Geological Geophysics - An Example Using AEM Data

Geophysical information, when spatially extensive, can be used to examine the relationships that may exist between geological classification schemes and their geophysical responses and/or properties. Geological geophysics essentially refers to any geophysical map that is based on, or classified according to, existing geological knowledge. Here the geological classification of subsurface values of conductivity, derived from airborne EM survey data, is assessed using survey data obtained across a small (36 x 22 km) area in the south of England. The characteristics of the highest frequency (closest to outcrop) conductivity distributions are examined in relation to two existing sedimentary bedrock classification schemes. Geological classifications of the data are found to explain over 75% of the variability in observed values. It is then demonstrated how the central moments and dispersion statistics of the distributions obtained can be used to predict the continuous near-surface conductivity distribution across a major area of southern England containing, as it does, a high population density and extensive infrastructure.