Why do some earthquakes trigger tsunamis while others do not?
Quick Answer
Tsunamis form when an earthquake suddenly moves the seafloor up or down, displacing a large volume of water. Quakes that happen deep underground or that mainly slide sideways usually do not move enough water to create major tsunamis.
The Full Story
The biggest tsunami-generating earthquakes are usually shallow megathrust quakes at subduction zones, where one tectonic plate is forced beneath another. If the fault slip lifts or drops the seafloor over a broad area, the ocean surface is displaced and long waves radiate outward. The 2004 Sumatra-Andaman earthquake and the 2011 Tōhoku earthquake both produced devastating tsunamis because they involved large vertical seafloor movement. In contrast, many inland quakes, or those with mostly horizontal motion, do not significantly disturb the ocean floor.
Key Facts
YouTube Angle
Suggested video title for this topic:
"Not every big quake makes a tsunami — the secret is what the seafloor does."
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