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On the combination of the magnetotelluric and the geomagnetic depthsounding method for resolving an electrical conductivity increase at 400 km depth
Author(s) -
Bahr Karsten,
Olsen Nils,
Shankland Thomas J.
Publication year - 1993
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/93gl02134
Subject(s) - magnetotellurics , geology , earth's magnetic field , geophysics , depth sounding , electrical resistivity and conductivity , conductivity , mineralogy , magnetic field , oceanography , physics , chemistry , quantum mechanics , electrical engineering , engineering
The simultaneous use of two different passive electromagnetic (EM) sounding techniques for resolving the upper mantle electrical conductivity structure is emphasized: The geomagnetic (GM) method uses magnetic field variations at periods between 3 hours and 600 hours, yielding penetration depths between 300 km and 1000 km. The magnetotelluric (MT) method is applied to field variations at periods between a few seconds and 16 hours and yields penetration depths between a few km and 600 km. This is an extension of both methods, using additional D St ‐data for MT and additional S q ‐data for GM. In application to field data from Western Europe the resulting overlap of the target depths includes an electrical conductivity increase from 10 −2 S/m at 300 km to 1 S/m at 700 km depth while a single conductivity jump at either 400, 500 or 700 km cannot explain the broadband data. Although the olivine to spinel transition is a possible explanation of the conductivity enhancement at 400 km depth, another mineralogy could also occur. This conductivity increase has not been resolved in other sub‐continental profiles and lateral heterogeneity is probable in this depth range.