One‐Dimensionl Inversion of Magnetotelluric Field Data by SIS and Occam's Inversion Technique: A Case Study from the Indian Himalaya

Abstract

Electromagnetic method is one of the most effective geophysical methods in earth crust and mantle structure studies. Magnetotelluric (MT) data are used to obtain resistivity image of earth's surface on the depth scale of few hundred of meters to several tens of km. One-dimensional (1D) MT inversion is carried out to estimate electrical resistivity variation of earth's surface with depth. In the present research paper one-dimensional inversion of MT sounding curves is carried out on nine sites in foothill of Himalaya near Roorkee to Hardwar region. A non-iterative and minimum norm estimator based algorithm Straight forward Inversion Scheme (SIS) is used to obtain continuous smoothest resistivity depth model. Another iterative and minimum norm estimator based algorithm Occam's inversion scheme is also used to obtain smoothest one-dimensional inversion model. The data is inverted for both TE- and TM-mode of polarization. The inverted data shows one-dimensional behavior of subsurface resistivity up to depth about 0–15 km with resistivity variation ≈10–100 ohm-m in both modes of polarization and after that the subsurface structure is two-dimensional in both modes. 1D inversion of data provides a good starting model to reduce the computational cost of two-dimensional inversion.