Tsunami waves can travel large distances causing destruction thousands of miles away from their initiation point. They carry enormous energy as they involve movement of the entire water column from the ocean surface to the seafloor. Tsunami waves travel at speeds of 800-1000 km per hour in the deep ocean and have wavelengths of 100-500 km. The wave height in the deep ocean may be around only 10 cm but as it approaches the shore, it may grow to 10 metres or more.

The majority of deaths associated with tsunamis are related to drowning, but traumatic injuries are also a primary concern. Injuries such as broken limbs and head injuries are caused by the physical impact of people being washed into debris such as houses, trees, and other stationary items. As the water recedes, the strong suction of debris being pulled into large populated areas can further cause injuries and undermine buildings and services.

 

Early warning

There is still no reliable way to predict earthquakes accurately despite many years of research internationally, but statistics and geological knowledge can indicate where large earthquakes are likely and what their effects will be. In the past 20 years or so, with support from Government and industry scientists have developed systems to detect and locate earthquakes and transmit alerts. Near real-time, 24-hour, seismic monitoring and information services are in operation [2,3,4].

Once a potentially tsunamigenic earthquake has occurred, automated analysis can generally provide the location, magnitude, and faulting mechanism within minutes. This provides the source term for tsunami modelling which give estimates of the arrival time and wave height at locations in the tsunami's path. Tsunamigenic earthquakes often occur at subduction zones close to ocean-continental boundaries and the nearby coastline may be inundated within minutes giving little time to respond to earthquake alerts. However, the wave directed away from land may take many hours to arrive at distant targets across the oceanic basin giving local and national authorities the opportunity to mobilise and implement emergency plans.
 

1. Kanamori, H., Mechanism of tsunami earthquakes, Phys. Earth Planet Interiors 1972
   6, 346-359, quoted in Department for Environment, Food and Rural Affairs The threat posed by tsunami to the UK. Kerridge, D on behalf of British Geological Survey, HR Wallingford, Met Office and Proudman Oceanographic Laboratory consortium  Study commissioned by Defra Flood Management June 2005.
2. Walker A, UK-wide vibration monitoring by the British Geological Survey Chemical Hazards and Poisons Report January 2008:11;12-15.
3. Bossu R, Walker A. New tools for alerts and capturing immediate effects of rapid-onset events across Europe Chemical Hazards and Poisons Report April 2009: 14: 35-37.
4. The USGS National Earthquake Information Centre

• Summary of initial health effects from tsunamis
  In summary the health impacts arise from waters full of swirling debris with falling structures which will lead to crush injuries, fractures, and a variety of open and closed wounds.
  Added/updated: 11 March 2011
  
• Recent major tsunamis
  Summary of recent tsunamis, and HPA responses.
  Added/updated: 18 March 2011