Investigation of the earth's mantle plumbing system at the global scale using an advanced seismic imaging approach.

使用先进的地震成像方法在全球范围内研究地幔管道系统。

• 批准号: 1417229
• 负责人: Barbara Romanowicz
• 金额: $ 25.95万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1417229&HistoricalAwards=false
• 关键词: Investigation; earth; mantle; plumbing; system

Improving the resolution of earth's mantle structure through seismic imaging is important for our understanding of the deep dynamic processes that are reflected in surface tectonics and ultimately give rise to earthquakes and volcanic eruptions. Seismic tomography utilizes seismic waves originating from natural earthquakes to illuminate the earth's interior using similar principles as used in medical imagery. While the long wavelength, smooth structure is now well documented, we strive to sharpen the picture and resolve smaller scale features that will help understand in detail how the internal circulation drives the motions of tectonic plates, and vice-versa, and obtain a better view of how heat is channeled from the deep interior to the surface, resulting not only in the system of volcanoes mid-ocean ridges but also in mid-plate volcanoes called "hotspots", such as the Hawaiian chain. Because hotter than average regions correspond to low seismic velocities, which are particularly difficult to image, their accurate imaging has not been possible until recently, with the advent of numerical methods to accurately compute the seismic wavefield propagation across the earth's mantle. This project builds upon our recent efforts to develop global seismic images of the entire mantle using such computations, and improve the sharpness of these images.The main goal of this project is to finalize the construction of higher resolution (up to 200-400 km laterally) global 3D radially anisotropic shear velocity model of the whole mantle based on a time domain waveform inversion approach that has so far been applied only to the upper mantle, with promising results. This waveform inversion methodology builds upon 20 years of experience of the PI in waveform tomography using mode-based wavefield computations, as well as two generations of global upper mantle shear velocity models developed using long period fundamental mode and overtone waveforms (periods 60s) and numerical wavefield computations (Spectral Element Method). In order to resolve lower mantle structure, isolating wavepackets that contain body wave energy is necessary, therefore we propose to extend the period range of our dataset to 30s - this will also increase spatial resolution further in the upper mantle, while keeping computations manageable. Further goals of the proposal are to (1) obtain higher resolution in the lateral variations of radial anisotropy throughout the mantle, (2) test the sensitivity of the 30 s dataset to inversion for a global averaged S/P velocity conversion factor and (3) collect additional, shorter window (~30mn after origin time) waveforms down to 20s to include more P wave energy and perform additional iterations to obtain a global P velocity model of the lower mantle.

通过地震成像提高地幔结构的分辨率对于我们理解反映在地表构造并最终引起地震和火山喷发的深层动力过程非常重要。地震断层扫描利用源自自然地震的地震波来照亮地球内部，其原理与医学成像中使用的原理类似。虽然长波长、光滑的结构现已得到充分记录，但我们努力锐化图像并解析较小尺度的特征，这将有助于详细了解内部循环如何驱动构造板块的运动，反之亦然，并获得更好的视图热量如何从内部深处传导到地表，不仅形成洋中脊火山系统，而且形成被称为“热点”的中板火山，例如夏威夷火山链。由于比平均温度更高的区域对应的地震速度较低，因此特别难以成像，直到最近，随着精确计算穿过地幔的地震波场传播的数值方法的出现，它们的精确成像才成为可能。该项目建立在我们最近利用此类计算开发整个地幔的全球地震图像并提高这些图像的清晰度的努力的基础上。该项目的主要目标是最终完成更高分辨率（横向高达200-400公里）的构建）基于时域波形反演方法的整个地幔的全局 3D 径向各向异性剪切速度模型，迄今为止仅应用于上地幔，并取得了有希望的结果。这种波形反演方法建立在 PI 使用基于模式的波场计算在波形层析成像方面 20 年的经验以及使用长周期基模和泛音波形（周期 60 秒）和数值开发的两代全球上地幔剪切速度模型的基础上。波场计算（谱元法）。为了解析下地幔结构，隔离包含体波能量的波包是必要的，因此我们建议将数据集的周期范围延长到30秒——这也将进一步提高上地幔的空间分辨率，同时保持计算的可管理性。该提案的进一步目标是（1）在整个地幔径向各向异性的横向变化中获得更高分辨率，（2）测试 30 s 数据集对全球平均 S/P 速度转换因子反演的敏感性，以及（3 ）收集额外的、较短的窗口（起始时间后约 30mn）波形至 20 秒，以包含更多的 P 波能量并执行额外的迭代以获得下地幔的全局 P 速度模型。