What is Geophysics?


What is Geophysics?

Definition: Geophysics is the study of the earth by quantitative physical methods.

Variations in rock physical properties allow us to investigate and (sometimes) image the structure of the earth. All such images can only show the effects of their own particular physical property contrasts and therefore all geophysical images are partial views of the earth. Some physical properties and the methods that exploit them are:

  • Density – Gravity, seismic
  • Magnetic susceptibility & remanence (ie magnetization) – Magnetic
  • Electrical conductivity/resistivity, magnetic susceptibility – Electromagnetic
  • Radioactivity – Gamma ray
  • Electrochemical polarizability, resistivity – Induced Polarization, Resistivity
  • Electrochemistry – Self Potential
  • Sound velocity – Seismic

These properties change at the earth’s surface, at boundaries between rock masses, at the water table, at gas/oil and oil/water interfaces, across zones of mineralisation, and within rock units (eg vertical and lateral density changes in sediments).

Low latitude magnetic anomaly
Low latitude magnetic anomaly

Gamma radiation, ternary diagram
Gamma radiation, ternary diagram