Home – Home – Jornals – Russian Geology and Geophysics 2010 number 6

A numerical experiment has been applied to explore the potentialities and the limitations of the inversion of IP-affected TEM responses of a two-layer earth with a polarizable layer above (Model 1) or below (Model 2) a nonpolarizable layer. The IP effects have been incorporated into the models via a Cole-Cole complex frequency-dependent conductivity. One of us computed synthetic in-loop and coincident-loop transient responses with added Gaussian noise, and the other performed single and joint inversion of the two sets of pseudoexperimental data. Model 1 turns out to be advantageous over Model 2 in TEM applications and gives a good fit of the Cole-Cole parameters (chargeability, IP time constant, and exponent) even in the absence of a priori information. In the case of Model 2, the lack of a priori information causes problems as to recognize which layer is polarizable, and the fit of the Cole-Cole parameters is generally worse. The layer thicknesses and resistivities are rather accurate in both groups of models, irrespective of whether a priori information is available. As the upper layer increases in thickness ( H ₁), the fit of its parameters ever improves in both models, while the parameters of the lower layer, on the contrary, contain a greater error. Joint inversion of in-loop and coincident-loop transients improves the fit in most cases.
Relative rms error (σ_rel) does not depend on the upper layer thickness for Model 1 but decreases as H ₁ increases in the case of Model 2. The error in joint inversion is times that in single inversion, which means that additional criteria other than σ_rel may be useful to estimate the inversion quality.