2000 B.C. - 2007
Table of Contents:
The NGDC tsunami database is a listing of historical tsunami source events and runup locations throughout the world that range in date from 2000 B.C. to the present. The events were gathered from scientific and scholarly sources, regional and worldwide catalogs, tide gauge reports, individual event reports, and unpublished works. There are currently over 1,700 source events in the database with event validities >0 (0=erroneous entry). The global distribution of these events is 71% Pacific Ocean, 11% Mediterranean Sea, 9% Atlantic Ocean and Caribbean Sea, 6% Indian Ocean, and 3% Black Sea. There are over 9,600 runup locations where tsunami effects were observed. The global distribution of these locations is 82% Pacific Ocean, 6% Atlantic Ocean and Caribbean Sea, 3% Mediterranean, 9% Indian Ocean, and <1% in the Red Sea and Black Sea.
Tsunamis, commonly called seismic sea waves--or incorrectly, tidal
waves--have been responsible for at least 745 fatalities and over 200
hundred million dollars in property damage in the United States and
its territories. These events are somewhat rare. Major tsunamis occur
in the Pacific Ocean region only about once per decade. Therefore, it
is important to learn as much as possible from the relatively short
"Tsunami" is a Japanese word meaning "harbor wave." It is a water
wave or a series of waves generated by an impulsive vertical
displacement of the surface of the ocean or other body of water. Other
terms for "tsunami" found in the literature include: seismic sea wave,
Flutwellen, vloedgolven, raz de mare, vagues sismique, maremoto,
and, incorrectly, tidal wave. The term "tidal wave" is frequently used
in the older literature and in popular accounts, but is now considered
incorrect. Tides are produced by the gravitational attraction of the sun
and moon and occur predictably with twelve hour periods. The effects
of a tsunami may be increased or decreased depending on the level of
the tide, but otherwise the two phenomena are independent.
Although there are warning systems for tsunamis occurring around the
Pacific, including local and regional warning systems in Hawaii and
Alaska, the risks from future tsunamis are still not fully known. Some
events, such as that in Prince William Sound, Alaska, in March 1964,
can be devastating over large distances. Even over short distances
along a coast, the heights of a tsunami wave will vary considerably.
An important part of the risk assessment is to gain a clearer
understanding of the effects of past tsunamis.
Worldwide Occurrence of Tsunamis
Tsunamis have been reported since ancient times. They have been
documented extensively, especially in Japan and the Mediterranean
areas. The first recorded tsunami occurred off the coast of Syria in
2000 B.C. Since 1900 (the beginning of instrumentally located
earthquakes), most tsunamis have been generated in Japan, Peru,
Chile, New Guinea and the Solomon Islands. However, the only
regions that have generated remote-source tsunamis affecting the
entire Pacific Basin are the Kamchatka Peninsula, the Aleutian
Islands, the Gulf of Alaska, and the coast of South America. Hawaii,
because of its location in the center of the Pacific Basin, has
experienced tsunamis generated in all parts of the Pacific.
The Mediterranean and Caribbean Seas both have small subduction
zones, and have histories of locally destructive tsunamis. Only a few
tsunamis have been generated in the Atlantic Ocean. In
the Atlantic Ocean, there are no subduction zones at the edges of plate
boundaries to spawn such waves except small subduction zones under
the Caribbean and Scotia arcs.
In the Indian Ocean, the
Indo-Australian plate is being subducted beneath the Eurasian plate at
its east margin. On December 26, 2004, an earthquake off the coast of northern Sumatra generated a tsunami that was recorded nearly world-wide and killed more people than any other tsunami in recorded history. More than 297,248 people were either killed or listed as missing and presumed dead and 1,126,900 were displaced by the earthquake and subsequent tsunami. The estimated economic losses exceed $10 billion. The devastating megathrust earthquake of December 26th, 2004 occurred on the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate. The India plate begins its descent into the mantle at the Sunda trench which lies to the west of the earthquake's epicenter. The trench is the surface expression of the plate interface between the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast.
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Most tsunamis are caused by a rapid vertical movement along a break
in the Earth's crust (i.e., their origin is tectonic). A tsunami is
generated when a large mass of earth on the bottom of the ocean drops
or rises, thereby displacing the column of water directly above it. This
type of displacement commonly occurs in large subduction zones,
where the collision of two tectonic plates causes the oceanic plate to
dip beneath the continental plate to form deep ocean trenches. Most
Subduction occurs along most of the island arcs and coastal areas of
the Pacific, the notable exception being the west coast of the
United States and Canada. Movement along the faults there is largely
strike-slip, having little vertical displacement, and the movement produces
few local tsunamis.
Volcanoes have generated significant tsunamis with death tolls as
large as 30,000 people from a single event. Roughly one fourth of the
deaths occurring during volcanic eruptions where tsunamis were
generated, were the result of the tsunami rather than the volcano. A
tsunami is an effective transmitter of energy to areas outside the reach
of the volcanic eruption itself. The most efficient methods of tsunami
generation by volcanoes include disruption of a body of water by the
collapse of all or part of the volcanic edifice, subsidence, an
accompanying or preceding the eruption. Roughly one-half of all
volcanic tsunamis are generated at calderas or at cones within
calderas. Submarine eruptions may also cause minor tsunamis.
