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一个热点的教科书示例，地球上的地幔使热地幔岩石可以通过相对狭窄且孤立的地幔羽上升。这种上升的材料最终在夏威夷火山的地面爆发。最具挑战性的问题之一是羽流的几何形状。在从下方加热的实验室储罐中，羽流通常是垂直而直的。但是，在令人信服的球形地球中，羽毛应该具有更复杂的几何形状。追踪羽毛在地球地幔中的关键工具是地震成像。为了成像夏威夷羽流，从2005年到2007年，羽状地震实验（羽流实验实验）在整个夏威夷地区的1000公里阵列中部署了80台地震米，以收集地震数据。最初的地震层析成像图像将羽流向下追踪至1000公里的深度，并揭示复杂的几何形状。最令人惊讶的结果之一是，地幔羽似乎从西部接近表面，而不是通常从东南部接近地面。然而，为了得出更确定的结论，必须通过消除由地壳中复杂特征引起的扭曲效果来改善初始地幔图像，而地壳中的复杂特征在初始处理中被忽略了。该项目将检查一种称为海底合规性的新类型的数据，这是由于站点经过的长时间海浪的压力变化而导致海底的变形。这种变形或依从性在很大程度上取决于站点下面的地壳岩石的特定类型。通过分析海底合规性，该项目将分类夏威夷地壳结构的新的和关键的细节，并完善羽状成像。在更广泛的影响方面，该项目将支持研究生，并将通过教学和公共讲座使更广泛的社区获得研究结果。专门的小型项目将用作招聘工具，以供大学生提高地球科学和相关领域的认识。Hawaii远离任何板界的位置，都提供了一个机会，为测试有关羽流/板相互作用和相关岩浆的基本假设提供了机会。针对羽流圈海底融化实验（羽状）进行的最初的地震层析成像揭示了首个高分辨率的3-D图像，该图像支持了深根的地幔羽流，但发现的复杂性激发了经典羽流概念的修订。地震成像的某些方面仍然有争议，特别是地幔内羽流的连续性，与地幔过渡区的相互作用以及在非常浅的地幔和地壳中的确切岩浆途径。公开模型的一个潜在问题是，假设相对简单的地壳结构产生了地幔图像。即使是地壳结构的适度变化也会深刻影响下面区域的成像，甚至可能向下层叠到下层。地幔图像中的伪影可能会导致关于最终导致夏威夷火山的地球动力学，地球化学和地质过程的错误结论。该项目着重于将浅焦点地震数据集结合起来，以阐明夏威夷地壳和最浅的地幔。主要数据集是海底依从性，通过通过超级河流波和所得的海底变形所施加的压力之间的传递函数。海底依从性对海洋沉积物中的剪切速度特别敏感。这些新数据将与其他对地壳敏感的数据集结合使用，例如高频瑞利波分散图，地壳接收器功能和环境噪声经验绿色的功能。由此产生的新地壳模型将允许对地幔模型和羽状几何形状进行修订，其保真度比当前可用的要多得多。