The cause of tsunami appeared after the earthquake

Seismic ocean floor can only create tsunamis under certain conditions .

Tsunami-turned ships at a port in Hachinohe City, Aomori Prefecture on March 11.
Photo: AFP.

Tsunami struck Japan after the strongest earthquake in 140 years occurred in the island nation. Immediately after the earthquake occurred, Japanese officials issued a tsunami warning.

Livescience said the tsunami could be formed when seabed strata collided with each other to cause an earthquake.

If a strong shock occurs on the ocean floor, one or more strata can be lifted or slumped, causing the water above to rise or fall. Large waves formed soon after in both cases. Thus, when one or more areas of the ocean floor rise or fall sharply, tsunamis can form.

For many reasons, it is impossible to predict the appearance of tsunamis after earthquakes outside the ocean. Normally, if an earthquake occurs, scientists cannot immediately know its impact on the ocean floor, but wait a few hours later. In addition, humans cannot detect tsunamis if we are in the ocean, because they only show strength when approaching the shore.

Not every earthquake in the sea floor causes tsunamis. Experts say, tsunamis only occur after earthquakes thanks to a combination of the following three factors: seismic intensity, displacement direction of the stratigraphic plate and seabed terrain. The possibility of formation of tsunamis will be very low if the collision between the stratigraphic plates is very deep compared to the ocean floor, the stratigraphic array only moves slightly vertically, the stratigraphic array travels horizontally.

The stronger the sea floor moves vertically, the higher the height of the tsunami. The strength of the tsunami will increase to a terrible level if the epicenter of the earthquake lies at the bottom of the ocean and the stratigraphic array moves strongly vertically. The 2004 tsunami in the Indian Ocean and in 1964 on the Atlantic Ocean were waves capable of crossing the ocean. When spreading on the ocean surface, tsunamis often reach close speeds by jet, meaning from 800 to 1,000 km / h. But when approaching the mainland the tsunami speed decreases.

The US Geological Survey confirmed that, except for the biggest tsunamis, such as the tsunami in the Indian Ocean in 2004, most tsunamis did not bring huge waves. Instead they hit the land in the form of very strong and fast tides. When spreading on the surface of the ocean, their altitudes are only a few centimeters. But when approaching the shore, the force at the bottom of the sea can turn them into waves of height into meters.