Deep electrical structure of Cascadia derived from 3D anisotropic inversion of USArray long-period magnetotelluric data

Summary For a long time,geologists believed that the frequent occurrence of earthquakes in the west coast of the United States is closely related to the existence of a north-south Cascadia subduction zone in the deep part of the region. the National Science Foundation EarthScope/USArray program has collected a large amount of long-period magnetotelluric (MT) data in the area. Many geophysicists have studied these data.From the published results, the approximate distribution of the Cascadia subduction zone in the area can be inferred, but they also pointed out that there is significant electrical anisotropy in the deep underground of this area To solve the problem with electrical anisotropy in 3D MT inversions, we propose a 3D MT anisotropic inversion method that considers simultaneously all principal conductivities and rotation angles. After testing on synthetic data (not shown in the abstract), we applied the method to the Long-period MT data collected from the west coast of the United States.We have successfully developed a 3D MT inversion algorithm for anisotropic earth models. The numerical experiments have proved the effectiveness of our inversion method. The anisotropic characteristics in the Cascadia subduction zone are identified from our inversions. Hope that this will help further analyze the earthquake-prone zone.