Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters - by Dr. George Pararas Carayannis

Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters


Tsunami Forecasting, Preparedness and Warning

George Pararas-Carayannis

(Excerpts from a Paper Presented at the Fifteenth Conference on Broadcast Meteorology of the American Meteorological Society, April 9-12, 1985, Honolulu, Hawaii)

Copyright © 2005. All Rights Reserved


Tsunami hazard mitigation precludes accurate and expeditious forecasting, issuance of a prompt warning, and a program of preparedness that will assure the effectiveness of the warning.

Forecasting tsunamis requires adequate understanding of the phenomenon, good and expeditious collection of earthquake and sea level data, and accurate assessment and interpretation of this data.

In order for a tsunami warning to be of value, an expeditious and effective international communications system is necessary to insure proper dissemination throughout a large geographical area. Civil Defense Agencies collaborating into the International Tsunami Warning System, must have good emergency operations plans for their own countries or territories, efficient internal communications and a program of tsunami preparedness which includes organizational infrastructural coordination and comprehensive public education.

Historical Background

Tsunamis are among the most terrifying natural hazards known to man and have been responsible for tremendous loss of life and property throughout history. Because of their destructiveness, tsunami have important impact on the human, social and economic sectors of our societies. In the Pacific Ocean where the majority of these waves have been generated, the historical record shows tremendous destruction. In Japan, which has one of the most populated coastal regions in the world and a long history of earthquake activity, tsunami have destroyed entire coastal populations. There is also a history of tsunami destruction in Alaska, in the Hawaiian Islands in South America and elsewhere in the Pacific, although the historic records for these areas do not go back sufficiently in time.

Historical records also document considerable loss of life and destruction of property on the western shores of the North and South Atlantic, the coastal regions of north-western Europe, and in the seismically active regions around the eastern Caribbean. Fortunately tsunami in the Atlantic and the Caribbean do not occur as frequently as in the Pacific.

Destructive tsunami have occurred also in the Indian Ocean and in the Mediterranean Sea. The most notable tsunami in the region of the Indian Ocean was that associated with the violent explosion of the volcanic island of Krakatoa in August 1883. A 30 meter (100 feet) tsunami resulting from this explosion killed 36,500 people in Java and Sumatra. The violent eruption and explosion of the volcano of Santorin, in the fifteenth Century B.C. generated a tremendous tsunami which destroyed most of the coastal Minoan settlements on the Aegean sea islands acting as the catalyst for the decline of the advanced Minoan civilization.

Japan is very vulnerable to the tsunami hazard. All the major Japanese islands have been struck by devastating tsunamis. A total of 68 destructive tsunami have struck Japan between A.D. 684 and 1984 with thousands of lives lost and with the destruction of-hundreds of villages. In this century alone, at least 6 major destructive tsunamis have hit Japan. On 3 March 1933 a tsunami in the Sanriku area reached a height of about 30 meters and killed over 3,000 people, injured hundreds more and destroyed approximately 9,000 homes and 8,000 boats. Other similarly destructive tsunami occurred in 1944, 1946, 1960, and in 1983. The 1983 event, although not very destructive in terms of lives lost and property damage, occurred in the Sea of Japan in an area not known before for seismic or tsunami activity.

In the Hawaiian islands, tsunami have struck repeatedly, causing great loss of life and immense damage to property. Most noteworthy of the recent Hawaiian tsunami is that of 1 April 1946 which inundated and destroyed the city of Hilo, killing 159 people. Other recent tsunami that have hit Hawaii occurred in 1952, 1957, 1960, 1964 and 1975. One of the most devastating recent tsunami was generated by a large earthquake in the Moro Gulf in the Philippines on 16 August 1976. The tsunami waves killed over 8,000 people in Mindanao, leaving 10,000 injured and 90,000 more homeless. In August 1977 a large earthquake in the Lesser Sunda Islands, Indonesia generated a destructive tsunami which killed hundreds of people on Lombok and Sumbawa Islands along the eastern side of the Indian Ocean. Another devastating tsunami occurred on 12 December 1979 in the south-west corner of Colombia destroying several fishing villages, taking the lives of hundreds of people and creating economic chaos in an already economically depressed region of that country. Many more events have occurred in the last twenty years.

Understanding Tsunami Source Mechanism and Potential Terminal Runup

Tsunamis are impulsively generated sea waves by a disturbance at or near the ocean. Earthquakes, submarine volcanic explosions, landslides and the detonation of nuclear devices near the sea can give rise to such destructive sea waves. By far the most destructive tsunamis are generated from large shallow-focus earthquakes with an epicenter or fault line near or in the ocean. Vertical displacements of the earth's crust along the rupture resulting from such earthquakes can generate destructive tsunami waves which can travel across an ocean spreading destruction across their path. Similar displacements of the ocean floor can also be produced by volcanic eruptions and submarine avalanches or landslides. However, these sources are considered as point sources and, although the tsunami waves generated can be very destructive locally, the energy of the waves is rapidly dissipated as they travel across the ocean.

