After a 7.6 magnitude earthquake hit north-central Japan Tsunami waves hit several parts of Japan’s coastal areas.

             The word tsunami (pronounced tsoo-nah’-mee) is composed of the Japanese words “tsu” (which means harbor) and “nami” (which means “wave”). Tsunami is a series of large waves of extremely long wavelength and period usually generated by a violent, impulsive undersea disturbance or activity near the coast or in the ocean ; caused by earthquakes or volcanic eruptions under the sea. When a sudden displacement of a large volume of water occurs, or if the sea floor is suddenly raised or dropped by an earthquake, big tsunami waves can be formed.  The waves travel out of the area of origin and can be extremely dangerous and damaging when they reach the shore. 

        Often the term, “seismic or tidal sea wave” is used to describe the same phenomenon, however the terms are misleading, because tsunami waves can be generated by other, non seismic disturbances such as volcanic eruptions or underwater landslides, and have physical characteristics different of tidal waves. The tsunami waves are completely unrelated to the astronomical tides – which are caused by the extraterrestrial, gravitational influences of the moon, sun, and the planets. Thus, the Japanese word “tsunami”, meaning “harbor wave” is the correct, official and all-inclusive term.

An earthquake is the result of a sudden release of energy, an intense shaking of Earth’s surface, in the Earth’s crust that creates seismic waves. The shaking is caused by movements in Earth’s outermost layer(Crust).

The location where an earthquake begins is called the epicenter. An earthquake’s most intense shaking is often felt near the epicenter.

The energy from an earthquake travels through Earth in vibrations called seismic waves. Scientists can measure these seismic waves on instruments called seismographs.

The magnitude of an earthquake, total amount of energy released by earthquake, is conventionally reported using the Richter scale or a related Moment scale (with magnitude 3 or lower earthquakes being hard to notice and magnitude 7 causing serious damage over large areas)

Another way to measure the strength of an earthquake is to use the Mercalli scale. Invented by Giuseppe Mercalli in 1902, this scale uses the observations of the people who experienced the earthquake to estimate its intensity based on amount of damage
to various types of structures.

Three main types of waves are produced during the earthquake: Primary waves or P, Secondary waves or S and Long waves or surface waves or L.

                L waves are responsible for most of the the destruction caused by an earthquake. P and S waves in the study of earth’s interior.

                 
   The  P waves travel fastest and first to reach seismic station, and after that the S waves which are the slowest arrive. P waves is a longitudinal wave: in which the particle
displacement is parallel to the direction of wave propagation. P wave is also called compression -dilation. Like the sound waves, the P waves pass through solids, liquids, and gases alike.

                 The S waves are Transverse waves: the particle displacement is perpendicular to the direction of wave propagation. The S waves pass through only  solids.