Probing 3-D electrical conductivity of the mantle using 6 years of Swarm, CryoSat-2 and observatory magnetic data and exploiting matrix Q-responses approach

Alexey Kuvshinov,Nils Olsen,Lars Tøffner-Clausen,Alexander Grayver

doi:10.1186/s40623-020-01341-9

Alexey Kuvshinov, Nils Olsen + Show 2 more

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https://doi.org/10.1186/s40623-020-01341-9

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Abstract

This study presents results of mapping three-dimensional (3-D) variations of the electrical conductivity in depths ranging from 400 to 1200 km using 6 years of magnetic data from the Swarm and CryoSat-2 satellites as well as from ground observatories. The approach involves the 3-D inversion of matrix Q-responses (transfer functions) that relate spherical harmonic coefficients of external (inducing) and internal (induced) origin of the magnetic potential. Transfer functions were estimated from geomagnetic field variations at periods ranging from 2 to 40 days. We study the effect of different combinations of input data sets on the transfer functions. We also present a new global 1-D conductivity profile based on a joint analysis of satellite tidal signals and global magnetospheric Q-responses.

Highlights

Understanding 3-D physical properties of the Earth’s mantle on a global scale is an outstanding problem of modern geophysics
Seismic tomography provides a variety of global 3-D velocity models (Debayle and Ricard 2012; Lekic and Romanovicz 2011; Ritsema et al 2011; Schaeffer and Lebedev 2013, among others), but the interpretation of seismic velocities alone leads to ambiguities
Until now Geomagnetic Depth Sounding (GDS) studies most often rely on the long-period variations of magnetic field of magnetospheric origin coming from a global network of geomagnetic observatories

Summary

Introduction

Understanding 3-D physical properties of the Earth’s mantle on a global scale is an outstanding problem of modern geophysics. Since the conductivity is sensitive to temperature, chemical composition and hydrogen content (Karato and Wang 2013; Khan 2016; Yoshino 2010, among others) its knowledge helps understanding the Earth’s origin as well as its past evolution and recent dynamics. Until now GDS studies most often rely on the long-period variations of magnetic field of magnetospheric origin coming from a global network of geomagnetic observatories. From these data local C-responses (Banks 1969) (see Appendix A of this paper explaining the concept) are estimated at a number of periods and inverted for mantle conductivity. There are numerous studies (Chen et al 2020; Khan et al 2011; Munch et al 2018; Schultz and Larsen 1990; Zhang et al 2020, among others) that performed 1-D inversions of local C-responses at a number of locations in order to detect lateral variations in the mantle conductivity

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