Vp/Vs Structure of the Crust and Reflection Fabric of the Upper Mantle beneath the Southern Appalachians using Teleseismic and Global Phases

这项工作的目的是更好地了解美国东南部从阿巴拉契亚山脉到海岸的深层地质结构。通过使用远距离地震产生的地震波，研究人员能够对300公里(180英里)深的地壳和地幔进行回波探测。该方法在一定程度上借鉴了石油行业使用的勘探技术。这项工作的结果，当添加到其他研究人员的平行分析时，将允许构建地下的三维模型。这个模型将帮助我们解开导致阿巴拉契亚山脉和邻近地形形成的一系列地质事件，以及那里发现的矿产资源。这项研究将为在地球科学领域寻求职业生涯的研究生提供资金支持和宝贵的技术培训。这笔助学金还将为本科生提供宝贵的研究经验，并将支持我们为4-6年级学生正在进行的教育/推广计划。截至2017年10月，首席调查员已与2150多名中小学生(每次15至20人一组)进行了板块构造和地震学的户外动手练习。目前的计划是将这些活动扩展到乔治亚州更多的学区。美国阵列号在美国东部的通过从根本上对大陆岩石圈的精细结构产生了新的见解，并帮助重新点燃了人们对老山带的兴趣。拟议的工作将使用体波(Ps，SsPmp，PpPmp)的组合。和PKIKP/PKiKP产生的反射)，以增强我们对南部阿巴拉契亚山脉部分地区的地壳和上地幔的图像，这些图像位于SESAME阵列的台下。这项工作的目标是解决以下问题：1)能否获得更可靠的跨大西洋海岸平原地壳平均Vp/V的估计，在那里，极低速沉积物中的混响往往超过来自莫霍面的Ps转换，这些Vp/Vs值告诉我们，在中生代裂谷期间，这个高度伸展区域的基底被镁铁质侵入体改变的程度如何？2)可以用来区分岩石圈和软流圈的小波长反射组构是否存在根本差异？3)岩石圈中的应变是以分布剪切的形式发生的，4)我们能否区分地幔中不同的流动模式--例如，垂直流动和水平流动，如果是的话，我们能否提高SKS/PKS/SKKS到达的垂直分辨率，以对观测到的剪切波分裂的深度范围施加更强的约束？通过首先利用SsPmp和PpPmp波到达建立地壳厚度和平均地壳P波速度的本地化模型，将获得更好的Vp/Vs估计。由此得到的一组地壳厚度和平均地壳P波速度的本地化估计将被用来帮助限制在沿海平原部署的台站的Vp/Vs的网格搜索。对于上地幔，我们将使用全球地震震相PKIKP(PKPdf)作为虚拟震源来构建垂直入射反射剖面，这些剖面类似于地壳主动震源反射剖面产生的反射剖面。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The purpose of this work is to gain a better understanding of the deep geologic structure of the southeastern U.S., from the Appalachian Mountains to the coast. By using seismic waves generated by distant earthquakes the investigators are able to conduct echo soundings of the Earth's crust and mantle to a depth of 300 km (180 miles). The methodology is adapted in part from exploration techniques used by the petroleum industry. The results from this work, when added to parallel analyses by other researchers, will allow the construction of a three-dimensional model of the subsurface. This model will help us to unravel the sequence of geologic events that led to the formation of the Appalachian mountains and adjacent terrain and the mineral resources found there. The research will provide financial support and valuable technical training for graduate students pursuing careers in the geosciences. The grant will also provide valuable research experience for undergraduate students and will support our ongoing education/outreach program for students in grades 4-6. As of October 2017, the principal investigator had worked with over 2150 elementary and middle-school students (in groups of 15-20 at a time) in outdoor, hands-on exercises in plate tectonics and seismology. The current plan is to expand those activities to additional school districts across the state of Georgia.The passage of USArray across the eastern United States has resulted in fundamentally new insights into the fine-scale structure of the continental lithosphere and has helped to rekindle interest in old mountain belts. The proposed work will use a combination of body waves (Ps, SsPmp, PpPmp. and reflections generated by PKIKP/PKiKP) to enhance our images of the crust and upper mantle across a portion of the southern Appalachians, beneath stations of the SESAME array. The goal of this work is to address the following questions: 1) Can more reliable estimates of average crustal Vp/Vs be obtained across the Atlantic Coastal Plain, where reverberations within very low-velocity sediments tend to overwhelm Ps conversions from the Moho, and what do those values of Vp/Vs tell us about the degree to which the basement in this highly extended region was modified by mafic intrusions during Mesozoic rifting? 2) Are there fundamental differences in small-wavelength reflection fabric that might be used to distinguish lithosphere from asthenosphere? 3) Does strain in the lithosphere occur as distributed shear, or is it typically localized along well-defined shear zones? 4) Can we distinguish between different flow patterns in the mantle - e.g., vertical versus horizontal flow, and if so, can we improve on the vertical resolving power of SKS/PKS/SKKS arrivals to place stronger constraints on depth ranges responsible for observations of shear-wave splitting? Improved estimates of Vp/Vs will be obtained by first constructing localized models of crustal thickness and average crustal P-wave velocity using SsPmp and PpPmp arrivals. The resulting set of localized estimates of crustal thickness and average crustal P-wave velocity will be used to help constrain the grid search for Vp/Vs for stations deployed in the Coastal Plain. For the upper mantle, we will use the global seismic phase PKIKP (PKPdf) as a virtual source to construct normal-incidence reflection sections that are analogous to those produced by active-source reflection profiling of the crust.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.