Normal settlement and shifting debris, vibrations, and aftershocks can cause which type of collapse?

• A. Secondary
• B. Primary
• C. Tertiary
• D. Catastrophic

Answer: (A)

Secondary collapse happens after the initial failure, driven by the destabilization of damaged debris and loads already placed on the structure. Once the first collapse occurs, loose rubble, shifting masses, and weakened connections can settle, shift, or be jolted by vibrations or aftershocks. Those movements can trigger further failures in the damaged building, causing more of the structure to fall even though the main event has passed. Normal settlement and aftershocks are classic triggers for this ongoing, progressive collapse, which is why it’s the correct choice.