The seismic vulnerability is the tendency of a structure to encounter damage and failure due to a seismic action. The more a building is vulnerable (due to construction methods, design, quality of the materials and maintenance), the more severe will be the consequences on the structure itself in case an earthquake occurs. The legislation in force imposes the respect of earthquake resistant criteria requiring a ductile behavior of the structures in response to the solicitation, so that the buildings have a low seismic vulnerability.

This property of the construction is represented by the definition of the parameter ζE, that is the ratio between the maximum seismic action that the structure can sustain and the one that would be used for the design of a new construction.