To forecast tsunamis and determine terminal runup and destructiveness, one must be able to evaluate the parameters of the tsunami source mechanism in real time, often from inadequate data. Tsunami source mechanism analysis is difficult given the time constraints of a warning situation. It will suffice to say that forecasting the runup and potential destructiveness of a tsunami at a distant shore will depend greatly on determining the seismic parameters of the source location such as magnitude of the earthquake, its depth, its orientation, the length of the fault line, the size of the crustal displacements, and depth of the water. Refraction and diffraction processes will affect the energy and height of the tsunami waves as they travel across the ocean. These effects must also be determined. Finally, terminal height, run-up, and inundation of the tsunami at a point of impact will depend upon the energy focusing effect, th travel path of the waves, the coastal configuration, and the offshore bathymetry, only to name a few.

Tsunami run-up is the vertical distance between the maximum height reached by the water on shore and the mean-sea-level surface. Contrary to meteorological predictions, tsunami run-up, the final product of earthquake and tsunami investigations is not possible to forecast with a great degree of accuracy. The reason for this inadequacy is that the Tsunami Warning System works in a real time frame of short duration, often with inadequate data and information. Problems of communications and lack of sufficient station density, often complicate the process . Forecasting tsunamis requires adequate understanding of the phenomenon, good and expeditious collection of earthquake and sea level data, and accurate and expeditious assessment and interpretation of this data.

Preparedness and Planning

There is very little that can be done to prevent the occurrence of natural hazards. But while these natural disasters cannot be prevented, their results, such as loss of life and property, can be reduced by proper planning. Government agencies should formulate land-use regulations for a given coastal area with the tsunami risk potential in mind, particularly if such an area is known to have sustained damage in the past. Tsunami hazard perception by the people of a coastal area is necessary in mitigating loss of life and damage to property. Hazard perception by the public is based on a technical understanding of the phenomenon, at least at the basic level, and a behavioral response stemming from that understanding and confidence of the public for the authorities responsible for warning.

Over warning, based on inadequate data on which to base the prediction, often leads to false alarms and lack of compliance with warning and evacuation attempts. Such false alarms result in a loss of faith in the capability of a warning system and result in reluctance to take action in subsequent tsunami events.

Fortunately, forecasting of tsunami in recent years has been quite good and the image of the Tsunami Warning System and its credibility have improved considerably. Forecasting, however, is not an exact science as the phenomenon itself is very complex and data on which the forecast is based may often be inadequate for certain areas of the Pacific.

The International Tsunami Warning System

Following the disaster caused by the tsunami of 1 April 1946 in the Hawaiian Islands and elsewhere a rudimentary warning system was established in 1948 to provide watch and warning information to the civil authorities and various military headquarters in the Hawaiian Islands for dissemination to military bases throughout the Pacific and to islands in the Trust Territories. Beginning in October 1953 warning information was extended to California, Oregon and the State of Washington.

The great destruction caused by the May 1960 Chilean tsunami prompted a large number of countries and territories to Join the TWS. Another catastrophic tsunami generated by the great Alaskan earthquake of 1964 emphasized the need for an International Tsunami Warning System.

In 1965, the United Nations Educational Scientific and Cultural Organization's Intergovernmental Oceanographic Commission accepted the United States' offer to expand its existing Tsunami Center in Honolulu to become the Pacific Tsunami Warning Center (PTWC). Also established was an International Coordination Group (ICG/ITSU) and the International Tsunami Information Center (ITIC) to review and coordinate the activities of the International Tsunami Warning System for the Pacific (ITWS). The Pacific Tsunami Warning System has become the nucleus of a truly international system. Twenty-two nations are now members of ICG/ITSU. Several non-member stations and territories maintain stations for the ITWS. The present system makes use of twenty-four seismic stations, fifty-three tide stations and 101 dissemination points scattered throughout the Pacific Basin under the varying control of the Member States. PTWC in Honolulu, operated by the U.S. National Weather Service, Pacific Region, is the operational Center for the System.

Functioning of the system begins with the detection by any participating seismic observatory of an earthquake of sufficient size to trigger the alarms, set at the threshold of 6.5 on the Richter Scale. PTWC collects the seismic data, locates the earthquake and computes its magnitude. When reports from tide stations show that a tsunami has been generated which poses a threat to the population in part or all of the Pacific, a warning is transmitted to the dissemination agencies for relaying to the public. The agencies then implement predetermined plans to evacuate people from endangered areas. In addition to the International Tsunami Warning System, a number of Regional Warning Systems have been established to warn the population in areas where tsunami frequency is high and where immediate response is necessary. Such regional tsunami warning systems have been established in the Soviet Union, Japan, Alaska and Hawaii.


Pararas-Carayannis George. TSUNAMI: FORECASTING. PREPAREDNESS AND WARNING, Fifteenth Conference on Broadcast Meteorology of the American Meteorological Society, April 9-12, 1985, Honolulu, Hawaii

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