Due to the transient nature of peak ground motion,
the soil structure may experience only a finite displacement
rather than a complete structural failure even when
the dynamic factor of safety momentarily drops below
one during a seismic event. The pseudo-static approach
is incapable of quantifying the extent to which the soil
structure has displaced. This inadequacy has long been
recognized and many displacement-based methods
(the second category) have been developed as alternative
approaches, or extensions, to the pseudo-static
approach. 2'9-21 Displacement-based methods require a