Probing the roots of active volcanic systems with spectral ambient noise tomography and receiver functions

火山是地球深处板块构造过程最明显的地表表现，对人类生命和财产构成重大威胁。 虽然火山的暴露和浅埋部分已被广泛研究，并相当了解，管道系统的更深的组成部分，从地球传输岩浆？众所周知，用传统的地球物理技术很难研究地球的地幔到地壳，因此更加神秘。 该项目旨在利用最近开发的一种技术探测几座活火山的深度，这种技术利用周围的地震噪音，以类似于制作人体超声波图像的方式对地球进行成像。 这项工作最初将集中在阿留申群岛和阿拉斯加库克湾附近的仪器齐全的火山。 一旦这些技术得到充分开发和测试，我们将把它们应用于现有的高质量地震数据集，这些数据集是在世界上其他火山活跃地区收集的，包括喀斯喀特山脉、夏威夷、冰岛和黄石公园。 这些结果有望帮助地质学家了解火山喷出的岩石是如何在地壳底部附近，在地球下方20-35公里深处产生和改变的？s表面。 此外，从这项工作中产生的基线结构模型将成为未来分析与喷发或其他主要岩浆事件有关的深层火山结构变化的宝贵资源。从玄武质母岩浆中提炼构成大陆地壳大部分的中间和长英质成分的关键过程被认为发生在火山弧的中地壳和下地壳，并可能发生在地震莫霍面之下。 然而，由于各种原因，下地壳是一个难以用主动和被动震源地震学家可用的工具成像的区域。该项目的目标是解决这样一些突出的科学问题：中等成分的大陆地壳是否形成于弧火山的中下地壳？深弧地壳的剪切速度结构是否揭示了与近地表中间岩互补的镁铁质/超镁铁质残余组分的存在？岩浆如何从上地幔迁移到热点火山的地壳浅层储层？我们将带来一种强大的新工具，对活动火山区下地壳和上地幔的详细地震和岩石学结构进行成像。该方法结合了环境噪声相关（ANC）和接收器功能分析的互补工具。ANC将剪切速度分解为深度的函数，并且对10-40公里深度范围内的速度特别敏感。从ANC函数提取相速度的一种新的谱方法允许使用比标准时域技术明显更短的路径，并且能够对空中有限的陆地块（例如单个火山）进行高分辨率成像。结合接收器功能，限制深度结构界面和Vp/Vs比，剪切速度从频谱ANC将被用来成像岩石圈结构下的几个火山。我们将分析来自阿拉斯加、喀斯喀特、夏威夷、黄石和冰岛火山的现有高质量宽带数据集，并测试基于文献中岩石学模型的正演模型。

Volcanoes are the most visible surface manifestations of plate tectonic processes operating deep within the earth, and pose a significant threat to human life and property. While the exposed and shallowly buried portions of volcanoes have been extensively studied and are fairly well-understood, the deeper components of the plumbing systems that transmit magma from the earth?s mantle to the crust are notoriously difficult to investigate using traditional geophysical techniques and are therefore much more enigmatic. This project aims to probe the depths of several active volcanoes using a recently developed technique that uses ambient seismic noise to image the earth in a manner analogous to that used to create ultrasound images of the human body. The work will initially focus on well-instrumented volcanoes in the Aleutian Islands and near Cook Inlet, Alaska. Once the techniques have been fully developed and tested, we will apply them to existing high-quality seismic data sets that have been collected in other volcanically active areas of the world including the Cascades, Hawaii, Iceland, and Yellowstone. The results are expected to help geologists understand how the rocks that are extruded at volcanoes are created and modified near the base of the crust, at depths of 20-35 km beneath the earth?s surface. Furthermore, The baseline structural models that will result from this work will form a valuable resource for future analyses of changes in deep volcanic structure related to eruptions or other major magmatic events. Critical processes involved with refining the intermediate and felsic compositions that make up the bulk of the continental crust from basaltic parent magmas are thought to occur in the middle to lower crust of volcanic arcs, and potentially beneath the seismic Moho. For a variety of reasons, though, the lower crust is a difficult region to image with the tools available to active and passive source seismologists. The goal of this project is to address such outstanding scientific questions as: Is intermediate-composition continental crust formed in the mid to lower crust of arc volcanoes? Does the shear velocity structure of deep arc crust reveal the presence of mafic/ultramafic residual fractions complementary to the near surface intermediate rocks? How does magma migrate from the upper mantle to shallow crustal reservoirs at hotspot volcanoes?We will bring a powerful new tool to bear on imaging the detailed seismic and, by extension, petrologic structure of the lower crust and upper mantle beneath active volcanic regions. The approach combines the complementary tools of ambient noise correlation (ANC) and receiver function analysis. ANC resolves shear velocities as a function of depth and is particularly sensitive to velocities in the 10-40 km depth range. A new spectral approach to extracting phase velocities from ANC functions allows the use of significantly shorter paths than standard time domain techniques and enables high resolution imaging of aerially limited land masses, such as individual volcanoes. Combined with receiver functions, which constrain the depth to structural interfaces and the Vp/Vs ratio, shear velocities from spectral ANC will be used to image the lithospheric structure beneath several volcanoes. We will analyze existing high quality broadband data sets from volcanoes in Alaska, the Cascades, Hawaii, Yellowstone, and Iceland, and test forward models based on petrologic models in the literature.This project is supported by the Geophysics and EarthScope Programs.