What phenomenon occurs when a building period coincides with the earthquake period?

The phenomenon where a building's natural frequency matches the frequency of ground motion during an earthquake is known as resonance. When resonance occurs, even relatively small vibrations from an earthquake can lead to significant oscillations in the structure, potentially resulting in extensive damage or failure. This is because the energy of the earthquake can constructively interfere with the energy in the structure, causing oscillations to increase in amplitude.

Understanding resonance is crucial in engineering and architecture as it emphasizes the importance of designing buildings to avoid frequencies that align with common seismic events. Structures that are designed with resonance in mind are more likely to withstand the forces exerted during an earthquake, thereby enhancing safety and structural integrity.