• Seismic waves in the ocean and seawater cause high sea waves known as tsunami
• “Tsunami” is a Japanese term for “harbor wave”
• Tsunamis are generated by impulsive disturbances in a body of water
• They have extremely long wavelengths and long periods
• Tsunamis can cause considerable destruction in coastal areas affected by submarine earthquakes.
• For a Tsunami to occur, two conditions are required:
  • There should be an earthquake from which energy can be transferred.
  • There should be a vertical displacement of the water. i.e. during an earthquake, the crust should move vertically. That’s why Tsunamis are originated near oceanic trenches where plates are being subducted. In the Atlantic Ocean, a number of earthquakes occur on the Mid–Oceanic ridge but since there is no sudden vertical movement, Tsunamis are not formed. Tsunamis can also be triggered if the seamounts break. This can cause a vertical displacement of water.

Process of Generation of Tsunami

• Tsunamis have a low height to length ratio when first generated
• This allows them to go unnoticed beneath ships in the open sea
• As a tsunami approaches shore, its height rapidly increases due to rebound from the shallow surface
• Tsunamis can reach heights of over 30m in confined coastal waters close to their origin
• Tsunamis travel at speeds of 100-150 km/h in deep water, but can pick up to 650-900 km/h as they enter shallower water
• The speed of a tsunami is related to the depth of the water it is traveling through
• As a tsunami enters shallower water, its speed decreases and its height increases due to the shoaling effect
• The frequency of tsunamis is highest in the Pacific Ocean
• An International Tsunami Warning Network has been in operation around the Pacific Ocean since 1948 to alert coastal residents to possible danger.

Causes of Tsunami

• Earthquake
• Landslides
• Undersea Volcanoes
• Meteors, Asteroids
• Anthropogenic Factors Like Nuclear Explosions

Tsunami Early Warning System

• Science cannot predict when earthquakes will occur or when a tsunami will be generated
• Historical records and numerical models can help identify areas most likely to be affected by a tsunami
• The only effective way to mitigate the impact of a tsunami is through an early warning system
• A tsunami warning system (TWS) consists of a network of sensors to detect tsunamis and a communications infrastructure to issue timely alarms
• Early warning systems are installed globally, and governments use various means to warn citizens, including SMS messages, radio and television broadcasts, and sirens
• India’s Tsunami Early Warning Centre (ITEWC) was established in 2007 and is recognized as one of the best systems in the world
• ITEWC includes a real-time seismic monitoring network and receives earthquake data from all global networks to detect earthquakes (of M6.5)
• Since its inception in October 2007, ITEWC has monitored 339 earthquakes of M 6.5 and acts as one of the Regional Tsunami Advisory Service Provider (RTSP) along with Australia & Indonesia for the Indian Ocean region.