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Chapter 16. Seismic and Electromagnetic Inversion: Occam’s inversion: A practical algorithm for generating smooth models from electromagnetic sounding data

By
Steven C. Constable
Steven C. Constable
*Scripps Institution of Oceanography, University of California at San Diego, Mail Code A030, La Jolla, CA 92093.
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Robert L. Parker
Robert L. Parker
*Scripps Institution of Oceanography, University of California at San Diego, Mail Code A030, La Jolla, CA 92093.
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Catherine G. Constable
Catherine G. Constable
*Scripps Institution of Oceanography, University of California at San Diego, Mail Code A030, La Jolla, CA 92093.
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Published:
January 01, 2010

Abstract

The inversion of electromagnetic sounding data does not yield a unique solution, but inevitably a single model to interpret the observations is sought. We recommend that this model be as simple, or smooth, as possible, in order to reduce the temptation to overinterpret the data and to eliminate arbitrary discontinuities in simple layered models.

To obtain smooth models, the nonlinear forward problem is linearized about a starting model in the usual way, but it is then solved explicitly for the desired model rather than for a model correction. By parameterizing the model in terms of its first or second derivative with depth, the minimum norm solution yields the smoothest possible model.

Rather than fitting the experimental data as well as possible (which maximizes the roughness of the model), the smoothest model which fits the data to within an expected tolerance is sought. A practical scheme is developed which optimizes the step size at each iteration and retains the computational efficiency of layered models, resulting in a stable and rapidly convergent algorithm. The inversion of both magnetotelluric and Schlumberger sounding field data, and a joint magnetotelluric-resistivity inversion, demonstrate the method and show it to have practical application.

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Contents

Geophysical References Series

Geophysics Today: A Survey of the Field as the Journal Celebrates its 75th Anniversary

Sergey Fomel
Sergey Fomel
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Society of Exploration Geophysicists
Volume
16
ISBN electronic:
9781560802273
Publication date:
January 01, 2010

GeoRef

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