Constraining the mantle conductivity structure beneath Eurasia by inverting geomagnetic diurnal variation full-term transfer functions

Summary As the world’s largest continental plate, the deep electrical conductivity structure of the Eurasian continent holds great importance for understanding continental evolution and mantle dynamics. Conventional geomagnetic response functions based on magnetospheric ring current have limited sensitivity in constraining the electrical structure of the upper mantle and transition zone (200-500 km). Previous studies utilizing ionospheric Sq signals considered only the dominant-term transfer functions, neglecting information carried by non-dominant term transfer functions. This study proposes a mantle conductivity structure imaging method based on inverting full-term transfer functions. It incorporates trans-dimensional Bayesian inversion to analyze Sq signals from 14 geomagnetic observatories across Eurasia, thereby obtaining one-dimensional electrical structures beneath each observatory. Results reveal large lateral heterogeneity in the mantle conductivity structure across Eurasia, with conductivity discontinuities at 100-200 km depth indicating a lithosphere-asthenosphere boundary (LAB) that progressively deepens from east to west. A distinct conductivity discontinuity at 400-500 km depth beneath eastern Eurasia may result from water transport into the mantle through Western Pacific plate subduction. This research demonstrates the advantage of full-term transfer functions in illuminating mantle conductivity structures, providing new pathways for investigating deep Earth material cycles.