Gravity Modeling 2

1. Ali Oncel [email_address] Department of Earth Sciences KFUPM Gravity Modeling 2 Introduction to Geophysics Introduction to Geophysics-KFUPM Highest peaks on the planet

4. Introduction to Geophysics-KFUPM

5. Red Sea Arabian Gulf DSF Arabian Shield Gulf of Aden Zagros Suture GO AS MS OM Introduction to Geophysics-KFUPM

7. 2D Gravity Modeling  1 >  2  1  2  1 <  2  1  2 Introduction to Geophysics-KFUPM

8. Analogy between the gravitational attraction of the Earth from space and a sphere of anomalous mass buried beneath Earth’s surface. Earth’s gravitational acceleration ( g ) at a distant observation point depends on the mass of earth ( M ) and the distance R (from the center of mass to the observation point. Analogy between masses Introduction to Geophysics-KFUPM

9. The change in gravity ( Δ g ) due to a buried sphere depends on the difference in mass ( Δ m , relative to the surrounding material), and the distance ( R ) from the sphere to an observation point on Earth’s surface. Analogy between masses Introduction to Geophysics-KFUPM

10. Introduction to Geophysics-KFUPM

12. The magnitude of the gravitational attraction vector can be broken into horizontal and vertical components. Introduction to Geophysics-KFUPM

13. Introduction to Geophysics-KFUPM See pages 245-246 to see how that equation is derived since final equation is given here as: Horizontal component Vertical component

14. Following the substitutions in page 246 , the vertical component of the gravitational attraction, in which the gravimeter only can measure, is given as: Vertical component of gravitational attraction (mGal) Difference in density (g/cm 3 ) Radius of the sphere (m) Horizontal distance from the observation point Vertical distance from the distance (m) Introduction to Geophysics-KFUPM

15. Gravity anomaly profile ( Δ g z ): Buried Sphere Model Mass excess (+ Δ m, implying + Δ ρ ): causes an increase in gravity + Δ g z ), Mass deficit (- Δ m, implying - Δ ρ ): results in a gravity decrease ( - Δ g z ) Introduction to Geophysics-KFUPM

16. The more massive the sphere (larger Δ ρ /or larger R), the greater the amplitude ( l - Δ g z l ) of the gravity anomaly Gravity anomaly profile ( Δ g z ): Buried Sphere Model Introduction to Geophysics-KFUPM

17. The anomaly is attenuated ( smaller l Δ g z l ) as the sphere is buried more deeply within the Earth The width of gravity anomaly increases as the sphere is buried more deeply. Gravity anomaly profile ( Δ g z ): Buried Sphere Model Introduction to Geophysics-KFUPM (see more page 248 of Lillie’s book).

18. Introduction to Geophysics-KFUPM