An unreinforced masonry (URM) building is a building made of brick, hollow concrete blocks, stone, or other masonry with no steel reinforcing bars embedded in it, making it susceptible to severe damage and collapse during an earthquake.

Non-ductile concrete buildings are structures that contain brittle concrete elements (columns, beams, walls, and connections) that tend to perform poorly during earthquakes due to the limited amount of provided reinforcing steel.

A soft or weak story wood-framed building is a multi-story wood structure where the first story is substantially weaker and more flexible than the stories above due to lack of walls or frames at the first floor.