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

北美大陆是在数十亿年的时间里通过大陆碎片的碰撞和较大大陆的分裂而形成的。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这段历史。该项目的目的是将这种能力扩展到地球表面以下。虽然埋藏的岩石无法直接看到和绘制，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，在它们所穿过的岩石上留下了信息。我们将绘制的地表岩石变形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，这些信息可用于绘制地壳变形的地图。 该项目使我们能够读取地表下过去地质过程的记录，从而增进地球科学知识。由于当前的地质过程也会使岩石变形，因此该方法还可用于绘制地震断层的根源图，这对于估计地震危险性很有用。在此过程中研究的岩石特征也与地质资源测绘相关。此外，准确了解地震信号上岩石结构的印记使我们能够避免地震数据其他用途的偏差，例如自然和人造地震源的定位和表征。EarthScope 计划的既定目标是导出对大陆变形历史的约束。该项目旨在弥合实验室测量的微观结构岩石结构、映射到露头暴露位置的变形结构以及在公里级地震波长下引起地震各向异性的岩石结构的尺度。项目组成部分包括：1) 整合来自多种技术和地震网络的地震各向异性观测；2) 将包含叶理、线理和映射的主要延性断层和脆性断层的现有数字结构数据集贡献到现有的 EarthCube 资助和美国地质调查局持有的数据库中，以及从约 1:100,000 比例图到手工样本计算体弹性张量；以及 3) 使用简单的方法对从 EarthCube 资助的数据库中提取的地震观测和结构数据进行合成和联合解释相关性以及从代表岩石类型的弹性张量到地质叶理图再到地震波长尺度各向异性的显式标度。将地壳地震各向异性与地壳应变历史联系起来的能力需要1）地壳岩石弹性特性的代表性目录以及它们如何在地震波长尺度上平均；2）主要结构参数的汇编，例如变质岩和火成岩中主要岩石结构（叶理和线理）的方向及其内部相干性独特的域，以及断层带等更离散特征的方向，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的汇编，并使其在网上广泛提供。

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.