g is the acceleration of gravity 9.8 (m/s²) or the strength of the gravitational field (N/kg) (which it turns out is equivalent). G is the proportionality constant 6.67x10^-11 (N-m²/kg²) in Newton's law of gravity. On the other hand, the force of gravity, or F = mg, at the surface of the earth, or F = GMm/r^2 at a distance r from the center of the earth (where r is greater than the radius of the earth). When there is an earthquake, the forces caused by the shaking can be measured as a percentage of gravity, or percent g.

Gravity
The attraction between two masses, such as the earth and an object on its surface. Commonly referred to as the acceleration of gravity. Changes in the gravity field can be used to infer information about the structure of the earth's lithosphere and upper mantle.

Geodesy is the science of determining the size and shape of the earth and the precise location of points on its surface.

Geodetic
Geodetic refers to the use of geodesy for measurements.

Geology is the study of the planet earth -- the materials it is made of, the processes that act on those materials, the products formed, and the history of the planet and its life forms since its origin.

Geomorphology is the study of the character and origin of landforms, such as mountains, valleys, etc.

Geophysics is the branch of earth science which employs physical measurements and mathematical models to explore and analyze the structure and dynamics of the solid Earth and similar bodies and their fluid envelopes.
 

Geotechnical means referring to the use of scientific methods and engineering principles to acquire, interpret, and apply knowledge of earth materials for solving engineering problems.

A graben is a down-dropped block of the earth's crust resulting from extension, or pulling, of the crust.

The term ground failure is a general reference to landslides, liquefaction, lateral spreads, and any other consequence of shaking that affects the stability of the ground.

Ground motion is the movement of the earth's surface from earthquakes or explosions. Ground motion is produced by waves that are generated by sudden slip on a fault or sudden pressure at the explosive source and travel through the earth and along its surface.