Terms You Should Know About Tsunamis



A series of very large sea waves caused by a natural disaster such as an earthquake or an undersea volcanic eruption or an explosion.


Any tsunami that travels over 1,000 kilometers from its point of origin before reaching land.


The point on Earth's surface directly above the point where an earthquake or underground explosion occurs.

Tsunami Warning System

Systems designed to detect forming tsunamis and issue advance warnings in time for preventative measures to be taken.

Seismic Waves

Shockwaves sent through the Earth, created by an earthquake or explosion.


Relatively small, very fast moving seismic waves that appear first on a seismogram.


Larger, slower moving waves that travel in the shape of a shifting "S". These seismic waves appear second on a seismogram.


A graph produced by a seismograph machine, a tool that records ground motion and shifting during an explosion or earthquake.

Sumatra, Indonesia

The region most directly affected by the tsunami on December 26, 2004. 168,000 people died in Indonesia alone.

Simeulue Regency

The island off the western coast of Sumatra, Indonesia where the 2004 Indian Ocean Tsunami began.


The periodic variation in the surface level of the oceans and of bays, gulfs, inlets, and estuaries, caused by gravitational attraction of the moon and sun.


The scientific study of oceans, the life that inhabits them, and their physical characteristics, including the depth and extent of ocean waters, their movement and chemical makeup, and the topography and composition of the ocean floors. Oceanography also includes ocean exploration. Also called oceanology.

Tsunami Advisory

Issued when an earthquake has just taken place in the Pacific basin, which could generate a tsunami.

Tsunami Warning

Issued when an earthquake generated a tsunami and the residents in the area where the tsunami hit are strongly advised to evacuate.

Tsunami Watch

Issued when a tsunami may have been generated by a tsunami, but it is at least two hours away from the area.


The National Tsunami Hazard Mitigation Program