Mantle Structures Beneath USArray

地震学的重大挑战之一是在不同板块之下及其边界建立上地幔的三维地震速度场。正是在这些深度，机械强度较强的外部岩石圈层过渡到相对较软的软流层，软流层变形并流动，产生板块运动。旧克拉通之下的大陆岩石圈很冷，似乎缺乏铁等重矿物。因此，它们保持了相对稳定。这项研究的目的是锐化现有的层析图像，为高分辨率的板块运动动态模拟提供基础。随着USArray的出现，研究太平洋海盆向北美克拉通过渡的机会前所未有。这个数据集显示了大量的P和S身体波形的复杂性，这取决于沿海岸山脉和落基山锋的到达方向。这些特征可以用多路径来解释，其中有两条路径到达车站，其中一条沿着相对于慢速路径的快速路径行进。开发了一种多路径探测器(MPD)处理技术来绘制下行板和羽状特征等结构的锐度图。这些构造中的许多都可以在现有的断层图像中看到，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，北美克拉通在本质上看起来相对单一，但具有复杂的垂直分层，至少在上地幔过渡带是这样。在这些上地幔精细结构的模拟结果之后，将进行第二阶段的工作，即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.