1D joint inversion of AMT and resistivity data acquired over a graben

Schlumberger and AMT surveys over 2D resistivity structures are often interpreted using 1D automatic inversion. However, the models obtained using such approach have inherent limitations which must be known. Therefore, the study of model limitations and of alternative interpretations is a very important issue. Using synthetic data sets constructed from a relatively complex conductive graben, we examined the advantage of joint inversion over inversion using individual data sets. The data sets consist of apparent resistivity curves generated by arrays extended parallel and perpendicular to strike. In this case the AMT survey appears to have an advantage over the resistivity survey, since the de data are more affected by lateral effects. As might be expected, neither of the methods is effective in resolving deep structures, located beneath the conductive target, when applied separately. The use of a 1D joint inversion of the data yields a better estimate imaging of the true resistivity distribution. 1D joint inversion of the averaged AMT and de apparent resistivity curves, seems to be the most effective method to determine the resistivity structure. Some of the conclusions derived from the synthetic example are used as guidelines in the interpretation of real field data acquired over a graben, northern Portugal. (C) 1997 Elsevier Science B.V.