Dimensionality analysis of MT data using Mohr circle: A case study from Rewa–Shahdol region, India

Abstract

Mohr circle in magnetotelluric (MT) is being used to represent dimensionality of subsurface structure. Mohr circle plot on individual axes for each frequency represents the dimensionality concerning frequency, whereas plotting of Mohr circle on common Cartesian coordinates for all frequencies displays the effects of noise on the impedance tensor. Here, we examine the Rewa–Shahdol region MT data with the Mohr circle approach to understand the sub-surface dimensionality structure, but the presence of noise in the signal has randomized the Mohr circle response. Hence, we made an effort to obtain the subsurface dimensionality using Mohr circle properties and derive two new invariants such as tan ϕ and sin θ. The two invariants represent the dimensionality and anisotropy nature of the subsurface structure. Results from the Mohr circle together with the new angles brought out the 1-D graben structure of the Gondwana and Vindhyan basins, 2-D/3-D nature of the underlying basement structure and the crustal structure below the Narmada–Son Lineament (NSL) zone. 2-D/3-D nature of the NSL zone represents the basement uplifted horst structure between Gondwana and Vindhyan basins. Further, the horst-graben structure of NSL zone is evident from the Mohr circle analysis suggesting of rifting and block movement.