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



George Pararas-Carayannis

(Excerpts from articleS published in Earthquakes and Volcanoes, and in Sea Frontiers. NOTE: Since this article was written a number of changes have taken place. More countries have joined the International Tsunami Warning System and more seismic and tidal stations have been added to the network. Look for Updates)

Awarded a Times Pick by the Los Angeles Times on 8/5/98 Selected by the National Science Teachers Association (NSTA)

Historical Background

Of all natural disasters, tsunamis are among the most terrifying and complex phenomena, responsible for great loss of lives and vast destruction of property. Enormous destruction of coastal communities has taken place throughout the world by such great waves since the beginning of recorded history.

The impact of tsunamis on human societies can be traced back in written history to 1480 BC, when the Minoan civilization in the Eastern Mediterranean was wiped out by great tsunami waves generated by the volcanic explosion of the island of Santorin. In the Pacific Ocean where the majority of these waves have been generated, the historical record, although brief, shows tremendous destruction. In Japan which has one of the most populated coastal regions in the world and a long history of earthquake activity, tsunamis have destroyed entire coastal communities. There is also history of tsunami destruction in Alaska, in Hawaiian Islands, and in South America.

The Need for a Warning System

While most of the destructive tsunamis have occurred in the Pacific Ocean, devastating tsunamis have also occurred in the Atlantic, the Indian Ocean, and in the Mediterranean Sea. In the last 30-40 years there has been tremendous growth and development of the coastal areas in most of the developing or developed Pacific nations. This is the result of population growth and of technological and economic developments that have made the use of the coastal zone more necessary than before. Many of the countries of the Pacific, for example, have populations with natural maritime orientation. For many of these countries foreign trade is a necessity so they maintain major port facilities. Others have extensive ship building facilities, electric plants, refineries, and other important coastal structures. A number of countries throughout the Pacific have now begun important aqua culture industries and canneries. This combination of social and economic factors makes a number of developed and developing countries of the Pacific vulnerable to the threat of tsunamis.

To protect life and property in the Pacific an International Pacific Tsunami Warning System has been organized using an extensive network of seismic and tidal stations, as well as communications, to ensure that the warning information is prompt and accurate. This Pacific Tsunami Warning System is an offspring of a basic U.S. warning system that was initially designed to protect the Hawaiian Islands. The following is a review of the history and evolution of this System.

The U.S. and Other Tsunami Warning Systems

Earlier U.S. System: After the Aleutian tsunami of April 1, 1946 caused major damage and many casualties in the Hawaiian Islands, it was obvious that a means of providing warnings to the population of Hawaii was necessary. This early U.S. Tsunami Warning System was confronted with a number of problems that had to be solved. The Warning System had to detect and rapidly locate earthquakes in the Pacific region, and if one occurred in an area where tsunami generation was possible, to determine quickly whether indeed a tsunami had been generated. Also it was necessary to develop a method for accurate arrival times of the tsunami at various places. Initially a tsunami travel time chart for Honolulu was prepared. Later, travel time charts were also prepared for other stations in the System. For the prototype system a detector was actuated by unusual wave motion of the tsunami to ring an alarm.

Damage to the Scotch Cap lighthouse from the Aleutian tsunami of April, 1946, Umimak Island, Alaska; before and after. (Coast Guard Photos)


Early Methods of Earthquake Measurements and Tsunami Warning: In 1946 photographic methods were still used to record earthquakes because they were simple, practical and precise. Visual recording equipment was needed to be used in conjunction with existing seismographs. In 1947 and 1948 these new instruments were built and installed at three seismic observatories. Later these installations were modified by adding a new electronic amplifier. It included an alarm circuit so that whenever a major earthquake was recorded, an audible and/or visible alarm was tripped, thus insuring prompt observation of every major earthquake. Also a tentative communication plan was prepared utilizing existing communication of the U.S. Armed Forces and of the Civil Aeronautics Administration. The original Tsunami Warning System consisted of three seismological observatories of the Coast and Geodetic Survey at Sitka, College, Tucson, and Honolulu, and tide stations at Attu, Adak, Dutch Harbor, Sitka, Palmyra Island, Midway Island, Johnston Atoll, Hilo, and Honolulu. Honolulu Observatory was made the headquarters of this initial Tsunami Warning System. Its function was to supply tsunami 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 the islands in the United States Trust Territories of the Pacific. Later, in 1953 warning information was also given to the civil defense agencies of California, Oregon, and Washington.

