Quasi Three-Dimensional Lithospheric Conductivity Structure of Continental China

Through SINOPROBE programmes, ultra-wide band, high-quality magnetotelluric (MT) data have been acquired across the continental China in the past years. The MT dataset consists of over 4500 broad band and long period MT stations, which provides constraints for the three-dimensional (3D) conductivity structure of continental China with unprecedented resolution. Recent publications on regional structures have shown that the dataset contributes significantly to insights into the deep structure, dynamics, and evolution of the continental China. However, the interpretation of the whole dataset proves to be challenging in practice, as current 3D inversion schemes could not easily handle the huge dataset, let along the ultra-high degrees of freedom from the mesh associate to the data. Unlike other large-scale array datasets in the world, the site spacing of SINOPROBE can range greatly from hundreds of kilometres in the continental "standard nodes" to 3-10 km for regional arrays and profiles spanning the North China, South China and Tibetan plateau. To address this problem, we propose a new quasi three-dimensional MT inversion scheme to determine the multi-scale conductivity structure of continental China. Inspired by airborne electromagnetic inversion methods, we invert the 3D dataset with spatially constrained stochastic inversions based on a series of one-dimensional forward models. Model regularization constraints are designed to propagate laterally and obliquely among the neighbouring stations with the help of tetrahedron discretizations, suppressing the vertical artefacts commonly found in conventional 1D inversions. Our experiment with the continental-scale field data reveals high resolution conductivity structure that is generally consistent with previous regional models from 3D inversions. Our model also reveals interesting new conductive features in the supposedly stable east Tarim and north Sichuan blocks, which may indicate the re-activation of these old cratons.