Key Concepts of Gravity Anomalies to Know for Intro to Geophysics

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.