A tsunami that originates close to the coast and arrives quickly is called a local tsunami. Because its source is nearby, the first waves may reach shore within minutes, leaving little time for official warnings.
Local tsunamis are commonly caused by large earthquakes beneath or near the seafloor, especially where tectonic plates meet. The earthquake suddenly lifts or drops the seabed, displacing the water above it and sending waves toward nearby coastlines.
The term is about travel distance and warning time, not necessarily the tsunami's total size. A local tsunami can be extremely destructive even if it affects only one stretch of coastline. People near the source should rely on natural warnings—strong or prolonged shaking, a sudden sea-level change, or an unusual ocean sound—and move to higher ground immediately.
A common mix-up is “tidal wave.” Tsunamis are not caused by tides; they are waves produced by sudden water displacement. A tsunami from a distant source is classified as a distant tsunami or teletsunami.