Locally destructive tsunamis may be generated by subaerial and
submarine landslides into bays or lakes. Lituya Bay, Alaska, has been
the site of several landslide-generated tsunamis, including one in
1958 that produced a splash wave that removed trees to a height of
525 m. It also caused a tsunami of at least 50 m in the bay. The 1964
Prince William Sound earthquake triggered at least four submarine
landslides, which accounted for 71 to 82 of the 106 fatalities
in Alaska for the 1964 event. However, it is tectonic
earthquake-generated tsunamis (those produced by a major deformation of
Earth's crust) that may affect the entire Pacific Basin.
Other possible but less efficient methods of tsunami generation
include: strong oscillations of the bottom of the ocean, or
transmission of energy to a column of water from a seismic impulse
(e.g., a deep-focus earthquake that has no surface rupture);
transmission of energy from a horizontal seismic impulse to the water
column through a vertical or inclined wall such as a bathymetric
ridge; strong turbidity currents; underwater and above-water
explosions. Several mechanisms commonly are involved in the
generation of a tsunami (e.g., vertical movement of the crust by a
seismic impulse or an earthquake, and a submarine landslide).
Our knowledge of tsunami generation is incomplete, because the
generation phenomena has not been observed nor measured directly.
However, studies of tsunami data suggest that the size of a tsunami
is directly related to: the shape of the rupture zone, the rate of displacement and sense of
motion of the ocean-floor in the source (epicentral) area, the amount
of displacement of the rupture zone, and the depth of the water in the
It is also observed that long-period tsunamis are generated by
large-magnitude earthquakes associated with seafloor deformation of the
continental shelf; while, shorter period tsunamis are generated by
smaller magnitude earthquakes associated with seafloor deformation
in deeper water beyond the continental shelf.
Once the energy from an undersea disturbance has been transmitted to
the column of water, the wave can propagate outward from the source
at a speed of more than 1,000 km per hour depending on the depth of
the water. Because the height of the long-period waves in the open
ocean is commonly 1 m or less and their wavelength is hundreds of
kilometers, they pass unnoticed by observers in ships or planes in the
velocity of its waves is reduced, and the height of each wave
increases. The waves pile up on shore especially in the region of the
earthquake source, producing a "local tsunami." Some dramatic
examples of such local tsunamis include those generated by landslides
or by volcanic eruptions, which have caused "runup" heights of 30 to
50 m in some coastal areas.
"Runup" is the maximum height of the water observed above a
reference sea level. Two other terms may be determined from the
runup value: (1) tsunami magnitude, which is defined (Iida and
others, 1967) as
- m = log2H
and (2) tsunami intensity, which is defined (Soloviev and Go,
- I = log2(21/2 * H),
where H in both equations is the maximum runup height of the wave.
If the energy produced by the generating disturbance is sufficiently
large, such as that released by a major deformation of the crust in a
trench area, the resulting tsunami wave may cross the open ocean and
emerge as a destructive wave many thousands of kilometers from its
source. The severity of a tsunami of this type--called a
"remote-observed and perhaps cause damage throughout the Pacific Ocean
Basin (e.g., the Chile tsunami of May 1960).
Radiation of a remote-source tsunami from the focus of an earthquake
is directional, depending on the geometry of the seafloor in the source
region. The source region for major tectonic earthquakes is usually
elliptical, and the major axis is as much as 600 km long and
corresponds to the activated part of the fault. The major part of the
tsunami energy is transmitted at right angles to the direction of the
major axis, both toward the near shore and along a great circle path
toward the shore on the opposite side of the ocean. Thus, tsunamis in
Chile have severe impact on Japan; and those in the Gulf of Alaska on
the west coast of North America. Hawaii, which lies in the central
Pacific Basin, is vulnerable to remote-source tsunamis generated both
in the North Pacific and along the coast of South America.
The velocity (V) of a tsunami in the open ocean is expressed as the
product of the square root of the depth of the water (d) and the
acceleration of the force of gravity (g).
- V = (dg)1/2
Because the speed of the tsunami depends on the depth of the ocean
basin, the waves decrease in speed as they reach shallower
wavelength is shortened, the energy within each wave is crowded into
progressively less water, increasing the height of the wave. The
tsunami may increase in height from 1 m in the open ocean to more
than 20 m during runup. Also, if underwater ridges are present, they
may act as collecting lenses and further intensify the tsunami.
If the tsunami encounters a coastal scarp, the height of its waves
increases. Because the long-period wave can bend around obstacles,
the tsunami can enter bays and gulfs having the most intricate shapes.
