EAGER: Spatio-temporal Imaging of Mount St. Helens Magmatic System using Efficient Waveform Inversion of Earthquake Records

圣海伦斯火山位于卡斯卡迪亚俯冲带，是一座活火山，因其1980年的毁灭性喷发而闻名，该火山被广泛认为是美国历史上造成人员伤亡和基础设施破坏最严重的火山喷发。事实上，美国地质调查局（USGS）认为圣海伦火山是一个非常高的威胁火山。这里计划的工作将阐明圣海伦火山的岩浆管道系统，并帮助科学家更好地预测即将发生的火山活动及其可能的持续时间。这些知识将对减轻火山危害和帮助拯救人类生命极为有用。该项目是一所大学（科罗拉多矿业学院）和政府机构（美国地质勘探局）之间的合作，旨在扩展一项尖端技术的应用，该技术最初是由一家私营企业（地震科学有限责任公司）开发的，用于对油气储层的水力裂缝进行成像，以监测火山系统，以改善社会。研究人员认为，此次合作将促进油气行业与政府机构之间的进一步合作、技术转让和思想交流。在这个项目下开发的过程和技术有可能扩展到其他俯冲带，以帮助成像世界各地的大型逆冲断层和火山系统。人们对圣海伦火山岩浆系统的构造以及岩浆产生、运输和储存的时空变化知之甚少。为了解决这些问题，在过去的三十年里，作为EarthScope项目的一部分，以主动地震调查和被动地震记录的形式获得了大量的地震数据。研究人员将使用本地地震记录，包括活动地震数据（包括两个节点检波器阵列和PASSCAL德克萨斯检波器）和宽带地震仪，以及活动地震波形数据，通过波形反演生成St. Helens火山岩浆系统的高分辨率延时三维图像。这些图像将从浅层上地壳一直延伸到圣海伦火山下的俯冲板块，从而有助于阐明岩浆系统的完整结构、不同岩浆体之间的联系以及岩石的物理状态。了解圣海伦火山的岩浆系统（就其结构和时空变化而言）将为许多关键的科学挑战提供有价值的见解，包括地壳演化、地幔中的岩浆生成、岩浆从上地幔到浅层地壳的运输、岩浆储层结构和火山活动预测等问题。高分辨率的时空三维图像对于理解与岩浆侵位/膨胀相关的应力变化以及破译地壳和上地幔中熔体的运输将特别有用。此外，圣海伦火山地壳和地幔岩浆的规模、范围和连通性也没有完全确定。对地壳深部和上地幔的高分辨率图像，一直到板块，将有助于详细揭示大规模岩浆系统，揭示俯冲板块的复杂细节，地幔楔的蛇纹化可能性，以及地幔弧前莫霍体的弱反射率。该项目中使用的波形处理和反演技术最初是由Seismic Science LLC开发的，用于绘制低渗透油气地层水力压裂过程中产生的裂缝。在这个项目中，科罗拉多矿业学院和美国地质调查局（USGS）将合作使用这项技术对圣海伦火山岩浆系统进行高分辨率成像。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。

Mount St. Helens, in the Cascadia Subduction Zone, is an active volcano and is most well known for the devastating 1980 eruption which is widely regarded as the most disastrous volcanic eruption in the United States history in terms of loss of human life and damage to infrastructure. In fact, the United States Geological Survey (USGS) regards Mount St. Helens as a very high threat volcano. The work planned here will illuminate the Mount St. Helens magmatic plumbing system and help scientists better forecast impending volcanism and its possible duration. Such knowledge will be extremely useful for volcanic hazard mitigation and help save human lives. This project is a collaboration between a university (Colorado School of Mines) and a government institution (USGS) to extend the application of a cutting-edge technology, originally developed by a private enterprise (Seismic Science LLC) to image hydraulic fractures in oil & gas reservoirs, for monitoring volcanic systems for the betterment of the society. The investigators believe this collaboration will foster further cooperation, technology transfer, and exchange of ideas between the hydrocarbon industry and government entities. The processes and techniques developed under this project could potentially be extended to the other subduction zones in order to help image megathrust and volcanic systems all over the world.The architecture of the Mount St. Helens magmatic system and the spatio-temporal changes resulting from magma production, transport, and storage are poorly understood. To address these questions, extensive seismic data, in the form of active-seismic surveys and passive recordings, have been acquired over the past three decades and also as part of the EarthScope program. The investigators will use local earthquake recordings from both the active-seismic data (comprising of two nodal geophone arrays and PASSCAL Texan geophones) and broadband seismometers and the active-seismic waveform data to generate a high-resolution time-lapse 3-dimensional image of the Mount St. Helens magmatic system using waveform inversion. These images will extend from the shallow upper-crust all the way to the subducting slab underneath Mount St. Helens, thereby helping to shed light on the complete architecture of the magmatic system, the connections between different magma bodies, and the physical state of the rocks. Knowledge of the magmatic system at Mount St. Helens (in terms of its architecture and spatio-temporal changes) will provide valuable insight into a number of key scientific challenges including questions about crustal evolution, magma generation in the mantle, magma transport from the upper mantle to the shallow crust, the structure of magma reservoirs, and forecasting volcanism. The high-resolution spatio- temporal 3-dimensional images will be especially useful in understanding stress changes associated with magma emplacement/inflation and in deciphering the transport of melts in the crust and upper mantle. Also, the scale, extent, and connectivity of magma in the crust and mantle beneath Mount St. Helens is not fully established. High-resolution images of the deep crust and upper mantle, all the way to the slab, will help unravel the large-scale magmatic system in detail and will reveal intricate details of the subducting slab, the possibility of serpentinization of the mantle wedge, and the weak reflectivity of the Moho in the mantle fore- arc. The waveform processing and inversion technology employed in this project was originally developed at Seismic Science LLC for mapping fractures generated during hydraulic stimulation of low-permeability oil and gas formations. Under this project, Colorado School of Mines and United States Geological Survey (USGS) will collaborate to employ this technology to image the Mount St. Helens magmatic system at high resolution.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.