How are tsunamis generated and what mechanisms are associated with subduction zones?

• A. Tsunamis form from meteor impacts
• B. Tsunamis form from sudden vertical displacement of the sea floor, often during megathrust earthquakes
• C. Tsunamis are generated by deep-focus earthquakes only
• D. Tsunamis occur only near coasts

Answer: (B)

Tsunamis are caused when a large amount of seawater is displaced rapidly, which happens when the seafloor moves abruptly during an earthquake at a subduction zone. The locked megathrust fault between the converging plates ruptures, often uplifting or subsiding the ocean floor, and this vertical seabed movement quickly pushes the overlying water column. The displaced water forms waves that travel across the ocean and grow taller as they reach shallower coastal waters. This mechanism is the hallmark of subduction zone activity, especially during megathrust earthquakes. Other ideas—like meteor impacts or deep-focus earthquakes—don’t fit because they either don’t cause the dramatic vertical seabed displacement needed to move the entire water column in the open ocean, or they occur too deep to significantly affect the seafloor. Tsunamis are not restricted to near-coast generation; they can traverse oceans and impact distant shores.