In flat-ground areas, earthquakes are commonly associated with which type of ground movement?

• A. Landslides
• B. Tectonic uplift
• C. Lateral spreads caused by liquefaction
• D. Subsurface cracking

Answer: (C)

In flat, water-saturated ground, earthquakes often trigger liquefaction, where the shaking raises pore-water pressure and drastically reduces the soil’s strength. When this happens in loose, granular sediments, the soil behaves more like a liquid than a solid. In such conditions, portions of the ground can move horizontally, producing lateral spreads across level terrain. This lateral displacement is a hallmark of liquefaction in flat areas, especially in river valleys, coastal plains, or fill zones where sands and silts are saturated.

Landslides need a slope to fail and slide material downslope, which isn’t typical in flat terrain. Tectonic uplift is a longer-term vertical movement associated with faulting, not the immediate surface response to shaking in flat ground. Subsurface cracking can occur, but the distinctive, widespread horizontal movement across level ground due to liquefaction best explains the observed ground movement in flat areas during earthquakes.