Long-period (30 days-1 year) electromagnetic sounding and the electrical conductivity of the lower mantle beneath Europe

Details Long-period (30 days-1 year) electromagnetic sounding and the electrical conductivity of the lower mantle beneath Europe Long-period (30 days-1 year) electromagnetic sounding and the electrical conductivity of the lower mantle beneath Europe

Jul 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999geoji.138..179o&link_type=abstract

Geophysical Journal International, Volume 138, Issue 1, pp. 179-187.

Astronomy and Astrophysics

Astronomy

31

Electrical Conductivity, Electromagnetic Induction, Geomagnetic Variations, Mantle

Scientific paper

The C-response connects the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic variations and forms the basis for deriving the conductivity-depth profile of the Earth. Time-series of daily mean values at 42 observatories typically with 50 years of data are used to estimate C-responses for periods between 1 month and 1 yr. The Z: Y method is applied, which means that the vertical component is taken locally whereas the horizontal components are used globally by expansion in a series of spherical harmonics. In combination with results from previous analyses, the method yields consistent results for European observatories in the entire period range from a few hours to 1 yr, corresponding to penetration depths between 300 and 1800 km. 1-D conductivity models derived from these results show an increase in conductivity with depth z to about 2 S m^-1 at z=800 km, and almost constant conductivity between z=800 and z=2000 km with values of 3-10 S m^-1, in good agreement with laboratory measurements of mantle material. Below 2000 km the conductivity is poorly resolved. However, the best-fitting models indicate a further increase in conductivity to values between 50 and 150 S m^-1.

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