Japan earthquake: What is a tsunami? How does it differ from ocean waves and what does ‘tsunami’ mean in Japanese?

The Japan Meteorological Agency has issued a tsunami warning for Fukushima following a powerful earthquake.

The earthquake has a Richter scale of 7.3, which is on the major end of the scale and has struck more than 35 miles below the sea off the coast of Fukushima.

The magnitude of the earthquake has alerted a tsunami warning and it is the same area which fell victim to a 9.0 earthquake in March 2011, leading to a tsunami that resulted in a nuclear plant accident.

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Here is everything you need to know about tsunamis.

A tsunami hazard zone sign is displayed near a beach. (Pic credit: Patrick T Fallon / AFP via Getty Images)

What is a tsunami?

A tsunami, which is the Japanese word for ‘harbour wave’, is a series of waves in a body of water which are triggered by a displacement of a large volume of water, usually in an ocean or a large lake.

These natural disasters that cause tsunamis are earthquakes, volcanic eruptions, landslides, glacier calvings, meteorite impacts and many other underwater explosions above or below water level.

Tsunamis differ from ocean waves as normal waves are caused by wind or tides, which are generated by the gravitational pull of the moon and the sun, whereas a tsunami is triggered by the displacement of water by a large event.

A tsunami is often described as a tidal wave due to its resemblance to a rapidly rising tide, however, this term is discouraged by scientists as it may give the wrong impression of a casual relationship between tides and tsunamis.

Geologists, oceanographers and seismologists investigate each earthquake based on multiple factors, however, there are some warning signs of a future tsunami, as well as automated systems that can provide warnings immediately following an earthquake in time to save lives.