FIRST
TSUNAMI SYMPOSIUM
May 25-27, 1999
East-West
Center, University of Hawaii
Honolulu,
Hawaii, USA
PROGRAM
AND ABSTRACTS
MAY
25, 1999, 8:30 Morning
OPENING CEREMONIES - George Curtis, President The Tsunami Society
ASTEROID MEGA-TSUNAMIS
- Morning Session
9:00 - Comet and Asteroid Hazards: - Threat and Mitigation -
J. Solem, LANL
9:30 - Asteroid Tsunami Project at Los Alamos - J. Hills, and
P. Goda LANL
10:00 - Refreshment Break
10:30 - High Fidelity Computational Simulations of Asteroid and
Comet Impacts - D. Crawford, SNL
11:00 - Impact Tsunami: A Hazard Assessment - S. Ward, E. Asphaug,
UC SC
11:30 - Animations of Asteroid Tsunami Inundations - C. Mader,
MCC
OTHER MEGA-TSUNAMIS
- Afternoon Session
1:00 - The 1958 Lituya Bay Mega-Tsunami - C. Mader, LANL
1:30 - Analysis of Mechanism of Lituya Bay Tsunami - G. Pararas-Carayannis
2:00 - Did a ``Giant Wave'' Strike Lanai? - B. Keating, A. Felton,
HIGP
2:30 - Refreshment Break
RECENT TSUNAMI DISASTERS
- 5/25/99 Afternoon Session - G. Fryer, Chairman
3:00 - The 1998 New Guinea Tsunami - C. Synolakis, USC (no abstract)
3:30 - 1994 Skagway Landslide Tsunami - B. Campbell, D. Nottingham,
PN and D
4:00 - 1983 - 2000 Global Tsunami Catalogue - J. Lander, K. O'Loughlin,
L. Whiteside, CIRES
MAY 26, 1999
TSUNAMI WARNING CENTERS
- 5/26/99 Morning Session - R. Hagermeyer, Chairman
8:30 - Pacific Tsunami Warning Center - C. McCreery
9:00 - The U.S. West Coast and Alaska Tsunami Warning Center
- T. Sokolowski
9:30 - Japanese Tsunami Warning System - A. Furumoto, H. Tatehata,
A. Morioka
10:00 - Refreshment Break
10:20 - Caribbean Tsunami and Warning System Status - J. Lander,
K. O'Loughlin, L. Whiteside, CIRES
10:45 - Tsunami Risk for Australia - J. Rynn and J. Davidson,
CERA
11:10 - Landslide Tsunami: Generation, Detection and Warning
- S. I. Iwasaki, S. Sakata, Tsukuba, Japan
1:35 - Tsunami Warning in Central America - M. Fernandez , CIGEFI,
Costa Rica J. Havskov, K. Atakan, Univ. of Bergen, Norway
PTWC Tour - 5/26/99 Afternoon
BANQUET 6:00 p.m.- Doak Cox - Speaker
MAY 27, 1999
TSUNAMI CIVIL DEFENSE
PROJECTS - 5/27/99 Morning - D. Cox, Chairman
8:30 - Hawaii CD Local Tsunami Problem - D. Walker, UH
9:00 - Tsunami Warning Systems in U.S.A. - A. Furumoto, Honolulu,
HI
9:30 - Finite Element Modeling of Potential Cascadia Subduction
Zone Tsunamis - E. Myers, A. Baptista, G. Priest, OGI
10:00 - Refreshment Break
10:30 - Cascadia Paleotsunamis - I. Hutchinson, P. Bobrowsky,
J. Clague and R. Mathewes, SFU Canada
11:00 - Tsunami Mitigation for the City of Suva, Fiji - J. Rynn,
G. Prasad, A. Kaloumaira, CERA
11:30 - Pacific Tsunami Museum - W. Dudley, UH
HISTORICAL TSUNAMIS
- 5/27/99 Afternoon - M. Blackford, Chairman
1:00 - Tsunamis on the Coast Lines of India - T. S. Murty, lBA
Canada
1:30 - Paleotsunami Evidence from the Australian Continent -
J. Nott, JCU
2:00 - Tsunamis in Greece - D. Domeny Howes - Coventry Univ.
2:30 - Methods of Calculation of Tsunami Risk - G. Curtis, E.
Pelinovsky, UH
3:00 - Refreshment Break
3:15 - TSUNAMI SOCIETY
ANNUAL MEETING
ABSTRACTS
TSUNAMI
SYMPOSIUM
May 25-27, 1999
East-West
Center, University of Hawaii
Honolulu,
Hawaii, USA
COMET AND
ASTEROID HAZARDS: THREAT AND MITIGATION
Johndale C. Solem
Los Alamos National Laboratory
Los Alamos, New Mexico USA
The magnitude of the threat posed by comets or asteroids that
might collide with the Earth will be described. While the probability
of collision is small, the effects including tsunamis could be
devastating, suggesting that it should be carefully considered
in relation to other natural disasters. It is one of the few
natural disasters that could be averted by technical means. Although
many more complex schemes are possible, the most cost-effective
and the only currently-available means of disruption (deflection
or pulverization) is anuclear explosive. The optimal tactics
for terminal intercept and remote-interdiction scenarios will
be described. The optimal mass ratio of an interceptor rocket
carrying a nuclear explosive depends mainly on the ratio of the
exhaust velocity to the object closing velocity. Nuclear explosives
can be employed in three different modes depending on their location
at detonation: (1) buried below the object's surface by a penetrating
vehicle: (2) detonated at the object's surface; or (3) detonated
some distance above the surface. A model for gravitationally
bound objects will be used to obtain the maximum non-fracturing
deflection speed for a variety of object sizes and structures.
