In light of many geophysical imaging results, the regional-scale heterogeneity is naturally decreased with depth, and the heterogeneity in the depths of <200 km is fundamentally an ubiquitous feature 9. The effective viscosity of the lithospheric mantle depends on the composition, differential stress, ambient temperature and pressure, water and its fugacity, the grain sizes of minerals, and so on. In multi-scale geodynamic modeling 1, 2, 3, the investigation of fine-scale deformation in the lithosphere 4, 5 and interpretation of large-scale geophysical data 6, 7, 8, the spatial variation of effective viscosity plays a key role. We briefly discussed the potentials and associated problems for application. The results show that the effective viscosity structure coincides well with that estimated from other independent datasets at depths of 40 to 80 km but differs slightly at depths of 100 to 200 km. We then apply the method to transform an electrical conductivity cross-section across the Yangtze block and the North China Craton. The proposed transform is robust and has been verified by application to data synthesized from an intraoceanic subduction zone model. The contribution of water content to the effective viscosity is isolated in a flow law with reference to relatively dry conditions in the upper mantle. Here, we build a relationship between effective viscosity and electrical conductivity in the upper mantle using water content. Recently, a promising estimation of effective viscosity was obtained from a transform derived from the results of magnetotelluric imaging. At present, an effective method to obtain a high-resolution viscosity structure is still lacking.
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