Van der Waals-Zeeman Colloquium
Tuesday, 21 Oct 2008, 16:00h
Obtaining linear system responses from recorded field fluctuations
Dr. Evert Slob
Applied geophysics & Petrophysics group, Department Geotechnology, Faculty Civil Engineering and Geosciences, TU Delft.
Starting from the principle of reciprocity, it can be shown that the response, or Green's, function can be retrieved for a wide class of linear systems that are described either by scalar or vector fields. Relevant examples of such systems in exploration geophysics include the pore pressure in reservoirs or aquifers, propagation of electromagnetic and seismic waves, diffusive electromagnetic fields and coupled electromagnetic and elastic wave fields in dissipative porous media (the subsurface). For sources of the field fluctuations that are confined to a closed surface around a lossless medium, the cross correlation of recorded fields at two receivers results in the medium response between these receivers. In contrast, for sources of the field fluctuations that are confined to a closed surface around a dissipative medium, additional sources must be distributed throughout the volume to compensate for the dissipation. For strongly dissipative media we propose multidimensional deconvolution as an alternative that does not require sources throughout the volume. For both methods advantages and disadvantages for practical applications are given and illustrated with examples.