1. Global crustal models for magnetic applications
Wolfgang Szwillus1, Jörg Ebbing1 Foteini Vervelidou2
1 Institut für Geowissenschaften, CAU Kiel
2 GFZ, Potsdam

2. The induced crustal magnetic field
Measured Total field = Core field Induced Crustal field
580 °C
Magnetite
Induced
Magnetization!
Core field

3. The induced crustal magnetic field
Affected by
Crustal thickness
Crustal composition (controls susceptibility)
Crustal temperature
(Mantle composition, Mantle temperature?)
Challenges
Overwhelmed by the core field in long wavelength
Only short wavelengths of crustal/lithospheric magnetic field are known
Relatively weak link to other geophysical observables

4. Magnetic data fit (magnetic crust)
Forward calculation using tesseroids (Baykiev et al. 2017)
Observed data (MF 400 km height
Moho depth from Crust1.0
Modelled data (Crust1.0) Susc = SI

5. Magnetic data fit (variable susceptibility)
Observed data MF 7
Susceptibility distribution from Hemant and Maus
Modelled data (Variable susceptibility)

6. From thermal modeling to the magnetic field
Heatflow
Crustal thickness
Lithosphere thickness
Ocean floor age
1. Construct a global thermal model
2. Estimate Curie depth
Assume Curie temperature of 580 °C
(Magnetite)
Susceptibility
3. Calculate magnetic field at satellite height
Inducing field (IGRF 12)

7. Thickness of magnetic lithosphere
Assume exponentially decaying heat production
Characteristic depth 10 km
Surface heat productivity −6 W m 3
Positive values indicate (possibly) magnetic mantle
Negative values indicate where the Curie isotherm lies within the crust
Forward calculate magnetic field
With and without mantle magnetization

8. Magnetic data fit (with thermal effect)
Observed data MF 7
Modelled data with Curie depth from thermal model
Constant susceptibility
Crust = SI

9. Spectrum All models lack signal power
Hemant and Maus model (variable susceptibility) comes closest

10. Role of the mantle
Extensive areas are cold enough to allow magnetization
Additional sources in the mantle (i.e. mantle magnetization) helpful?
Thickness of magnetic lithosphere
Modelled magnetic field response of the cold mantle parts

11. Spectral view Small susceptibilities have no noticeable effect
Extremely high mantle susceptibility SI increases power level in SH degree 20-40

12. USGS database (GSC)
Points in GSC database by year of data acquisition

13. Interpolation Use local universal kriging Interpolate on 1 degree grid
Local linear trend estimation
Separate oceanic and continental domains
Interpolate on 1 degree grid
Gives
interpolated values
estimated errors
estimated error covariances

14. Moho depths from local kriging
Estimated uncertainty

15. Impact of different crustal model on magnetic field
By F. Vervelidou

16. The magnetic field in perspective
Crustal composition
Seismology
Crustal thickness
Gravity modelling
Crustal induced magnetic field
Thermal field
Thermal modelling
Employ magnetic field in multi-observable approach!