NEAR-SURFACE RESISTIVITY AND RMT STUDIES AT SELECTED SITES IN UTTARAKHAND, INDIA

Abstract

Some Direct Current (DC) resistivity and Radiomagnetotelluric (RMT) studies were conducted at selected sites in Uttarakhand, India. These techniques are useful in delineating near-surface resistivity structure. In resistivity methods, a new quasi-field experiment was designed for a comparative study of non-traditional and traditional electrodes array. Field ERT data were also recorded and interpreted in the first resistivity structure and subsequently geological characterization of resistivity values. Some synthetic numerical studies were also added to determine the effects of nearby anomalous resistivity structure on ERT data. Finally, RMT studies were conducted in the Himalayan Frontal Thrust (HFT) zone in the Mohand area. The entire study comprises four different parts, (i) Comparative study of the imaging capacity of the four-electrode traditional and non-traditional (quasi-null) arrays using quasi-field analogue modelling experiments, (ii) ERT field studies in Piedmont Zone(PZ) and Himalayan Frontal Thrust (HFT) zone in and around Mohand, Dehradun region, (iii) Effects of nearby arbitrary resistivity inhomogeneity (2D/3D) on the ERT profile data using numerical modelling and inversion experiment, and (iv) RMT data studies in and around HFT zone in Mohand, Dehradun region. The first part is the quasi-field analogue modelling experiment designed and implemented a comparative study of the imaging capacity of quasi-null arrays and the traditional arrays. For this purpose, a free-air analogue modelling laboratory was designed. This enabled one to control the parameters of the body and carry out measurements in field conditions as a reliable method to verify the field applicability of a non-traditional array. The imaging capacity of the four-electrode traditional array, the Dipole-dipole (Dp-Dp), was compared to that of the special configurations, three members of the series of the 11n quasi-null arrays. The effects of a dipping and finite length of the 2D prismatic body were investigated in Electrical Resistivity Tomography (ERT) measurements. Since the available conventional processing and inversion codes were not able to handle quasi-null array, a different code Res2D-Hu was used.