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

使用远震和全球相位研究南阿巴拉契亚山脉下方地壳和上地幔反射结构的 Vp/Vs 结构

• 批准号: 1830182
• 负责人: Robert Hawman
• 金额: $ 11.99万
• 依托单位: University of Georgia Research Foundation Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-15 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1830182&HistoricalAwards=false
• 关键词: Vp; Vs; Structure; Crust; Reflection

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.

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）深度的地壳和地幔进行回波探测。 该方法部分改编自石油工业使用的勘探技术。这项工作的结果，当添加到其他研究人员的并行分析中时，将允许构建地下的三维模型。 该模型将帮助我们揭示导致阿巴拉契亚山脉和邻近地形形成的地质事件序列以及在那里发现的矿产资源。 该研究将为从事地球科学事业的研究生提供财政支持和宝贵的技术培训。 该赠款还将为本科生提供宝贵的研究经验，并将支持我们针对 4-6 年级学生正在进行的教育/外展计划。 截至 2017 年 10 月，首席研究员已与 2150 多名中小学生（每次 15-20 人一组）进行了板块构造和地震学的户外实践练习。 目前的计划是将这些活动扩展到佐治亚州的更多学区。USArray 穿过美国东部，使人们对大陆岩石圈的精细结构有了全新的认识，并有助于重新激发人们对大陆岩石圈的兴趣。老山带。 拟议的工作将结合使用体波（Ps、SsPmp、PpPmp. 和 PKIKP/PKiKP 生成的反射）来增强 SESAME 阵列站下方阿巴拉契亚山脉南部部分地区的地壳和上地幔图像。 这项工作的目标是解决以下问题：1）能否对大西洋沿岸平原的平均地壳 Vp/Vs 进行更可靠的估计，其中极低速沉积物内的混响往往会压倒莫霍面的 Ps 转换，以及这些 Vp/Vs 值告诉我们在中生代裂谷期间这个高度延伸区域的基底被镁铁质侵入改变的程度？ 2）可用于区分岩石圈和软流圈的小波长反射织物是否存在根本差异？ 3）岩石圈中的应变是否以分布剪切的形式出现，或者通常集中在明确的剪切带上？ 4）我们能否区分地幔中的不同流动模式 - 例如，垂直与水平流动，如果可以，我们能否提高 SKS/PKS/SKKS 到达的垂直分辨率，以对负责观测的深度范围施加更强的限制剪切波分裂？通过首先使用 SsPmp 和 PpPmp 到达构建地壳厚度和平均地壳 P 波速度的局部模型，将获得改进的 Vp/Vs 估计。由此产生的地壳厚度和平均地壳 P 波速度的局部估计集将用于帮助限制对部署在沿海平原的站的 Vp/Vs 的网格搜索。对于上地幔，我们将使用全球地震相位 PKIKP (PKPdf) 作为虚拟源来构建法向入射反射剖面，该剖面类似于地壳主动源反射剖面产生的剖面。该奖项反映了 NSF 的法定使命和通过使用基金会的智力价值和更广泛的影响审查标准进行评估，该项目被认为值得支持。

项目成果

P ‐Wave Reflectivity of the Crust and Upper Mantle Beneath the Southern Appalachians and Atlantic Coastal Plain Using Global Phases

P — 使用全球相位的南阿巴拉契亚山脉和大西洋沿岸平原下方的地壳和上地幔的波反射率

• DOI: 10.1029/2020gl089648
• 发表时间: 2020-09
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Verellen, Devon N.;Alberts, Erik C.;Larramendi, Gustavo A.;Parker, Jr, E. Horry;Hawman, Robert B.
• 通讯作者: Hawman, Robert B.