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Abstract:
Detailed mapping of the Earth's magnetic field brings key constraints on the composition, dynamics, and history of the crust. Satellite and near-surface measurements detect different length scales and are complementary. We build a CHAMP and Swarm satellite dataset and combine it with the second version of the World Magnetic Anomaly Map; the most globally complete grid of airborne and marine data. We then derive a lithospheric magnetic field model to SH degree 1300. This step follows a regional approach for modelling the vector, scalar and gradient datasets and allows us to bypass severe numerical issues arising in SH at these high spatial resolutions. In this procedure we perform a series of regional linear inverse problems using robust inversion procedures by parallelization, deal regionally with the Backus effect in equatorial regions, and assess independently each regional model. The initial protocol described in Thébault et al. "A Spherical Harmonic Model of Earth's Lithospheric Magnetic Field up to Degree 1050." Geophysical Research Letters 48.21 (2021): e2021GL095147) was updated for this study. We then estimate a global magnetic crustal thickness using the SH model. Our strategy differs considerably from previous studies in which large spatial scales down to about 2500 km are constrained entirely by global Moho depth models. Here, we process the SH lithospheric magnetic field model in both the spectral and the geographical domains without seismic a priori information. Preliminary results confirm that statistically the Moho depth is indeed a magnetic boundary for the large magnetic spatial scales.
