Mantle Structures Beneath USArray

地震学的一个重大挑战是建立不同板块下及其边界上地幔的三维地震速度场。正是在这些深度，机械上强大的外岩石圈层转变为相对柔软的软流层，软流层变形和流动产生板块运动。古克拉通下面的大陆岩石圈很冷，似乎铁等重矿物已经枯竭。因此，它们保持相对稳定。本研究的目的是锐化现有的层析成像图像，为高分辨率的板块运动动态建模提供基础。随着USArray的出现，为研究从太平洋盆地到北美克拉通的转变提供了前所未有的机会。该数据集显示了大量的P和S体波形复杂性，这取决于沿海岸山脉和落基山锋到达的方向。这些特征可以用多路径来解释，即有两条路径到达车站，一条沿着相对于一条慢路径的快速路径行进。一种多路径探测器（MPD）处理技术已经被开发出来，用于绘制出诸如下行板块和羽状特征等结构的清晰度。许多这样的结构可以在现有的层析成像图像中看到，只需要一些锐化就可以产生与这些复杂波形相匹配的合成地震图。相比之下，北美克拉通的性质相对单一，但其垂向分层复杂，至少在上地幔过渡带是如此。这些上地幔精细结构的建模结果之后，将进行第二阶段的努力，为整个地幔构建一个详细的跨太平洋-克拉通走廊。

One of the grand challenges in seismology is to develop a three-dimensional seismic velocity field of the upper-mantle beneath the various plates and at their boundaries. It is at these depths where the mechanically strong outer lithosphere layer transitions into the relatively soft asthenosphere which deforms and flows to produce plate motions. The continental lithosphere beneath old cratons is cold and appears to be depleted in heavy minerals such as iron. Thus, they remain relatively stable. The objective of this study is to sharpen existing tomographic images to provide a basis for high-resolution dynamic modeling of the plate motions. With the advent of USArray, there is an unprecedented opportunity for investigating the transition from the Pacific Basin to the North American Craton. This data set displays a great deal of P and S body waveform complexity depending on direction of arrivals both along the Coastal Ranges and the Rocky Mountain Front. These features can be explained by multi-pathing where there are two paths to reach the station, one traveling along a fast path relative to a slow path. A Multi-Path Detector (MPD) processing technique has been developed to map out the sharpness of structures such as down-going slabs and plume-like features. Many of these structures can be seen in existing tomographic images and only require some sharpening to produce synthetic seismograms matching these complex waveforms. The North American Craton in contrast appears relatively one-dimensional in nature but with complicated vertical layering, at least for the upper-mantle transition zone. These modeling results of the upper-mantle fine structure will be followed by a second stage effort of constructing a detailed Trans-Pacific-Craton corridor for the entire mantle.