Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters, Tsunamis of the 21st Century - by Dr. George Pararas Carayannis


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



George Pararas-Carayannis

Excerpts from a paper presented at the Second International Tsunami Workshop on the Technical Aspects of Tsunami Warning Systems, Tsunami Analysis, Preparedness, Observation and Instrumentation. Novosibirsk, USSR, 4-5 August 1989.

Also published in Intergovernmental Oceanographic Commission-UNESCO. Workshop Report No. 58

Copyright © 1989. All Rights Reserved


Tsunamis recur with frequencies of short, medium, long, or super-long cycles. Most are generated by earthquakes, although volcanic eruptions, rockfalls, landslides and other impulsive sources can also generate them. Each region of the world appears to have its own cycle and pattern in generating tsunamis. The majority of events are usually small. However some tsunamis may be highly destructive locally or at great distances across an entire ocean.

In certain very active tectonic regions, particularly in regions of subduction, large earthquakes occur with frequency. In such regions, tsunamis usually follow similar recurrence patterns as those of the large earthquakes. However, in certain other tectonic regions where large earthquakes may be infrequent, tsunami recurrence cycles are irregular, intermittent and of varying periodicity. Events may occur decades or even hundreds of years apart. For events that occur hundreds of years apart, there is no way of establishing periodicity other than through the interpretation of geological and paleontological data. Making accurate predictions as to when exactly destructive tsunamis will occur in the future, is not possible. However, given the time window of a century - and having the benefit of historical information and the knowledge of ongoing tectonic processes on our planet - we can certainly indicate with relative accuracy the locations where small and great tsunamis can be expected in the future. Such information may useful for purposes of tsunami risk assessment, disaster awareness and for overall preparedness.

The ability to forecast or predict tsunamis with any degree of accuracy is limited. Long term tsunami prediction is based primarily on statistical methods of earthquake prediction in identifuing seismic gaps. Medium-term prediction is also based on statistical recurrence frequency, but it is also of limited value. Overall statistic probabilities are of limited use for forecasting purposes - except for events that follow yearly or seasonal cycles - as wheather phenomena for example.

Destructive tsunamis do not always occur in seismic-gap regions that have been clearly identified as such. For example, the 1975 tsunami in the Philippines, the 1979 tsunami in Colombia, and the 1983 tsunami in the Sea of Japan, were all local events that occurred unexpectedly. No one had suspected seismic gaps or build-up of stresses. These regions of the world were not actively monitored. No tsunami warnings were issued for these events that could have been of any value to the threatened population. Thus many lives, were lost. However a review of historical events and an understanding of tectonic processes could have eliminated the surprise element when these events occurred. There had been no destructive tsunamis in these areas in recent times, but there had been several in the distant past. History of disasters repeats itself. A warning could have been issued based on the earthquake parameters alone or the knowledge of past events.

There are many other limitations in making prediction as to where and when destructive tsunamis may strike. However, a real time prediction of a tsunami can be made on the basis of seismic parameters after an earthquake has occurred in an area that had been impacted in the past. Such short-term, real-time predictions can be made and tsunami warnings can be issued for coastal regions that are about one to one and a half hour away from the tsunami generating source. However, it is extremely difficult to warn, in a timely fashion, coastal areas that are very close to the tsunami generating source. The tsunami may only take a few minutes to reach the nearest shore. In recent times, refinements have been made to cut down the time of evaluating such events and in disseminating local warnings. Regional Tsunami Warning Centers have been established that can now issue warnings withing a few minutes after tsunami generation for their immediate areas of their jurisdiction. However, the evaluation and the warnings are often based on nothing more than vague earthquake parameters and the region's known tsunamigenic history.

The following analysis is simply an overview of where destructive local regional and ocean-wide tsunamis can be reasonably expected in the 21st Century and subsequently. This overview is based on historical information and known tectonic processes and interactions. No attempt is made to explain the mechanisms of the interactions.

Difficulties and Limitations in Determining When and Where Future Tsunamis May Strike?

Although most of the large tsunamigenic earthquakes occur in geological cycles which may be considered regular or rhythmical, conditions that are exogenous or random often cause time variations in their recurrence. This is what makes their prediction difficult. Because of the scarcity of historical data for large tsunamigenic earthquakes, only statistical methods of extremes have been used to obtain statistical recurrence values. These are of limited value because the confidence limits are low. Similarly, because the epicenters of most of the large tsunamigenic earthquakes are in the ocean, it is often difficult to measure other geophysical and geochemical precursory phenomena that would give clues as to event recurrence. However, based on currently available information, each known tsunamigenic region of the world can be assigned its own recurrence frequency or recurrence cycle - if studied and documented extensively. Even though each destructive tsunami has its own unique source pattern and its own time and impact variables, certain general principles seem to apply to most of them, which will be simply referred to here by the author as abiding by the proposed "law of tsunami disaster cycles".

A Statistical Approach To Tsunami Event Prediction - Inadequacy of Statistical Methods and of the Seismic Tsunami Gap Theory.

As mentioned, a statistical approach - such as the seismic gap theory - may not be valid for tsunami predictions. In this author's opinion, the 30-year time interval - which is the criterion for establishing a seismic gap - may be too short of an interval for predictions of destructive tsunamis, particularly for certain geographical regions of the world. For example, numerous large earthquakes have occurred along the Azores Gibraltar Fault Zone. However, there has been no recurrence of the great Lisbon earthquake and tsunami of 1755.

