Spatial Variation of Magnetotelluric Field Components in simple 2D and 3D Environments

Aa Onwuegbuchie

doi:10.4314/gjpas.v18i3-4.10

Abstract

The spatial variation of magnetotelluric field components over a buried three-dimensional conductive inhomogeneity is investigated numerically. The E-polarization mode electromagnetic field components were computed for different aspect ratios of the inhomogeneity and for different frequencies of the incident waves. The results show that as aspect ratio of the inhomogeneity is reduced the spatial variation of the electric field component Ex is reduced and that of the magnetic field component Hy is increased. Furthermore, the variation of Hy is strongly influenced by frequency as aspect ratio is reduced. Familiarity with these variations is important in understanding the behaviour of theoretically computed apparent resistivities which are useful in the interpretation of magnetotelluric field measurements for investigating geologic structures.KEYSWORDS: Spatial variation, E- polarization mode, Magnetotelluric field components, Electromagnetic field components, Three – dimensional, Two – dimensional, Aspect ratio.

Highlights

The electromagnetic (EM) field components measured at the Earth’s surface during a magnetotelluric (MT) survey are normally considered as raw data and are usually manipulated to yield such quantities as impedance, apparent resistivity, phase and other quantities which allow for meaningful physical interpretation (Linde and Pederson, 2004)
Horizontal transverse electric field components were computed for three aspect ratios of the inhomogeneity, namely 1⁄2, 1⁄4 and 0 (= 2D) and for three frequencies 0.556, 1.000 and 1.500 Hz using 2D and 3D computer programs of Daniyan (1983)
The normalized amplitudes of the horizontal electric and magnetic fields calculated along the profile in the symmetry plane through the centre and perpendicular to the long axis of the bodies are presented in Figures 3, 4 and 5

Summary

Introduction

The electromagnetic (EM) field components measured at the Earth’s surface during a magnetotelluric (MT) survey are normally considered as raw data and are usually manipulated to yield such quantities as impedance, apparent resistivity, phase and other quantities which allow for meaningful physical interpretation (Linde and Pederson, 2004). Stodt et al (1981) obtained horizontal MT field components over a buried conductive prismatic 3D body (aspect ratio = 1⁄2) and over the corresponding 2D body at three frequencies.

Results

Conclusion