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Chapter 2 The Earth s Gravitational field Global Gravity, Potentials, Figure of the Earth, Geoid Introduction Historically, gravity has played a central role in studies of dynamic processes in the Earth s interior and is also important in exploration geophysics. The concept of gravity is relatively simple, high-precision measurements of the gravity field are inexpensive and quick, and spatial variations in the gravitational acceleration give important information about the dynamical state of Earth. However, the study of the gravity of Earth is not easy since many corrections have to be made to isolate the small signal due to dynamic processes, and the underlying theory although perhaps more elegant than, for instance, in seismology is complex. With respect to determining the three-dimensional structure of the Earth s interior, an additional disadvantage of gravity, indeed, of any potential field, over seismic imaging is that there is larger ambiguity in locating the source of gravitational anomalies, in particular in the radial direction.

that levels the sea surface along an equipotential sur-face. g would point towards the center of the sphere. (Even in the presence of aspherical structure and rotation this is a very good approximation of g. However, if the equipotential is an ellipsoid, g = −∇U does not point to

  Equipotential