An earthquake causes a sudden transformation of energy, which converts the energy of deformation accumulated in the upper layers of the Earth’s crust into kinetic energy. The earthquake releases that energy through wave movements that are transmitted on the inside and on the surface of the Earth. This energy, attenuated by distance, must be absorbed by the structures of buildings and, in the case of severe earthquakes, dissipated. The State of current knowledge has allowed to develop regulations with bases for seismic design of structures with reasonable security for life, and even the application of economic criteria in the earthquake resistant design, opting for less strong than necessary structures. A structure subjected to a severe seismic movement can damage controlled, without going to collapse, and thus dissipate an important part of the absorbed energy, which means that by allowing degrade the structure you can save from collapse and protect the lives that are inside. Therefore, the seismic behaviour appropriate structure depends, in addition to its strength, its ability to dissipate energy from the moment in which their deformations exceed the elastic limit, i.e. of its ductility. Vulnerability to an earthquake is the poor behavior of a structure against an even moderate earthquake, due to a deficit of resistance and/or a low ductility.
The normative seismic, in general, support buildings are designed to resist strong earthquakes without collapse, even admitting severe structural damage. In the case of moderate earthquakes do not allow damage to structural elements, but damage in not structural elements such as walls, partitions, etc., and, in general, are easily repairable. In the case of slight earthquakes, the structure must not suffer any damage.