Accurately mapping the seismic structure of the deep crust of the continental United States

准确绘制美国大陆深部地壳的地震结构图

• 批准号: 2322632
• 负责人: Weisen Shen
• 金额: $ 31.36万
• 依托单位: SUNY at Stony Brook
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-08-01 至 2026-07-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2322632&HistoricalAwards=false
• 关键词: Accurately; mapping; seismic; structure; deep

Continental crust, the outermost layer of the solid Earth, plays a vital role in understanding the Earth system: it bears important information about the Earth’s natural resources, such as critical minerals; its thickness controls the first order changes in elevation and landscape evolution; it serves as a pathway for material exchange between the shallow crust and overlying mantle, and where magma rises through; its composition and temperature bear the signature of the early history of continents and controls the distributions of the geotherms. Finally, its strength and dynamics dominate the distributions of natural hazards such as earthquakes. However, accurately inferring its physical properties, especially for its deep part, has been challenging due to the lack of direct access through drilling and insufficient indirect sampling. Using seismic energies that travel through the deep crust, on the other hand, can provide systematic sampling to the deep crust and allow a continental-scale measurement of its physical properties such as thickness. This research addresses challenges in measuring the deep crustal properties by improving traditional seismic methods so they rely less on assumptions about deep crustal conditions. Additionally, the researcher will incorporate newly obtained measurements to provide further information about the deeper part of the crust, which will help infer the elastic properties that are sensitive to the composition and strength. Finally, these novel techniques will be applied to data collected throughout the continental United States through the EarthScope USArray to illuminate the continental-scale deep crustal structure of the contiguous US. The research will support a graduate student. Research opportunities will also open to students from community colleges in the Long Island and NYC area. Additional K-12 outreach will be performed by collaborating with the NSF-funded EarthBUS project.The research target, the continental crust, especially the mid- and lower parts, plays a crucial role in Earth Sciences as 1) its lower boundary (Moho) controls the 1st order of topographic variation and its evolution, 2) it serves as a pathway for material exchange between the shallow crust and mantle, and where magma rises through; 3) its composition bears the signature of the early history of continents; and 4) its temperature controls the distributions of the geotherm and surface heat flux. The project aims to better map out the deep crustal structures beneath the continental US. Elastic properties of the deep crust (e.g., Moho depth, depth-dependent seismic velocity, and Poisson’s ratio) indicate the thermal and compositional properties but are often challenging to measure accurately. Of particular interest is the Poisson’s ratio of the deep crust, as it is indicative of the abundance of quartz content, and thus plays a crucial role in determining the chemical composition and strength of the crust. In this project, a phased, 3-stage research will be conducted: First, a novel method that combines the strengths of two traditional seismic imaging techniques to solve the velocity-depth trade-offs comprehensively will be developed and tested; Secondly, a new seismic observable, Rayleigh wave local amplification, will be further incorporated to provide depth-dependent information of the Poisson’s ratio; Finally, these novel techniques will be applied to data from the EarthScope USArray, to illuminate the continental-scale deep crustal structure of the continental US. Preliminary tests of the new methods with synthetic data present a promising sign of solving the challenges. The research will address challenges in measuring the deep crustal properties due to the trade-offs in different seismic observables and a lack of data sensitivity. This work will accurately map out the contiguous US's deep crustal structure at a continental scale. The product of the research work, a new three dimensional (3-D) model of the crust and uppermost mantle beneath the continental US, will deepen the understanding of deep geological processes; It also provides insights into how Poisson’s ratio varies with depth, adding an important seismic constraint that can potentially solve for the chemical composition and strength of the continents.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.

大陆地壳是固体地球的最外层，在理解地球系统中起着至关重要的作用：它具有有关地球自然资源的重要信息，例如关键的稀有性；它的厚度控制着海拔和景观演变的一阶变化；它是在浅层地壳和上覆的地幔之间以及岩浆升起的地方交换物质的途径；它的组成和温度具有大陆早期历史的特征，并控制地理的分布。最后，它的力量和动态主导着自然危害（例如地震）的分布。但是，由于缺乏通过钻井和间接抽样不足的直接访问，因此，准确推断其物理特性，尤其是在其深处，受到了挑战。另一方面，使用穿过深层外壳的地震能可以为深层外壳提供系统的采样，并允许大陆规模的测量构成其物理特性（例如厚度）。这项研究通过改进传统的地震方法来衡量深层地壳特性的挑战，从而减少了对深层地壳条件的假设。此外，研究人员将结合新获得的测量值，以提供有关地壳更深部分的进一步信息，这将有助于推断对组成和强度敏感的弹性特性。最后，这些新型技术将应用于在整个地球上收集的数据，以阐明连续美国的连续尺度深层地壳结构。研究机会也将向来自长岛和纽约市社区大学的学生开放。 Additional K-12 outreach will be performed by collaborating with the NSF-funded EarthBUS project.The research target, the continuous crust, especially the mid- and lower parts, plays a crucial role in Earth Sciences as 1) its lower boundary (Moho) controls the 1st order of topographic variation and its evolution, 2) it serves as a pathway for material exchange between the shallow crust and mantle, and where magma rises through; 3）其组成带有延续早期历史的签名； 4）其温度控制地热和表面热通量的分布。该项目旨在更好地绘制出连续我们下方的深层地壳结构。深层地壳（例如Moho深度，深度依赖性地震速度和Poisson的比例）的弹性特性表示热和复合特性，但通常受到挑战以准确测量。特别令人感兴趣的是泊松的深层托架比，因为它表明了石英含量的抽象，因此在确定地壳的化学组成和强度方面起着至关重要的作用。在这个项目中，将进行一项分阶段的三阶段研究：首先，一种新颖的方法，结合了两种传统的地震成像技术的优势，以全面地解决速度深度折衷，并将经过全面的开发和测试；其次，将进一步纳入可观察到的新的可观察的雷利浪潮局部放大，以提供泊松比的深度依赖性信息。最后，这些新颖的技术将应用于Earthscope UsArray的数据，以阐明连续tal的连续尺度的深层地壳结构。与合成数据的新方法的初步测试提出了解决挑战的希望。这项研究将解决由于不同地震可观察到的折衷和缺乏数据敏感性的权衡而导致的深层地壳特性的挑战。这项工作将以连续的比例准确地绘制出连续的美国深层结构。研究工作的产物是地壳和最高地幔的新的三维（3-D）模型，将加深对深层地质过程的理解。它还提供了有关Poisson比率如何随深度变化的见解，增加了一个重要的地震约束，可以潜在地解决连续性的化学成分和强度。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估审查审查标准来通过评估来获得支持的。