What is proposed here is a new theory which is named the "tsunami gap theory." The criteria for the development of the tsunami gap designations will not be uniform, but will differ in accordance to the tectonic characteristics of each region. According to this approach, the time path of variables of each future tsunami could be established, or at least estimated statistically for each potential tsunamigenic area, by using both historical and geophysical data. The same historical and geophysical criteria could be projected to form predictive schemes relating to other seismic tsunami source parameters, and for expected near and far-field tsunami effects - the latter further determined by analysis of numerous factors at each terminal point. For example, for vulnerable locations such as Hilo, Hawaii, there is more than adequate information on historical tsunamis and their runups, on bottom bathymetry, on geomorphological configuration of the coastaline, on land topography and on frictional parameters. This information is already incorporated in the evaluation process in predicting the height, terminal velocity and potential runup of any tsunami from any direction of approach - regardless of the source region. Such specific tsunami risk analysis would be required for other critical coastlines vulnerable to tsunamis of both local and distant origin.


This type of historical, statistical, geophysical, oceanographic and engineering analysis, if properly executed, can establish tsunami gap regions and can lead to better forecasts of future destructive events and their impact to near or distant shores. The centerpiece of the proposed approach is named "historical tsunami determinism." It is much more than collecting and cataloguing historical tsunami information. The basic premise of the proposed process is that tsunamis follow certain patterns, although these are not uniform for all regions of the world. A simple qualitative historical information database is not sufficient. For each tsunamigenic region, the database must include accurate quantitative measurements and cataloguing of all meaningful tsunami disaster parameters, including seismic parameters, and geophysical precursory phenomena. Furthermore the database

This may be somewhat difficult to do for all regions of the world, but it should be definetely and we may have to establish a new methodology for doing it. Also it will require the development of an extensive tsunami data base which should include, not only historical information, but other extensive data and catalogues as for example - data on focal mechanisms, power spectra, seismic moments of previous seismic events on specific broadband seismic signatures. Developing such historical and geophysical data bases would require a great deal of effort. However, we could standardize the development of such data bases, and we could agree conceptually on the methodology and the development of such historical tsunami determinism, and we could integrate this knowledge into real-time operational assessment of the tsunami risk for warning purposes.

Forecasting The Tsunamis of the 21st Century

There should not have been surprise by the occurrence of the 1975 Philippine tsunami or the 1979 Colombian tsunami, or the 1983 Sea of Japan tsunami. There is historical and geologic precedents for all these events, and their occurrence should have been expected. Similarly, source and impact regions of future tsunamis could be forecasted for the remainder of this century and for the 21st Century, by utilizing these proposed extensive historical and geophysical databases.

Forecasting of future tsunamis on the medium or longer term may be possible. Just as with earthquakes, prolonged periods of quiescence of a region that has been historically tsunamigenic (using the tsunami gap hypothesis and criteria) may be signaling the eventual occurrence of another destructive tsunami. Many such areas exist presently in the Pacific and elsewhere, and the location of these regions can be identified. If we develop the proper criteria of historic tsunami determinism, we can also assign a time frame for tsunami recurrence. This can be done not only for areas of established seismic gaps but for areas where seismic gaps have not been identified, or for which a different recurrence time frequency applies.

The data exists, but its proper analysis has not been undertaken. A total of 482 tsunamis have been reported in the 20th Century alone, with at least 133 having a runup greater than 1.5 meters. We know that Japan, the West Coast of South America, Alaska, the Aleutian Islands, Kamchatka, and the Kuril Islands are potential tsunami generating areas. We know that these are the boundaries of major tectonic plates. But what about all the other subplates of the inland seas that have produced also the big destructive tsunamis and for which we have not established seismic gaps?

Where in the Pacific Ocean can we expect the big tsunamis in the 21st Century other than the areas mentioned? Let us be more specific. There are many tsunamigenic regions that have shown high density of seismic energy release and where large future tsunamis can be expected. For example, one such area is a segment of the Peruvian coastal region between 8.5° S and 14° S. This is a region of extremely high seismic energy release and site of large but infrequent historical tsunamis. Other parts of the South American seismic belt are tsunami gap regions and these regions in the 17th, 18th and 19th Centuries produced several destructive tsunamis, destroying such towns in Chile as Arica, Antofagasta and Valparaiso. There is also a great potential for another destructive tsunami on the Pacific side of Colombia, in the vicinity of the State of Narino. The west coast of Mexico can be expected to experience larger tsunamis. Large destructive tsunamis can be expected again in the Moro Gulf in the Philippines, in the Celebes and Sulu Sea, in the Java Sea and elsewhere in the South West Pacific.

A lot can be said about the potential of such future tsunamis, but to make reasonable predictions about the time and place of future events, the criteria of the proposed historical determinism must be utilized. These criteria have not been as yet developed and I propose that we develop them. As a starting point, we need to develop a uniform and standardized program of tsunami, seismic and geologic data collection. A wealth of such data already exists but this data is not properly organized, is not uniformly collected, and of course it is not readily available. Therefore, standards must be established for the collection of such data and a tsunami data base must be organized on a regional basis initially, and shared on a global scale at a later time. Finally, the methodology of historical tsunami determinism as I described earlier for real-time operational use must be established.


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