Key Concepts of Gravity Anomalies

Gravity anomalies reveal variations in the Earth's gravitational field, helping us understand subsurface density and geological structures. Key concepts like Bouguer and free-air anomalies provide insights into tectonic processes, resource exploration, and the Earth's internal composition.

1. Bouguer anomaly

   • Represents the gravity anomaly corrected for the gravitational attraction of topography.
   • Accounts for the mass of material above sea level, providing a clearer picture of subsurface density variations.
   • Useful in identifying geological structures and mineral deposits.

2. Free-air anomaly

   • Measures the difference between observed gravity and the theoretical gravity at a given elevation.
   • Corrects for elevation but not for the mass of the terrain above the measurement point.
   • Helps in understanding large-scale geological features and tectonic processes.

3. Isostatic anomaly

   • Reflects the gravitational effects of the Earth's crust's buoyancy and compensation mechanisms.
   • Indicates areas where the crust is either thicker or thinner than expected, often related to tectonic activity.
   • Important for studying mountain ranges and oceanic basins.

4. Regional gravity anomaly

   • Represents the long-wavelength variations in gravity over large areas, typically reflecting geological features.
   • Helps in understanding the broader geological context and tectonic settings.
   • Useful for regional geological mapping and resource exploration.

5. Residual gravity anomaly

   • The difference between the observed gravity and the regional gravity anomaly.
   • Captures short-wavelength variations, often related to local geological structures.
   • Important for detailed exploration of mineral resources and subsurface features.

6. Terrain effect

   • Refers to the gravitational influence of topography on gravity measurements.
   • Can introduce significant errors if not properly accounted for in gravity surveys.
   • Essential for accurate interpretation of gravity data in mountainous or rugged areas.

7. Mass deficiency

   • Indicates a region where the gravitational attraction is lower than expected due to a lack of mass.
   • Often associated with features like sedimentary basins or areas of erosion.
   • Important for understanding subsurface geology and resource potential.

8. Mass excess

   • Represents areas where the gravitational attraction is higher than expected due to an excess of mass.
   • Commonly found in regions with dense geological formations or volcanic activity.
   • Useful for identifying potential mineral deposits and geological anomalies.

9. Gravity gradient

   • Measures the rate of change of gravity with respect to distance, providing insights into subsurface density variations.
   • Helps in identifying geological boundaries and structures.
   • Important for detailed geophysical surveys and resource exploration.

10. Geoid undulation

    • Describes the deviation of the Earth's geoid from a reference ellipsoid, reflecting variations in gravitational field.
    • Provides insights into the distribution of mass within the Earth, including oceanic and continental features.
    • Important for understanding sea level changes and Earth's internal structure.