By measuring Earth’s gravity field, we are able to map variations in the mass distribution of Earth’s crust. These variations are due to differences in the composition of the bedrock.
SGU uses gravity information primarily in bedrock mapping to delineate the distribution of different rock types. Gravity measurements have been acquired by SGU since the late 1950s.
The measurements are carried out at the ground surface and mainly along roads since cars are primarily used for transportation. Snowmobiles or helicopters are used in areas with sparse road coverage. Measurements can also be carried out on the ice of frozen lakes or sea during the winter. The aim is to acquire one measurement every 1 – 1.5 km when conducting regional gravity surveys. This is increased to about one measurement every 100 m in more targeted surveys.
The magnitude of the gravity value depends on the latitude, elevation above sea level (the geoid), geology, isostasy, the earth tide caused by the moon and sun’s gravitation, as well as the topography. Geophysicists and geologists are interested in the part of the gravity value that is affected by the mass distribution of Earth's crust, i.e. the geology. The gravity value is therefore reduced by these other factors in order to obtain only those gravity deviations which are related to the geology. These deviations are called terrain corrected Bouguer anomalies, which illustrate the mass distribution (density variation) of the subsurface down to great depths in Earth’s crust.