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Using Seafloor Compliance to image the Crust around Hawaii

使用海底顺应性对夏威夷周围的地壳进行成像

基本信息

批准号：
1736516
负责人：
Gabriele Laske
金额：
$ 26.08万
依托单位：
University of California-San Diego Scripps Inst of Oceanography
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-01 至 2020-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736516&HistoricalAwards=false
关键词：
Using Seafloor Compliance image Crust

项目摘要

Hawaii has long been the textbook example of a hotspot, where Earth's convecting mantle allows hot mantle rock to ascend through a relatively narrow and isolated mantle plume. This ascending material ultimately erupts at the surface in Hawaii's volcanoes. One of the most challenging questions concerns the geometry of a plume. In laboratory tanks that are heated from below, plumes are usually vertical and straight. But in a convecting spherical Earth, plumes should have more complex geometries. A key tool to trace plumes through Earth's mantle is seismic imaging. To image the Hawaiian plume, the PLUME seismic experiment (Plume-Lithosphere Undersea Melt Experiment) deployed 80 seismometers in a 1000 km array across the Hawaiian region from 2005 to 2007 to collect earthquake data. Initial seismic tomographic images trace the plume down to 1000 km depth and reveal a complex geometry. One of the most surprising results is that the mantle plume appears to approach the surface from the west and not from the southeast as is commonly assumed. To draw more definitive conclusions however, the initial mantle images must be improved by removing the distorting effects caused by complex features in Earth's crust, which were ignored in the initial processing. This project will examine a new type of data called seafloor compliance, which is the deformation of the seafloor due to pressure variations from long period ocean waves that pass by the stations. This deformation or compliance strongly depends on the specific type of crustal rock beneath the station. By analyzing seafloor compliance, the project will catalog new and crucial details of Hawaii's crustal structure and refine the plume imaging. In terms of broader impacts, this project will support a graduate student and will make research results accessible to the wider community through teaching and public lectures. Dedicated small projects will be used as recruiting tool for undergraduate students to raise awareness in the Earth sciences and related fields.Hawaii's location far from any plate boundary provides an opportunity to test basic hypotheses regarding plume/plate interaction and related magmatism. Initial seismic tomography conducted for the Plume-Lithosphere Undersea Melt Experiment (PLUME) has revealed the first high-resolution 3-D images that support the presence of a deep-rooted mantle plume, but the complexity of findings motivate a revision of the classic plume concept. Some aspects of seismic imaging remain controversial, specifically the continuity of the plume within the mantle, its interaction with the mantle transition zone and the exact magma pathways in the very shallow mantle and crust. A potential problem with published models is that mantle images were produced assuming a relatively simple crustal architecture. Even rather modest changes in crustal structure can profoundly impact the imaging of regions beneath, and may even cascade downward into the lower mantle. Artifacts in the mantle images may lead to false conclusions about geodynamical, geochemical and geological processes that ultimately cause Hawaii's volcanism. This project focuses on combining shallow-focus seismic datasets to illuminate Hawaii's crust and shallowest mantle. The primary dataset is seafloor compliance, the transfer function between pressure exerted by passing infragravity waves and the resulting seafloor deformation. Seafloor compliance is particularly sensitive to shear velocity in the ocean sediments. These new data will be combined with other crust-sensitive datasets such as high-frequency Rayleigh wave dispersion maps, crustal receiver functions and ambient-noise Empirical Green's Functions. The resulting new crustal model will allow revision of mantle models and plume geometry with much more fidelity than is currently available.

夏威夷长期以来一直是热点的教科书范例，在那里，地球的对流地幔允许热地幔岩石通过相对狭窄和孤立的地幔柱上升。这些上升的物质最终会在夏威夷火山的表面喷发。最具挑战性的问题之一是羽流的几何形状。在从下面加热的实验室储罐中，羽流通常是垂直和直的。但在一个对流的球形地球上，羽流应该有更复杂的几何形状。通过地幔追踪地幔柱的关键工具是地震成像。为了对夏威夷羽流进行成像，羽流-岩石圈海底融化实验（plume earthquake experiment）从2005年到2007年在夏威夷地区部署了80个地震仪，在1000公里的阵列上收集地震数据。最初的地震层析成像图像可以追踪到1000公里深处的羽流，并显示出复杂的几何形状。最令人惊讶的结果之一是，地幔柱似乎是从西边接近地球表面的，而不是通常认为的从东南方向。然而，为了得出更明确的结论，必须通过消除地壳复杂特征造成的扭曲效应来改进初始地幔图像，而这些扭曲效应在初始处理中被忽略了。该项目将研究一种称为海底顺应性的新型数据，即由于经过监测站的长周期海浪的压力变化而导致的海底变形。这种变形或顺应在很大程度上取决于台站下面特定类型的地壳岩石。通过分析海底顺应性，该项目将对夏威夷地壳结构的新关键细节进行编目，并改进羽流成像。就更广泛的影响而言，该项目将支持一名研究生，并将通过教学和公开讲座使更广泛的社区获得研究成果。专门的小型项目将被用作招募本科生的工具，以提高对地球科学和相关领域的认识。夏威夷远离任何板块边界的位置，为检验有关地幔柱/板块相互作用和相关岩浆作用的基本假设提供了机会。为羽流-岩石圈海底熔融实验（PLUME）进行的初步地震层析成像显示，第一张高分辨率的3d图像支持了深根地幔羽流的存在，但研究结果的复杂性促使人们对经典的羽流概念进行修订。地震成像的一些方面仍然存在争议，特别是地幔内羽流的连续性，它与地幔过渡带的相互作用以及非常浅的地幔和地壳中的确切岩浆路径。已发表模型的一个潜在问题是，地幔图像是在假定地壳结构相对简单的情况下生成的。即使是地壳结构上相当微小的变化，也会深刻地影响地下区域的成像，甚至可能向下影响到下地幔。地幔图像中的人工制品可能会导致对地球动力学、地球化学和地质过程的错误结论，这些过程最终导致夏威夷的火山活动。这个项目的重点是结合浅层地震数据集来阐明夏威夷的地壳和最浅层地幔。主要数据集是海底顺应性，即通过亚重力波施加的压力与由此产生的海底变形之间的传递函数。海底顺应性对海洋沉积物的剪切速度特别敏感。这些新数据将与其他地壳敏感数据集相结合，如高频瑞利波色散图、地壳接收函数和环境噪声经验格林函数。由此产生的新地壳模型将使地幔模型和地幔柱几何形状的修正具有比目前可用的更高的保真度。