Gravity

Springtime gravity survey in Labrador.

Gravity surveys map the variations in the gravitational field of the earth. All gravity variations come from horizontal variations in density.

Gravity can be used to put realistic bounds on the size, shape and depth of an anomalous body, determined from the irregularities in the gravitational field.

In honour of Galileo, the unit of acceleration of gravity was named the Galileo or Gal. We use the Lacoste and Romberg land gravity meter, which is capable of measuring 0.01 mGal - or 1 part in 100 million - of the earth's gravitational acceleration.

Magnetics

Winter magnetic survey.

Magnetic surveys map variations in magnetic fields below the surface. The magnetic anomalies due to basement topography have distinctive characteristics. Even though the amplitudes of these anomalies are small, they can be reliably detected in high quality magnetic data sets. The magnitude of the basement relief can only be estimated, because the effects of variations in rock magnetism and the magnitude of relief cannot be separated when the relief is very small compared to the depth of burial. However the horizontal dimensions and locations of basement relief can be determined with great precision.

The location of subtle basement relief is often of great exploration value in the search for hydrocarbon traps. Basement features, whether due to fault motion or paleoerosion, can often set up the conditions for hydrocarbon traps in the overlying sedimentary section.