Building a continent: Integration of surface geology, rock physics, and seismic observations to investigate the tectonic history of the contiguous United States

北美大陆经过数十亿年的时间，通过大陆碎片的碰撞和较大大陆的裂解而形成。地质学家可以通过观察暴露在地球表面的过去变形的岩石来解读其中的一些历史。该项目的目标是将这种能力扩展到地球表面以下。虽然埋藏的岩石不能直接看到和绘制地图，但它们不断被世界各地地震的地震波穿过。这些波在到达地球表面之前，会在它们通过的岩石上留下信息。我们将绘制的地表岩石变形图与地下地震信息相结合，以找出如何从地震数据中提取印记信息。然后，这些信息可以用来绘制地壳是如何变形的。该项目通过允许我们阅读地表下过去地质过程的记录，促进了对地球科学的了解。由于目前的地质过程也会使岩石变形，这种方法还可以用来绘制地震发震断层的根部图，这对地震危险性的估计很有用。在这一过程中调查的岩石特征也与地质资源填图有关。此外，对地震信号上岩石组构印记的准确了解使我们能够避免在地震数据的其他用途中产生偏差，例如用于自然和人造震源的定位和表征。EarthScope计划的一个明确目标是得出大陆变形历史的约束。该项目旨在从实验室测量的微结构岩石组构，到露头暴露测绘的变形结构，以及在千米级地震波长上造成地震各向异性的岩石组构之间架起桥梁。项目的组成部分是1)来自多种技术和地震台网的地震各向异性观测的集成，2)现有数字构造数据集的贡献，包括叶理、线理、并将主要的韧性和脆性断层绘制到现有的EarthCube资助的数据库和美国地质调查局持有的数据库中，以及从~1：100,000比例的地图到手持样本的整体弹性张量的计算，以及3)使用直接的相关性以及从代表岩石类型的弹性张量到地质面理图再到地震波长尺度各向异性的显式缩放来合成和联合解释从EarthCube资助的数据库提取的地震观测和结构数据。要将地壳地震各向异性与地壳的应变历史联系起来，需要1)地壳岩石的弹性属性及其在地震波长尺度上的平均情况的代表性目录以及2)主要构造参数的汇编，例如变质岩和火成岩中主要岩石组构(面理和线理)的取向及其在独特区域中的内部一致性，以及更多离散特征的方向，如断裂带，以便能够与地震测量的各向异性进行定量比较。拟议的工作将集中现有汇编，并在网上广泛提供。

The North American continent formed over billions of years via the collision of continental fragments and the rifting apart of larger continents. Geologists can read some of this history by looking at rocks exposed at the Earth's surface that were deformed in the past. The aim of this project is to extend this ability below the Earth's surface. While buried rocks cannot be seen and mapped directly, they are constantly traversed by seismic waves from earthquakes around the world. These waves are imprinted with information on the rocks they travel through before reaching the Earth's surface. We combine mapped rock deformation at the surface with seismic information from the subsurface in order to find out how to extract the imprinted information from the seismic data. The information can then be used to map how the Earth's crust was deformed. The project advances knowledge of Earth science by allowing us to read the record of past geological processes beneath the surface. Because current geological processes also deform rocks, the method can also be used to map the roots of earthquake-generating faults, which is useful for estimates of seismic hazard. The rock characteristics investigated in this process are also relevant to mapping geological resources. Additionally, accurate knowledge of the imprint of rock fabrics on the seismic signal enables us to avoid biases in other uses of the seismic data, such as for location and characterization of natural and human-made seismic sources.A stated goal of the EarthScope program is to derive constraints on the deformation history of the continent. This project aims to bridge the scales from microstructural rock fabrics measured in the laboratory, to deformation structures mapped on outcrop exposures, and to rock fabrics causing seismic anisotropy at km-scale seismic wavelengths. Project components are 1) integration of seismic anisotropy observations from multiple techniques and seismic networks, 2) contribution of existing digital structural data sets containing foliations, lineations, and mapped major ductile and brittle faults to existing EarthCube-funded and U. S. Geological Survey-held databases as well as calculation of bulk elasticity tensors from ~1:100,000 scale maps to hand samples and 3) synthesis and joint interpretation of seismic observations and structural data extracted from EarthCube-funded databases using straightforward correlations as well as an explicit scaling from elastic tensors representative of rock types to geological foliation maps to seismic wavelength-scale anisotropy.The ability to relate crustal seismic anisotropy to the strain history of the crust requires 1) a representative catalog of elastic properties of crustal rocks and how they average at scales of seismic wavelengths and 2) a compilation of major structural parameters such as orientations of dominant rock fabrics (foliation and lineation) in metamorphic and igneous rocks and their internal coherence in unique domains, as well as orientations of more discrete features such as fault zones, in order to enable quantitative comparisons to anisotropy measured seismically. The proposed work will centralize existing compilations and make them widely available online.