Solution:

Characteristics:

• The velocity of the wave depends on the depth of water where the seismic disturbance occurs. Initial wave velocity may be as high as 900 kilometers per hour (kph) (560 miles per hour [mph]), slowing to approximately 50 kph (31 mph) as the wave strikes land.

• Warning time depends on the distance from the point of wave origin.

• Speed of onset varies (see above).

• Impact on a shoreline can be preceded by a marked recession of normal water level prior to the arrival of a wave. This can result in a massive outgoing tide, followed by an incoming tsunami wave. People may be trapped when they investigate the phenomenon of the outgoing tide and then be struck by the incoming wave.

• The tsunami wave can be very destructive; wave heights of 30 meters have been known.

• The impact can cause flooding; saltwater contamination of crops, soil, and water supplies; and destruction of or damage to buildings, structures, and shoreline vegetation.

General countermeasures:

• Optimum arrangements for receipt and dissemination of warning;

• Evacuating threatened communities from sea-level/low-level areas to high ground, if a sufficient warning is available;

• Land-use regulations (but these are likely to be difficult to implement if the tsunami risk is perceived as rare); and

• Public awareness and education programs.

Special problem areas for disaster management:

• Timely dissemination of warning because of the possible short period between receipt of the warning and the arrival of the tsunami wave;

• Effective evacuation time scale;

• Search and rescue; and

• Recovery problems may be extensive and costly because of severe destruction and damage.