath YellowstoneNon-technical descriptionThe Yellowstone volcanic system in Idaho, Montana, and Wyoming has produced three massive volcanic eruptions in the past 2.1 million years, the most recent 640,000 years ago. Smaller eruptions followed until 70,000 years ago, and today, Yellowstone's volcanic system hosts a dynamic hydrothermal system with thousands of small magnitude earthquakes occurring annually. In this project, a team from the University of Wisconsin-Madison and Oregon State University is deploying a network of sensitive magnetotelluric (MT) equipment, which record natural variations in Earth's geomagnetic and geoelectric fields, in and around Yellowstone National Park. The team is using MT data to sense small changes in conductivity of the crust and mantle and, by combining MT and seismic measurements of the structure beneath Yellowstone, the team will infer the distribution of fluids in the magmatic system; how magma is stored at Yellowstone; and how mobile it is within the region. This has implications for future volcanic activity at Yellowstone and potential hazards such activity might pose.This project is also fostering the career of principal investigator Ninfa Bennington, an early career female scientist, and involves field work by both graduate and undergraduate students from traditionally underrepresented groups. The team is creating outreach materials that will be shared with more than 40,000 people per year via interactive kiosks at the Geology Museum of the University of Wisconsin-Madison, and is developing a smartphone app to share this content with an even broader audience. In addition, they are working with Yellowstone National Park to create content detailing the field work carried out, and the results of the project, for the National Park Web site. These efforts will ensure the results from this project reach a wide audience.Technical Description of ProjectPrevious seismic and magnetotelluric (MT) studies of the crust and upper mantle beneath Yellowstone (YS) have provided insight into the origin and migration of magmatic fluids into the YS crustal volcanic system. However, important questions remain concerning the generation of magmatism at YS and the migration and storage of these magmatic fluids within the crustal volcanic system. The research team has developed three competing hypotheses describing active volcanism at YS, which include different explanations for: 1) the origin and location of magmatic fluids at upper mantle/lower crustal depths 2) the preferred path of migration for these magmatic fluids into the mid- to upper-crust, 3) the resulting distribution of the magma reservoir, 4) the composition of the magma reservoir, and 5) implications for future volcanism at YS. To evaluate these hypotheses for active volcanism at YS, the team is conducting a high-resolution MT survey in the YS region, and is combining those observations with existing data to invert for the 3D resistivity structure in the crust and upper mantle underneath YS. The team is also separately inverting seismic data to determine the seismic velocity structure in the same region using multi-scale techniques. The resulting models are sensitive to different properties of the subsurface (e.g., MT to presence of melt and seismic velocity to increased temperature), and therefore provide independent structural constraints. The team will combine these independent, spatially coincident models through joint interpretations test their hypotheses about the distribution and behavior of magmatic and related fluids in the Yellowstone magmatic system.