Publication 18

On the identification of a transition zone in electrical conductivity between the lithosphere and asthenosphere: a plea for more precise phase data

Cavaliere, T. And Jones A.G.


The magnetotelluric analytical solutions for an earth containing transitional layers in which the electrical conductivity is a function of depth has been considered previously for certain types of restricted models. However, an analytical formulation for an arbitrary n-layered earth containing both constand conductivity layers and transitional layers has not been published. Herein is presented a general matrix technique for such a problem in which the solution matrix is built up from n-1 layer connection matrices. The solution matrix is extremely sparse for n large and can be solved by O(n) operations rather than the usual O(n^3).
This theory is applied to generate the theoretical surface response of two specific models of the lithosphere and asthenosphere. THe first model has a lithosphere/asthenosphere boundary at 80 km, and is representative of "young" oceanic crust and upper mantle. The other model is representative of a continental crust and upper mantle structure with an asthenosphere below 160 km depth.
For both models, techniques of linear inverse theory are applied to ascertain if a transitional zone between the lithosphere and asthenosphere could be resolved by surface measurements. It is shown that the impedance phase data is far more important for resolving this model parameter than is the apparent resistivity data. Accordingly, the need for more precise phase information is stressed.


J. Geophys., 55, 23-30, 1984.

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Alan G Jones / 10 June 2004 /