Seismic design is a specific area of architecture dedicated to the structural analysis of buildings, bridges, and roads, with the aim of making them resistant to earthquakes and other seismic activity. Its ethical goal is the protection of the occupants and users of these structures. In an earthquake, unsound structures are more likely to collapse and cause damage. Heavily urbanized areas become more lethal because of the high density of structures and the threat of structural collapse. In this sense, structures can be viewed as heightening the danger created by any seismic activity and increasing the risk to life.
Seismic design must take into account the various effects produced by the ground motion that is caused by the earthquake. Duration, magnitude, and velocity are factors of seismic analysis that should be measured by architects, and each earthquake possesses its own unique danger. Nevertheless, the common element in the displacement of structures by the motion of earthquakes is the carrying over of the seismic force into the structures themselves, which is the reason structures are destroyed. The movement of the ground produces what is referred to as an inertial force within structures; the greater the mass of the structure, the greater is this inertial force, and hence the likelihood of destruction. The key becomes how the structures can absorb these forces in order to minimize damage, as opposed to being destroyed by them.
One of the approaches of seismic design is to produce more lightweight structures, due to the correlation between structural mass and inertial force. Selection of materials is critical to the process in order to minimize mass; yet the seismic designer must also be aware of local building codes and requirements when choosing material. These materials must also have good absorption ratings. Such materials are ductile and are able to move with the force of the earthquake and dissipate its impact. Materials with good absorption ratings are wood; steel frames; and reinforced walls, such as concrete or masonry, while pre-cast concrete frames are considered poor absorbers.
The type of structure being produced will also determine the requirements for successful seismic design. Buildings are more susceptible to damage than roads because of the concentration of seismic force in a more dense form. When designing buildings, the architect must calculate an equal distribution of mass in order to ensure that there is a center to the structure. This center affirms that the structure is grounded. Uneven distribution of mass will mean a destabilization of the building in the event of an earthquake.