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，对于理解地球系统起着至关重要的作用：它承载着有关地球自然资源的重要信息，例如关键矿物；它的厚度控制着海拔和地貌演化的一级变化；作为浅层地壳和上覆地幔之间物质交换的通道，岩浆从中上升；其成分和温度具有大陆早期历史的特征，并控制着地温的分布。的分布然而，由于缺乏通过钻探直接进入以及使用穿过地壳深处的地震能量的不足，准确推断其物理特性，特别是其深层部分，一直具有挑战性。另一方面，可以对深部地壳进行系统采样，并对其物理特性（例如厚度）进行大陆尺度的测量。这项研究通过改进传统的地震方法来解决测量深部地壳特性的挑战，从而减少对深部地壳条件的假设的依赖。 .此外，研究人员将纳入新获得的测量结果可提供有关地壳深层的更多信息，这将有助于推断对成分和强度敏感的弹性特性。最后，这些新技术将应用于通过 EarthScope 收集的整个美国大陆的数据。 USArray 旨在阐明美国本土的大陆尺度深层地壳结构。该研究还将向长岛和纽约地区社区学院的学生提供研究机会。与合作NSF资助的EarthBUS项目。研究目标是大陆地壳，特别是中下部，在地球科学中起着至关重要的作用，因为1）其下边界（莫霍面）控制着第一阶地形变化及其演化，2 ）它是浅层地壳和地幔之间物质交换的通道，也是岩浆上升的通道；3）它的成分具有大陆早期历史的特征；4）它的温度控制着地温和地温的分布。该项目旨在更好地绘制美国大陆下方的深层地壳结构（例如莫霍面深度、与深度相关的地震速度和泊松比），但它们表明了热特性和成分特性。准确测量通常具有挑战性，特别令人感兴趣的是深层地壳的泊松比，因为它表明了石英含量的丰度，因此在确定地壳的化学成分和强度方面起着至关重要的作用。在该项目中，将进行分阶段、三个阶段的研究：首先，将开发和测试一种结合两种传统地震成像技术的优点的新方法，以全面解决速度与深度的权衡问题；其次，将开发和测试一种新的方法；地震可观测的瑞利波局部放大将被进一步纳入，以提供泊松比的深度相关信息，最后，这些新技术将应用于来自 EarthScope USArray 的数据，以照亮大陆尺度的深层；利用合成数据对新方法进行的初步测试显示出解决这些挑战的良好迹象，该研究将解决由于不同地震观测数据的权衡和缺乏而导致的深层地壳特性挑战。这项工作将在大陆尺度上准确地绘制出美国邻近的深层地壳结构，这是该研究工作的成果，即大陆下地壳和上地幔的新三维 (3-D) 模型。美国，将加深对深层地质过程的理解；它还提供了泊松比如何随深度变化的见解，增加了一个重要的地震约束，可以潜在地解决大陆的化学成分和强度问题。该奖项是 NSF 的法定使命，并具有通过使用基金会的智力优点和更广泛的影响审查标准进行评估，被认为值得支持。