Destructive tsunamis are most commonly produced by earthquakes along which tectonic setting?

• A. Mid-ocean ridges
• B. Subduction zones
• C. Continental rifts
• D. Intraplate hotspots

Answer: (B)

Tsunamis from earthquakes mainly come from rapid vertical movement of the sea floor. The biggest and most destructive tsunamis occur when large portions of the ocean floor are abruptly uplifted or dropped along a long, shallow fault. This is typical of subduction zones, where one tectonic plate dives beneath another and rupture can occur along a wide megathrust fault. The sudden vertical displacement of vast amounts of seawater sends powerful waves traveling across oceans and driving enormous coastal flooding.

Mid-ocean ridges involve spreading and mostly horizontal motion, and while earthquakes can occur there, the vertical seafloor movement is generally smaller and less capable of displacing water on a scale that produces devastating tsunamis. Continental rifts involve tensional failure that also tends to produce less dramatic seafloor displacement offshore. Intraplate hotspots can generate earthquakes or landslides, but significant tsunami disasters are much less common unless a large submarine landslide or volcanic flank collapse accompanies the event.

Historical megathrust earthquakes in subduction zones—like those off Sumatra and Japan—illustrate how the combination of extensive rupture, shallow depth, and vertical seafloor motion yields the largest, most destructive tsunamis.