On the combination of the magnetotelluric and the geomagnetic depthsounding method for resolving an electrical conductivity increase at 400 km depth

摘要: The simultaneous use of two different passive electromagnetic (EM) sounding techniques for resolving the upper mantle electrical conductivity structure is emphasized: geomagnetic (GM) method uses magnetic field variations at periods between 3 hours and 600 hours, yielding penetration depths 300 km 1000 km. magnetotelluric (MT) applied to a few seconds 16 yields This an extension both methods, using additional D[sub St]-data MT S[sub q]-data GM. In application data from Western Europe resulting overlap target includes increase 10[sup [minus]2] S/m 1 700 depth while single jump either 400, 500 or cannot explain broadband data. Although olivine spinel transition possible explanation enhancement 400 depth, another mineralogy could also occur. has not been resolved in other sub-continental profiles lateral heterogeneity probable this range. 27 refs., figs., 2 tabs.