Coupling strategies in multiparameter geophysical joint inversion

A big potential lies in the quantitative integration of multiple geophysical measurements for what concerns more unique and robust inversion results, complementary sensitivity to geological features and enhanced resolution. The mechanisms that enable such integration typically rely on statistics where the multiphysics parameter values are related to each other through regression functions (rock physics) or through the shape of the parameter spatial distributions (structure). Such coupling operators are jointly minimized with the data misfit to obtain coupled parameter distributions. We explore the application of various coupling mechanisms to synthetic and real data comprising seismic and electromagnetic measurements acquired in complex geological conditions such as salt geology and complex near surface in desert environment. Two types of structure operators, consisting of the standard cross-gradient and a newly introduced summative gradient, together with rock-physics operators are tested and combined for velocity model reconstruction of salt overburden in a marine environment and in a complex near surface case. Results of seismic-EM joint minimization suggest that the summative gradient operator with the introduction of the sign of the gradient correlation provides a strong coupling mechanism that can become advantageous in the presence of noise-affected seismic data. The rock-physics coupling mechanism is extremely strong and its effectiveness depends primarily on the reliability of the rock-physics relation. A Bayesian approach for the rock-physics operator is introduced to balance the related uncertainties and it is successfully tested in a joint minimization scheme. The combined use of rock-physics and structure coupling operators provides the best results in synthetic and real data applications. The use and combination of various regularization operators, as described, provide a formidable toolbox for solving a wide variety of ill-posed and non-unique geophysical inverse problems.