Mantle Structures Beneath USArray

USArray 下方的地幔结构

• 批准号: 1053064
• 负责人: Donald Helmberger
• 金额: $ 24.38万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-05-01 至 2015-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1053064&HistoricalAwards=false
• 关键词: Mantle; Structures; Beneath; USArray

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.

地震学的重大挑战之一是建立各板块之下及其边界上地幔的三维地震速度场。正是在这些深度，机械强度较强的岩石圈外层过渡到相对较软的软流圈，软流圈变形并流动，产生板块运动。古老的火山岩之下的大陆岩石圈是寒冷的，似乎缺乏重矿物，如铁。因此，它们保持相对稳定。本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的动态建模提供基础。随着USAray的出现，有一个前所未有的机会，调查从太平洋盆地到北美大陆的过渡。该数据集显示了大量的P和S体波形的复杂性，这取决于到达方向都沿着海岸山脉和落基山脉前。这些特征可以用多路径来解释，其中有两条路径到达站，一条沿着相对于慢路径的快速路径沿着。已经开发了多路径检测器（MPD）处理技术来绘制出结构的锐度，例如下行板和羽状特征。这些结构中的许多结构可以在现有的层析成像图像中看到，并且仅需要一些锐化来产生与这些复杂波形匹配的合成地震图。相比之下，北美的地幔柱在性质上相对一维，但具有复杂的垂直分层，至少在上地幔过渡带是如此。这些上地幔精细结构的模拟结果将随后的第二阶段的努力，构建一个详细的跨太平洋-地幔走廊的整个地幔。