What is a tsunami?

A tsunami is a massive wave triggered by an earthquake or an underwater volcanic eruption as an earthquake or undersea volcanic eruption can cause a tsunami.

Tsunami waves do not dramatically increase in height or depth in the ocean. However, as the waves travel inland, they build up to ever-higher heights as the ocean’s depth decreases.

Tsunami waves’ speed depends on ocean depth rather than the distance from the source of the wave, according to the National Ocean Service.

When reaching shallow waters, Waves of Tsunami may travel like jet planes over deep waters, only slowing down.

What do we know about Japan’s earthquake and Tsunami?

A strong earthquake measuring 6.9 Richter scale struck the coast of Japan’s Miyazaki Prefecture on Monday. The quake was recorded at sea about seven miles southeast of the city of Miyazaki and prompted a tsunami advisory.

The US Geological Survey considered the quake’s preliminary magnitude at 6.8 while the Japan Meteorological Agency a Japanese scale of 0 to 7.

Japanese and American officials said the quake began at around 9:19pm (local time), with its epicentre a few miles offshore.

The Japanese weather agency issued a tsunami advisory for Miyazaki and Kochi prefectures. However, the authorities later withdrew the Tsunami advisory.

At least 20,000 were killed after the deadliest quake and later tsunami in  Japanese history struck northwest of the capital Tokyo in 2011.