Prediction and Early Warning
For areas located at great distances from earthquakes that could potentially generate a tsunami there is usually plenty of time for warnings to be sent and coastal areas evacuated, even though tsunami travel at high velocities across the oceans. Hawaii is good example of an area located far from most of the sources of tsunami, where early warning is possible and has saved lives. For earthquakes occurring anywhere on the subduction margins of the Pacific Ocean there is a minimum of 4 hours of warning before a tsunami would strike any of the Hawaiian Islands.
The National Oceanic and Atmospheric Administration (NOAA) has set up a Pacific warning system for areas in the Pacific Ocean, called the Pacific Tsunami Warning Center. It consists of an international network of seismographic stations, and tidal stations around the Pacific basin that can all send information via satellite to the Center located in Hawaii. When an earthquake occurs somewhere in the region, the Center immediately begins to analyze the data looking for signs that the earthquake could have generated a tsunami. The tidal stations are also monitored, and if a tsunami is detected, a warning is sent out to all areas on the Pacific coast. It takes at least 1 hour to assimilate all of the information and issue a warning. Thus for an average velocity of a tsunami of 750 km/hr, the regional system can provide a warning sufficient for adequate evacuation of coastal areas within 750 km of the earthquake.
In order to be able to issue warnings about tsunami generated within 100 to 750 km of an earthquake, several regional warning centers have been set up in areas prone to tsunami generating earthquakes. These include centers in Japan, Kamchatka, Alaska, Hawaii, French Polynesia, and Chile.
These systems have been very successful at saving lives. For example, before the Japanese warning system was established, 14 tsunami killed over 6000 people in Japan. Since the establishment of the warning system 20 tsunami have only killed 215 people in Japan.
Like all warning systems, the effectiveness of tsunami early warning depends strongly on local authority’s ability to determine that there is a danger, their ability to disseminate the information to those potentially affected, and on the education of the public to heed the warnings and remove themselves from the area.
The Biggest Tsunamis in The Last Century
The biggest Tsunami Magnitude in the last century was probably the 1960 Chile tsunami. The tsunami magnitude refers to the amount of energy released during generation and corresponds roughly to the largest amount of water moved.
The tsunami wave with the highest runup (biggest splash) in the last century was probably at 1958 Lituya Bay, Alaska.
The tsunami that caused the most damage and human casualties in the last century is the recent 2004 Aceh Sumatra tsunami.
These are only the tsunamis for which there are historical facts and measurements. Other tsunamis have occured throughout history and pre-history that were most likely bigger than the ones listed above.