This is a good example of why earthquake action should not be understood as a simple imposed lateral load.

This is a good example of why earthquake action should not be understood as a simple imposed lateral load.

During an earthquake, ground motion excites the entire structural system. The mass of each floor generates inertia forces, and those forces are resisted by the lateral-force-resisting system. As the effects accumulate down the height of the building, the lower storeys and the base region often experience the highest shear demand, overturning effects, axial load interaction, inter-storey drift concentration and P-Delta effects.

This may explain why the lower levels in the video appear to have sustained much more significant damage than the upper levels.

However, the actual mechanism still requires proper structural assessment. Possible contributing factors may include a weak or soft storey, inadequate confinement, discontinuous walls, poor column or joint detailing, short-column effects, construction defects, prior damage from the first earthquake, or cumulative damage caused by the doublet sequence.