Other countries in the Pacific, such as Japan and USSR had also established rudimentary national warning systems, with the responsibility of warning primarily their own civil defense authorities and protecting their own national interests. These systems had limited data collection capabilities, limited communications within their own national jurisdictions, and limited warning dissemination capability.

International Cooperation

The great destruction caused by the May 1960 Chilean tsunami prompted a large number of countries and territories to join the Pacific TWS, at least by contributing data and information. The great Alaskan earthquake of 1964 generated a devastating tsunami that affected a good part of the Pacific. This tsunami focused additional attention to the need for an International Tsunami Warning System.

Tsunami of May 24, 1960, caused enormous damage at Hilo, Hawaii. (Photograph by Honolulu Advertiser).

In 1965, the United Nations Educational, Scientific, and Cultural Organization's (UNESCO) Intergovernmental Oceanographic Commission (IOC) accepted an offer made by the United States to expand its existing Tsunami Warning Center in Honolulu to become the headquarters of an International Pacific Tsunami Warning System and at the same time accepted the offer of other IOC member countries to integrate their existing facilities and communications into this System. A meeting was held in Honolulu, Hawaii in 1965 establishing the International Tsunami Information Center (ITIC) and an International Coordination Group for the Tsunami Warning System (ICG/ITSU).

ITIC was given the general mandate of mitigating the effects of tsunamis throughout the Pacific by supporting member states of ICG/ITSU in developing and improving preparedness for tsunamis; by monitoring and seeking to improve the Tsunami Warning System for the Pacific; by gathering and disseminating knowledge on tsunamis, by fostering tsunami research; and by bringing to non-member states a knowledge of the Tsunami Warning System and ITIC, and information on how to become participants through IOC/ITSU.

The International Coordination Group, established as a subsidiary body of IOC, meets every two yeas in a member state to coordinate and review the activities of the International Tsunami Warning System (ITWS).

The Pacific Tsunami Warning System

The existing U.S. Warning System was integrated with the Systems of Japan, USSR, Chile, and of other regional centers, and became a truly International Tsunami Warning System. The following twenty-eight nations are now participating members of ITSU in the Pacific : Australia, Canada, Chile, China, Colombia, Cook Islands, Costa Rica, Democratic People's Republic of Korea, Ecuador, Fiji, France, Guatemala, Indonesia, Japan, Mexico, New Zealand, Nicaragua, Peru, Philippines, Republic of Korea, Singapore, Thailand, Federation of Russia, United States of AmericaUSA,and Western Samoa.

Several nonmember states and territories maintain stations for the ITWS. The System makes use of 69 seismic stations, 65 tide stations, and 101 dissemination points scattered throughout the Pacific Basin under the varying control of the member states of ITSU. The Pacific Tsunami Warning Center at Ewa Beach near Honolulu is operated by the U.S. National Weather Service, Pacific Region (see adjacent NOAA diagram).

Also, a program of preparedness has been developed alerting coastal populations, industries, and Civil Defense agencies to respond to tsunami warnings. The International Tsunami Information Center (ITIC) has the responsibility of coordinating public educational programs for each participating country. ITIC works closely with government agencies, private institutions, and Civil Defense authorities, developing sound coastal management policies which include zoning and planning for coastal areas, as well as standard operating procedures in case of an actual event.

The objectives of the Pacific Tsunami Warning System are to detect and locate major earthquakes in the Pacific region as soon as possible, to determine whether they have generated tsunamis, and to provide timely and effective information and warnings to. the population of the Pacific in order to minimize the hazards to life and property.

How the System Works

Functioning of the system begins with the detection of an earthquake which has a magnitude and location that make it potentially tsunamigenic. The earthquake has to be of sufficient magnitude to trigger the alarm attached to the seismograph at the station where it is being recorded. The alarm thresholds are set so that ground vibrations of the amplitude and duration associated with an earthquake of approximate magnitude 6.5 or greater on the Richter scale anywhere in the Pacific region will cause them to sound. This magnitude is below the threshold for issuing watch and warning messages. Personnel at the station immediately interpret their seismograms and send their readings to the Pacific Tsunami Warning Center. Upon receipt of a report from one of the participating seismic observatories or as a consequence of the triggering of their own seismic alarm, PTWC personnel send messages requesting data from the observatories in the system.

Destruction from the 1964 tsunami at Seward, Alaska.

