5. Joint Inversion of Seismic and MT Data – An Example from Southern Granulite Terrain, India

Inherent ambiguity in the estimations of the subsurface structure made using single geophysical method is well recognized. Use of more than one method to map the same area greatly reduces the ambiguity. Recognizing this fact, there is an increasing trend for the application of multiple geophysical methods and integration of results to develop more confidence on the interpreted model. An earlier study based on integrated geophysical data along the Kuppam- Palani geo-transect in the Southern Granulite Terrain (SGT) revealed a four-layered crustal structure with a seismic low velocity, electrically conducting mid-crustal layer (LVCL). Reliable estimates of LVCL parameters are often difficult to achieve because of equivalence problem. We apply previously developed 1-D joint inversion algorithm to a segment of this transect to analyze the efficacy of the algorithm in reducing the ambiguity in the estimates of LVCL parameters. We take seismic refraction and reflection data corresponding to one shot point, and coincident magnetotelluric data at one location from the part of the profile where the crustal structure is interpreted as layered. Inversion with a large number of initial guesses and model appraisal indicates that LVCL parameters are better constrained with joint inversion than with individual inversions.