Which of the following earthquake hazards would be of immediate concern to communities built on compacted sediment?

Communities built on compacted sediment face significant risks during an earthquake, and liquefaction is a critical hazard in this context. Liquefaction occurs when saturated, unconsolidated sediments temporarily lose strength and behave like a liquid due to seismic shaking. This phenomenon is particularly concerning for areas with loose, water-saturated sediments, such as silts and sands, that are susceptible to this effect.

When an earthquake strikes, the energy released can cause the ground to shake violently, and in situations where the sediment is both compacted and saturated, the vibrations can lead to a loss of stability. Buildings and infrastructure that are constructed on such sediment may experience severe damage or even collapse as the ground beneath them effectively turns into a liquefied state, leading to significant ground displacement.

While other hazards like tsunamis, landslides, and ash clouds present risks in certain contexts, they are not as directly associated with compacted sediment as liquefaction is. Tsunamis typically affect coastal areas, landslides relate more to steep slopes, and ash clouds are a concern in volcanic regions. Therefore, liquefaction is the most immediate hazard for communities situated on compacted sediments during an earthquake.