A magnetotelluric survey across the Narmoda-Son lineament along Khandwa-Indore traverse, Madhya Pradesh, Central India

Abstract

A magnetotelluric (MT) survey was conducted across the Narmoda-Son lineament to delineate zones of weakness along the Khandwa-Indore traverse, Madhya Pradesh, Central India. This survey was taken after two strong earthquakes at Jabalpur and Pandhana, of magnitudes 6.4 and 6.0, came in quick succession. One 100 km long profile from Borgaon to Barwaha was chosen, with a station spacing of about 8 to 10 km. MT signals were recorded, within the period range from 0.25 seconds to 4096 seconds, with a Metronix MMS 02E system. These MT signals are capable of mapping the variation in electrical conductivity of the subsurface to a depth of 200 km. A two-dimensional Rapid Relaxation Inversion (RRI) algorithm was used for modelling. Rotational invariant pairs, viz. (rD, fD), (rB, fB) and (rC, fC), and transverse electric (TE) and transverse magnetic (TM) mode pairs (rTE, fTE), (rTM, fTM) were used to generate 2D models. Combined qualitative and quantitative interpretations are highlighted. A highly conducting body is present in the lower crust and uppermost mantle, and it is present in all five models. These conducting rocks in the lower crust and the uppermost mantle may be responsible for the high heat flow in this study area. Rifting of the continent is a prominent signature in all these models. Sharp changes in electrical conductivity at a depth of about 110 to 120 km may be the signature of the lithosphere-asthenosphere boundary. Two-dimensional models generated from the rotation-invariant parameters show broadly the same important features as depicted by TE and TM mode models. Rotation-invariant phases (fD, fB, fC) and apparent resistivities (rD, rB, rC) show the major zones of weakness along the traverse. Pandhana, the location of the epicentre of one recent earthquake in central India, is right over one of the zones of weakness. Static shifts can be used to locate fractures, fissures, and lineaments.