base shear
The shearing force developed at the base of a structure by the tendency of its upper mass to remain at rest while the base is translated by ground motions during an earthquake. Base shear is the minimum design value for the total lateral seismic force on a structure, and is assumed to act nonconcurrently in the direction of each of the main axes of the structure. It is computed by multiplying the total dead load of the structure by a number of coefficients to reflect the character and intensity of the ground motions, the mass and stiffness of the structure and the way these are distributed, the type of soil underlying the foundation, and the pressure of damping mechanisms in the structure. (Ching, 1995)