Global maps of the magnetic thickness and magnetization of the Earth’s lithosphere

Foteini Vervelidou,Erwan Thébault

doi:10.1186/s40623-015-0329-5

Abstract

We have constructed global maps of the large-scale magnetic thickness and magnetization of Earth’s lithosphere. Deriving such large-scale maps based on lithospheric magnetic field measurements faces the challenge of the masking effect of the core field. In this study, the maps were obtained through analyses in the spectral domain by means of a new regional spatial power spectrum based on the Revised Spherical Cap Harmonic Analysis (R-SCHA) formalism. A series of regional spectral analyses were conducted covering the entire Earth. The R-SCHA surface power spectrum for each region was estimated using the NGDC-720 spherical harmonic (SH) model of the lithospheric magnetic field, which is based on satellite, aeromagnetic, and marine measurements. These observational regional spectra were fitted to a recently proposed statistical expression of the power spectrum of Earth’s lithospheric magnetic field, whose free parameters include the thickness and magnetization of the magnetic sources. The resulting global magnetic thickness map is compared to other crustal and magnetic thickness maps based upon different geophysical data. We conclude that the large-scale magnetic thickness of the lithosphere is on average confined to a layer that does not exceed the Moho.

Highlights

The magnetic field on the Earth’s surface results from the superposition of various sources, both of internal and external to the Earth origin
In section “Surface spherical cap harmonic power spectrum”, we use the Revised Spherical Cap Harmonic Analysis (R-SCHA) methodology (Thébault et al 2004, 2006, Thébault 2008) and derive an expression for the surface spherical cap harmonic power spectrum, which we show can be directly related to any spherical harmonic (SH) power spectrum
Considering that lithospheric magnetic field data and models do not include larger wavelength due to the masking by the core field, this cut-off value is sufficient to minimize the values of the mean magnetic field

Summary

Introduction

The magnetic field on the Earth’s surface results from the superposition of various sources, both of internal and external to the Earth origin. As a consequence of the dominant role of the core field, the large-scale lithospheric magnetic field corresponding. New ways of recovering Earth’s large-scale magnetic thickness and magnetization, that do not rely on the assumption that Moho is a magnetic boundary, would provide some independent assessment. This in turn could contribute to studies on the composition and the thermal state of Earth’s lithosphere (e.g., Fox Maule et al 2005), since the minerals are only magnetized down to the Curie isotherm

Methods

Results

Discussion

Conclusion