Insitu Rock Conductivity Measurement - EM Approach

Insitu electrical conductivity measurements were made over Deccan Traps using EM38 ground conductivity meter The equipment is a light weight dipole - dipole system wIth a coil separation of 1 m utilizing a frequency of 146KHz The measurements were made over chosen lava flow Units viz, compact basalt, amygdaloidal basalt and redbole The statistical analysis shows that (1) the mean resistivity of amygdaloldal basalt is 38 Ωm (range 25-42 Ωm), (2) the mean resistivity of the compact basalt under whIch a thm redbole is present is 113 Ωm, (range 105 - 131 Ωm), (3) the mean resistivity of red bole which is present under the compact basalt is 11 Ωm (range 10-13 Ωm) and (4) all the lnsitu resistivities show lognormal dIstnbution.

The EM approach conductivity values (converted to resistivity values) compare well with the earher reported mwu resistivity values usmg DC resistivity measurements (Sathyamurthy, 1985) However, the values of the resistivity obtamed on bulk samples In the laboratory show markedly higher values Synthetic MT/CSAMT data generated using the insitu resistivity values obtamed via EM approach is utilized to estimate the errors In the Inverted geoelectnc parameters of resistivity and thickness.