Test Glossary Import

Tsunami occurring prior to the historical record or for which there are no written observations.  

Paleotsunami research is based primarily on the identification, mapping, and dating of tsunami deposits found in coastal areas, and their correlation with similar sediments found elsewhere locally, regionally, or across ocean basins. In one instance, the research has led to a new concern for the possible future occurrence of great earthquakes and tsunamis along the northwest coast of North America. In another instance, the record of tsunamis in the Kuril-Kamchatka region is being extended much further back in time. As work in this field continues it may provide a significant amount of new information about past tsunamis to aid in the assessment of the tsunami hazard.

Tsunamis are relatively rare events and most of their evidence is perishable. Therefore, it is very important that reconnaissance surveys be organized and carried out quickly and thoroughly after each tsunami occurs, to collect detailed data valuable for hazard assessment, model validation, and other aspects of tsunami mitigation. 

Since the early 1990s, post-tsunami reconnaissance surveys have been organized following each major destructive tsunami to make measurements of runups and inundation limits, to collect associated data from eyewitnesses such as the number of waves, arrival time of waves, and which wave was the largest, and to assess human response to tsunami danger. The surveys have been organized on an ad-hoc basis, facilitated and coordinated by the IOC and ITIC working with the affected country, and conducted by international academic tsunami researchers (International Tsunami Survey Team, ITST). The IOC-ITST Post-tsunami Survey Field Guide (Manuals and Guides 37, 1998, 2nd Edition 2014, IOC/2014/MG/37) provides a flexible framework for undertaking surveys, their guiding principles and protocols data types, and observations to be taken to standardize data collection.

After a major tsunami, physical oceanographers, social scientists and engineers conduct post-tsunami surveys to collect information. These data, including runup, flow depth, and inundation, deformation, scour, building and structural impact, wave arrival descriptions, and social impact, are important for designing better mitigation to reduce the impacts of tsunami on life and property. Photo courtesy of Philip Liu, Cornell University.

ITST measuring tsunami runup using laser rangefinder in El Salvador, 2012. Photo courtesy of ITIC.

A hypothetical water level (exclusive of wave runup from normal wind-generated waves) that might result from the most severe combination of hydrometeorological, geoseismic and other geophysical factors that is considered reasonably possible in the region involved, with each of these factors considered as affecting the locality in a maximum manner. This level represents the physical response of a body of water to maximum applied phenomena such as hurricanes, moving squall lines, other cyclonic meteorological events, tsunamis, and astronomical tide combined with maximum probable ambient hydrological conditions such as wave level with virtually no risk of being exceeded.

Probabilistic Tsunami Hazard Assessment. An assessment of the probability that a tsunami will reach, or exceed, a given size within a specified interval of time at a particular location. The tsunami size may be measured in various ways, such as: run-up height, flow depth, or tsunami height at the coast. Usually a PTHA would provide probabilities for a range of different time spans, for example from 50 to 2500 years. The assessment may cover a single location, a stretch of coastline, or an area of land (if inundation is included). See also ‘Tsunami Hazard Assessment’ which provides information on some of the techniques that may be used to make a PTHA.