Experience has shown that wave heights increase in bays that narrow
from the entrance to the head, but decrease in bays that have narrow
entrances. Shores of islands protected by coral reefs commonly
receive less energy than unprotected coastlines lying in the direct path
of an approaching tsunami. Islands in a group may "shadow" one
another reducing the tsunami effect. Small islands may experience
reduced runup as the tsunami waves may refract around them.
A tsunami wave may break on the beach, appear as flooding, or form
a "bore"(violent rush of water with an abrupt front) as it moves up a
river or stream. When the trough of the wave arrives first, the water
level drops rapidly. Where this occurs the harbor or offshore area
may be drained of its water, exposing sea life and ocean bottom. This
phenomenon may be the only warning to residents that a large
tsunami is approaching. Fatalities have occurred where people have
tried to take advantage of this situation to gather fish or explore the
strange landscape. The wave returns to cover the exposed coastline
faster than the people can run. Although there may be an interval of
minutes--or perhaps an hour--between the arrival of waves, the
second, third, or later waves can be more destructive than the first.
Residents returning too soon to the waterfront, assuming that the
worst has past, represent another kind of preventable fatalities.
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(from Introduction to Catalog of Significant Earthquake)
Erroneous statistical conclusions can be drawn from the
numbers of earthquakes taken from Catalog of Significant Earthquakes,
2150 B.C. to the present. The reporting of large or destructive earthquakes
is not homogeneous in space or time, particularly for periods prior to
the 1900s. Because this publication mainly lists those earthquakes that
have caused death or damage, the number of earthquake reports is dependent
on the written history available for a particular region, as well as on
the rate of development of population centers and related structures.
Therefore, it is misleading to use the numbers of significant earthquakes
in that publication to suggest statistically that there has been an
increase in worldwide seismic activity since 1900 or for any time period.
that "apparent" increase in activity:
Instrumental seismology is a young science. The first calibrated
instruments to measure seismic waves traveling through the earth did not
appear until the late 1800s. At that time, seismologists became aware of
the vast numbers of earthquakes occurring throughout the world, but
because of the insensitivity of their instruments they were able to
locate only the large magnitude events.
The 1960s saw two major advances. First, a network of seismological
observatories, the Worldwide Standardized Seismograph Network (WWSSN),
was installed by the United States Government, principally
to monitor underground nuclear tests. These sensitive instruments could
detect and identify earthquakes anywhere in the world from about
Second computers became available in the late 1960s. Computers allowed
seismologists to leave inaccurate and cumbersome graphical methods of
locating earthquakes, and to process the increasing volume of new network
data more rapidly than ever before. Prior to 1962, only hundreds of
earthquake epicenters were determined each year by Government and academic
institutions, but the number increased to the thousands using computerized
location methods. In some special local studies, more than 100,000
earthquakes per year were identified and located.
In summary, using the data in Catalog of Significant Earthquakes,
2150 B.C. to the present to suggest that there has been an increase in
worldwide earthquake activity is misleading and erroneous. The above
observations and reporting factors must also be considered when making
statistical studies based on that historical data report.
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Uncertainties in the Significant Earthquake and Tsunami Databases
(from Introduction to Catalog of Significant Earthquake)
The same problems that can lead to erroneous statistics
discussed in the Caveat, also introduce uncertainties
in the earthquake and tsunami databases for
events prior to the late 1800s, and in some areas for events prior to the
installation of the WWSSN in 1962. Before the invention of seismographs
in the late 1800s magnitudes, times and locations of earthquakes
and tsunami sources were
determined from descriptions of earthquake damage and tsunami effects.
Earthquake epicenters and tsunami source locations may have been assigned
to the wrong places when the names of localitieis were incorrectly
transcribed or when some localities had identical or very similar names.
Errors may have also been introduced when the local times of earthquakes
and tsunami reports were incorrectly converted to Universal Coordinated Time
Earthquake and tsunami events can also be listed twice when the
dates are recorded in different sources according to the Julian or the
As a result, the earthquake and tsunami databases may include listings
of events on different dates that are actually descriptions of the same
event. For a more complete discussion of these errors
please see Historical Seismograms and Earthquakes of the World,
edited by W.H.K. Lee, H. Meyers and K. Shimzaki, 1988, Academic
Press, Inc., San Diego, California,
The tsunami database may also include errors that are unique to that database.
One of the most important measurements associated with a tsunami event is the maximum
runup height or water height reached above sea level in meters. Unfortunately, it is
not always clear which reference level was used. The tsunami database also includes
locations where the tsunami was observed, called runup locations. The same problem that
occurs when identifying earthquake epicenters can occur when assigning runup locations,
where the names of localities were incorrectly transcribed or where some localities had
identical or very similar names. In addition, names of locations can change over time
adding to the possibility of errors. If tsunami arrival and travel times are available
for specific runup locations, they are included in the database. These data are valuable
in verifying tsunami travel time models. The definition used in this database is the
arrival or travel time of the first wave that arrives at a runup location. The first wave
may not have been the largest wave, therefore the travel time reported in the original
source may have been the second or third wave.
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