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

通过地震成像提高地幔结构的分辨率对于我们理解地表构造所反映的深层动力过程并最终导致地震和火山爆发具有重要意义。地震层析成像利用源自自然地震的地震波来照亮地球内部，原理与医学成像类似。虽然长波长，光滑的结构现在已经被很好地记录下来，但我们努力使图像更清晰，并解决更小尺度的特征，这将有助于详细了解内部环流如何驱动构造板块的运动，反之亦然，并更好地了解热量如何从内部深处输送到表面，这不仅导致了海洋中脊的火山系统，也导致了被称为“热点”的板块中间火山，如夏威夷链。由于比平均温度高的区域对应于低地震速度，这特别难以成像，直到最近，随着精确计算地震波场在地幔上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的工作基础上，利用这种计算来开发整个地幔的全球地震图像，并提高这些图像的清晰度。该项目的主要目标是完成基于时域波形反演方法的更高分辨率（横向可达200-400 km）全球三维径向各向异性全地幔剪切速度模型的构建，该方法目前仅应用于上地幔，并取得了良好的成果。这种波形反演方法建立在PI在波形层析成像中使用基于模式的波场计算的20年经验，以及使用长周期基模和泛音波形（周期为60s）和数值波场计算（谱元法）开发的两代全球上地幔剪切速度模型的基础上。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30s，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。该建议的进一步目标是：(1)在整个地幔径向各向异性的横向变化中获得更高的分辨率；(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；(3)收集额外的、更短的窗口（在起始时间后约30mn）波形至20s，以包含更多的P波能量，并进行额外的迭代，以获得下地幔的全球P速度模型。

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.