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

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Abstract

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).
Original languageEnglish
JournalGeophysical Journal International
Volume138
Issue number1
Pages (from-to)179-187
ISSN0956-540X
Publication statusPublished - 1999

Keywords

  • electrical conductivity
  • mantle
  • geomagnetic variations
  • electromagnetic induction

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