Collaborative Research: Integration of USArray Magnetotelluric and Seismic Data in the Pacific Northwest

在这个项目中，我们结合了地球内部成像的两种地球物理方法（地震和电磁），以提高我们对美国西北太平洋地区地质历史和地球当前结构的理解。这些研究将提高我们对该地区非常动态的地球的理解，提供最终有助于减轻地震和火山爆发等地质灾害的信息，并为开发自然资源（如地热能）的努力提供信息。该项目的核心数据集由nsf资助的Earthscope可移动阵列提供，该阵列提供高质量地震和电磁（EM）站点的空间统一网格。从地震和电磁地球镜数据中分别获得的图像进行初步比较，发现惊人的相似性，这表明不同但似乎相关的材料特性具有共同的大规模几何分布。通过这个项目，我们正在开发更复杂的方法来整合这两个数据集，目标是对该地区地球内部的物理状态和组成提供新的限制。预期所开发的方法将更广泛地适用于其他区域对地球结构和地质历史的类似研究，以及联合地球物理成像对资源勘探或环境问题的较小规模应用。地壳和上地幔深处的大块岩石导电性受到即使是少量相互连接的导电相的强烈影响，这使得电磁方法成为绘制流体分布和约束岩浆过程的有力工具。然而，孤立地解释电磁数据往往是模糊的，因为可能有多种原因导致高导电性，而且分辨率本质上受到导体中电磁场扩散性质的限制。通过整合电磁和地震数据，可以减少两者的非唯一性，为地球内部的成分和物理状态提供更强大和有用的约束。关于方法，我们的方法将跨越一个范围，从通过单独反演每种类型的数据获得的“无偏”模型的简单相互比较，通过对共同结构假设的检验，到正式的联合反演。此次合作加强了地震和电磁研究人员之间的联系，并通过对年轻研究人员进行互补的地球物理技术培训，有望在未来几年提高对Earthscope和其他地球物理数据集的解释。

In this project we are combining two geophysical methods for imaging Earth's interior (seismic and electromagnetic) to improve our understanding of the geologic history, and present structure of the Earth in the Pacific Northwest United States. These studies will improve our understanding of the very dynamic Earth in this region, providing information that will ultimately help to mitigate geologic hazards such as earthquakes and volcanic eruptions, and inform efforts to develop natural resources (e.g., geothermal energy). The core dataset for this project is provided by the NSF-funded Earthscope Transportable Array, which provides co-located spatially uniform grids of high quality seismic and electromagnetic (EM) sites. Initial comparison of images obtained from the seismic and EM Earthscope data separately reveal striking similarities, which suggest a common large-scale geometric distribution of different, but plausibly related, material properties. Through this project we are developing more sophisticated methods for integrating the two datasets, with the goal of providing new constraints on physical state and composition of Earth's interior in this region. The methods developed are expected to be more widely applicable, both to similar studies of Earth structure and geologic history in other regions, and for smaller scale applications of joint geophysical imaging to resource exploration or environmental problems.Bulk rock conductivities at crustal and upper mantle depths are strongly influenced by even small amounts of an interconnected conductive phase, making EM methods a powerful tool for mapping fluid distributions and constraining magmatic processes. However, interpretation of EM data in isolation is often ambiguous, as there can be multiple possible causes for high conductivity, and resolution is intrinsically limited by the diffusive nature of EM fields in a conductor. By integrating EM and seismic data non-uniqueness in both can be reduced, providing more powerful and useful constraints on composition and physical state of Earth's interior. With regard to methodology, our approach will span a spectrum, from simple inter-comparison of "unbiased" models obtained by inverting each type of data separately, through testing of hypotheses of common structure, to formal joint inversion. The collaboration is strengthening connections between seismic and EM researchers, and through training of young researchers in complimentary geophysical techniques, promises to enhance future interpretation of Earthscope and other geophysical datasets in the coming years.