The use of gravity measurements as a tool to aid geological understanding relies on the detection of the small variations in the Earth’s gravitational field that are due to lateral contrasts in density between rocks. Depending on the underlying geological causes, these contrasts arise at a range of depths from the near-surface to more than 100 km. Variations in gravity are measured using instrumentation and techniques that include land gravity surveys, ship and aircraft based platforms and satellite altimetry. Gravity data are presented as anomalies after removal of non-geological effects such as the rotation of the earth, earth tides and the relative elevation of measurements. Further processing may involve calculating and removing the gravitational attraction of topography and the gravity effects due to an isostatic model of topographic relief. Filtering and image processing techniques are commonly used to enhance portions of the gravity anomaly field.
Chapter 3 presents a regional overview of gravity anomalies over the North Atlantic, including free air, bouguer, and isostatic anomalies and a map of the tilt derivative of the isostatic anomaly that highlights major structures of the region.