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

在这个项目中，我们结合了两种地球物理方法来成像地球内部（地震和电磁），以提高我们对地质历史的理解，以及美国太平洋西北部地球的当前结构。 这些研究将提高我们对该地区非常动态的地球的了解，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（例如，地热能）。 该项目的核心数据集由NSF资助的Earthscope Transportable Array提供，该阵列提供高质量地震和电磁（EM）站点的空间均匀网格。 从地震和EM Earthscope数据分别获得的图像的初步比较显示惊人的相似性，这表明一个共同的大规模的几何分布不同，但可能相关的材料属性。 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，目的是为该地区地球内部的物理状态和组成提供新的限制。 所开发的方法有望得到更广泛的应用，既可用于其他地区的地球结构和地质历史的类似研究，也可用于资源勘探或环境问题的联合地球物理成像的小规模应用。地壳和上地幔深度的大块岩石电导率受到即使少量的互连导电相的强烈影响，使EM方法成为绘制流体分布图和约束岩浆过程的有力工具。 然而，孤立地解释EM数据通常是模糊的，因为高电导率可能有多种可能的原因，并且分辨率本质上受到导体中EM场的扩散性质的限制。 通过整合EM和地震数据，可以减少两者的非唯一性，从而对地球内部的组成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频谱，从简单的“无偏”模型的相互比较，通过分别反演每种类型的数据，通过测试共同结构的假设，以正式的联合反演。 此次合作加强了地震和EM研究人员之间的联系，并通过对年轻研究人员进行补充地球物理技术的培训，有望在未来几年加强Earthscope和其他地球物理数据集的未来解释。

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.