Estimation of sediment thickness (including Mesozoic) in the western central part of Kachchh Basin, Gujarat (India) using Magnetotellurics

Abstract

The Magnetotellurics (MT) survey has been conducted along a North-South profile having a length of 55 km with the station spacing of 2–3 km in the western central Kachchh, from Shervo village in the north to Dujapar village in the south for estimation of Mesozoic sediment thickness. A total of 18 MT stations have been acquired. The three different 1D inversion techniques (Occam inversion, Bostick inversion and Least square inversion (ZondMT1D)) have been applied to the data, which reveals three different types of subsurface layer sequences by averaging result from all the methods. In the northern part of the profile, ~1000 m thick Mesozoic sediments with resistivity in the range of 2–15 Ω.m is present beneath the ~700–800 m conductive (from 0.5 Ω.m to 2.0 Ω.m) recent (Quaternary-Tertiary) sediments whereas, in the southern part of the profile ~1500 m thick Mesozoic sediments are inferred to be rested under ~400–500 m thick resistive (from 50 Ω.m to 90 Ω.m) Deccan basalt. The ~1800–2000 m thick Mesozoic sediments are imaged as a shallow conductive layer overlying the resistive crystalline basement rocks in the middle of the profile. The Mesozoic sediment thickness ~1500–2000 m is computed in the study area which correlates well with the lithology from a borehole drilled nearby. The dimensionality of the data has suggested a 1D structure <10 s. The 1D forward modeling has also been conducted to verify the results. The obtained model has also been compared with the drilled borehole in the area and they are in good agreement with it.