When sufficient data have been received so that the earthquake can be located and the magnitude computed, a decision is made as to further action. If the earthquake is strong enough to cause a tsunami and is located in an area where this is possible, participating tide stations near the epicenter are requested to monitor their tide gauges. Watch bulletins are issued to the dissemination agencies for all earthquakes of magnitude 7 or greater occurring in the Aleutian Islands and all earthquakes of magnitude 7.5 or greater occurring elsewhere in the Pacific. A watch may also be disseminated by the PTWC upon the issuance of warnings by regional warning centers. Since the regional systems use different criteria for their disseminations, a watch may at times be issued for earthquakes with magnitude less than 7.5.

When reports from tide stations show that a tsunami poses a threat to the population in part or all of the Pacific, a warning is transmitted to the dissemination agencies for relay to the public. These agencies then implement plans to evacuate people from endangered areas. If the tide station reports indicate that either a negligible tsunami or no tsunami has been generated, PTWC issues a cancellation.

Capabilities and Limitations of the System

A tsunami originates in or near the epicentral area of the earthquake that creates it. It propagates outward in all directions at a speed that depends on ocean depths. In the deep ocean, the speed may exceed 600 kms per hour; thus, the need for rapid data handling and communication becomes obvious. Because of the time spent in collecting seismic and tidal data, the warnings issued by PTWC cannot protect areas against local tsunamis in the first hour after generation; for this purpose, regional warning systems have been established in some areas.

The regional systems generally have data from a number of seismic and tide stations telemetered to a central headquarters. Nearby earthquakes are located, usually in 15 minutes or less, and a warning based on seismological evidence is released to the population of the area. Since the warning is issued on the basis of seismic data alone, watches or even warnings will occasionally be issued when tsunamis have not been generated. Since they are issued only to a restricted area and confirmation of the existence or nonexistence of a tsunami is rapidly obtained, dislocations of populations are minimized. To limit the number of agencies to be contacted, warnings are generally issued to only one agency in each country, territory, or administrative area.

Dissemination agencies have the continuing responsibility for educating the public concerning the dangers of tsunamis and for developing safety measures that must be taken to avoid loss of life and to reduce property damage. The agencies are encouraged to develop emergency plans for all threatened localities, clearly delineating areas of possible inundation. Evacuation routes should be designated, safe areas marked, and the amount of advance warning to insure evacuation from danger areas determined.

Present and Planned Improvements

A general operational concept is presently being developed for the International Tsunami Warning System using updated technology and instrumentation. The objective is to reduce the time needed to evaluate the tsunami hazard, make decisions, and disseminate the warnings, on a Pacific-wide or a regional basis. The new system is using a large network of shore-based seismic and tsunami sensors transmitting real-time data to the International Tsunami Warning Center (ITWC) in Honolulu, making use of synchronous meteorological satellites for communication relay.

Additional refinements to the operating system will include offshore tsunami bottom sensors using crystal pressure-transducers, acoustic or wire links with existing buoy systems, data microprocessors, and data links via geostationary satellites between shore installations and the ITWC. Both the offshore and the coastal tsunami sensors will be continuously-recording, event-activated, or activated on demand. The prototypes for coastal installation are complete, tested, and working. Additional work is needed in the adaptation of microcomputers, power supplies, acoustic links with buoys, and the housing of the offshore tsunami sensors. A unique data-processing interphase system has been developed for the ITWC in Honolulu using a multi task computer system to handle increased data loads available through the synchronous satellites and other data networks. The new technology is resulting in a more efficient International Tsunami Warning System.

Finally, the International Tsunami Warning System is one of the most successful international programs ever undertaken involving a multitude of nations with the direct responsibility of mitigating the effects of tsunamis, the saving of lives, and the preservation of property. It is an effective operational program with a direct humanitarian objective-the protection of human lives in the Pacific Ocean coastal areas. The system has been made possible by the generous contributions and participation of the Community of Nations of the Pacific, by IOC's involvement, and by the active and effective coordination of ITIC and of the International Coordination Group.


Pararas-Carayannis, G. 1977. "The International Tsunami Warning System", Sea Frontiers, Vol. 23, No. 1, 1977, pp.20-7.

Pararas-Carayannis, G. 1986, The Pacific Tsunami Warning System, Earthquakes and Volcanoes, Vol. 18, No. 3, , p. 122-130, 1986.


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