Geological Geophysics - The Bedrock Conductivity Structure of the UK from AEM Data

Geological geophysics essentially refers to any geophysical map that is based on, or classified according to, existing geological knowledge. Here the geological classification of UK bedrock conductivity, derived from 5 airborne EM surveys conducted over 10 years is assessed. At a scale of 1:625k the UK digital bedrock geological lexicon comprises just 86 lithological classifications. The lowest common AEM frequency of 3 kHz is found to provide an 87% coverage (by area) of the UK lithologies. The geological classification is then extended to provide a new and complete 1:625k UK map of the near-surface bedrock conductivitity. Geological classifications inherently address grain size and clay/silt content of rock and these parameters also underpin theoretical descriptions of the materials electrical properties. When AEM conductivity data are examined on the basis of geological classification, they are found to be information rich. The challenge remains to successfully relate the bulk geophysical property variations to potentially more revealing lithological and physical characteristics.