For a single engagement, we conclude that the non-fracturing
deflection speed obtainable with a stand-off device is about
four times the speed obtainable with a surface-burst device.
Furthermore, the non-fracturing deflection speed is somewhat
dependent on the number of competent components of the object.Generalizations
indicate: (1) asteroids more than 3 km in diameter can be the
most efficiently deflected with a surface burst; (2) asteroids
as small as half km in diameter can be effectively deflected
with a stand-off device; (3) smaller asteroids are best pulverized.
THE ASTEROID
TSUNAMI PROJECT AT LOS ALAMOS
Jack G. Hills and M. Patrick Goda
Los Alamos National Laboratory
Los Alamos, New Mexico USA
Tsunamis may be the most devastating source of economic damage
caused by asteroid impacts. The worldwide darkness, which may
last several months, caused by large asteroid impacts, such as
occurred after the KT impact, may kill more people by mass starvation,
especially in developing countries, than tsunami, but the dust
should not severely affect the economic infrastructure. The tsunami
may even kill more people in developed countries with a large
coastal population, such as the United States, than would worldwide
darkness. At Los Alamos we are in the middle of a systematic
study of asteroid tsunami. The study is divided into three parts:
a determination of those regions of the world that are most susceptible
to asteroid tsunami by simulating the effect of an asteroid impact
into mid-ocean, the simulation of the formation of the initial
crater by use of an SPH code, and a Monte Carlo study of the
accumulative effect of many small impactors on some of the more
strategically valuable regions that we find to be particularly
vulnerable in the first part of this study. The first part of
the study is well underway. Progress has been made on the other
two. The critical factor in the third part of the study is to
accurately determine the dispersion in the waves produced by
the smaller impactors. Dispersion may greatly reduce the effectiveness
of the smaller impactors at large distances from the impact point.
We wish to understand this effect thoroughly before going to
the Monte Carlo study. We have modeled mid-Atlantic impacts with
craters 150 and 300 km in diameter. We are proceeding to Pacific
impacts. The code has been progressively improved to eliminate
problems at
the domain boundaries, so it now runs until the tsunami inundation
is finished. We find that the tsunami generated by such impacts
will travel to the Appalachian mountains in the Eastern USA.
We find that the larger of these two impacts would engulf the
entire Florida Peninsula. The smaller one would cover the Eastern
third of the Peninsula while a wave passing through the Gulf
of Cuba would cause the inundation of the west coast of Florida.
HIGH FIDELITY COMPUTATIONAL
SIMULATIONS OF ASTEROID AND COMET IMPACTS
David Crawford
Computational Physics Department 9232
Sandia National Laboratory
Albuquerque, New Mexico USA
Of the 140 impact craters known on the surface of Earth, the
most famous was created about 65 million years ago when a 10
km asteroid or comet came down in shallow water near the present
day town of Chicxulub, Mexico. With a kinetic energy equivalent
to 100 trillion tons of TNT, the impact event lofted enough debris
onto globe-straddling trajectories to flash heat much of the
surface of the Earth and then darken the skies for several years.
Numerous investigations have demonstrated that such an event,
which happens, on average, every 100 million years, caused extreme
stress on Earth's climate and most likely led to the extinction
of many species. Recent high fidelity computational simulations
demonstrate that more numerous asteroids or comets as small as
1-2 km in diameter, impacting, on average, every 300,000 years
may be globally catastrophic-producing large tsunamis and lofting
debris to high altitudes worldwide. Indeed, the odds of an individual
dying from a relatively frequent 1-2 km impacting object (about
1 in 10,000) are substantially greater than from the impact of
an infrequent dinosaur killer (1 in 1,000,000). What can we do
to reduce the hazard from impacting comets and asteroids? Recent
computational investigations by Asphaug et al, suggest that weakly
bound asteroids (little more than rubble piles) are easier to
break than deflect (E. Asphaug, S. J. Ostro, R. S. Hudson, D.
J. Scheeres and W. Benz (1998), Nature, Vol. 393, pp. 437-440.).
Is this an advantage or disadvantage? Clearly, the mechanical
and compositional properties of asteroids and comets need to
be better understood if viable deflection technologies are to
be developed. Because the detection time prior to impact may
be months (long period comet) to years (asteroid or short period
comet
several orbits prior to impact), it is possible that we may not
have much time to perform such studies if faced with an actual
threat.
Related web sites:
http://sherpa.sandia.gov/planet-impact/comet/
http://sherpa.sandia.gov/planet-impact/asteroid/
ASTEROID IMPACT
TSUNAMI: A PROBABILISTIC HAZARD ASSESSMENT
Steven N. Ward and Erik Asphaug
University of California
Santa Cruz, CA USA
We investigate the generation, propagation, and probabilistic
hazard of tsunamis spawned by oceanic asteroid impacts. The process
first links the depth and diameter of parabolic impact craters
to asteroid density, radius, and impact velocity by means of
elementary energy arguments and crater scaling rules. Then, linear
tsunami theory illustrates how these transient craters evolve
into vertical sea surface waveforms at distant positions and
times. By measuring maximum wave amplitude at many distances
from a variety of impactor sizes, we derive simplified attenuation
relations that account both for geometrical spreading and frequency
dispersion of tsunamis on uniform depth oceans. In general, the
tsunamiwavelengths contributing to the peak amplitude coincide
closely with the diameter of the transient impact crater. For
the moderate size
impactors of interest here (those smaller than a few hundred
meters diameter), crater widths are less than or comparable to
mid-ocean depths. As a consequence, dispersion increases the
1/(sqrt r) long-wave decay rate to nearly 1/r for tsunamis from
these sources. In the final step, linear shoaling theory applied
at the wavelength associated with peak tsunami amplitude corrects
for amplifications as the waves near land. By coupling this tsunami
amplitude/distance information with the statistics of asteroid
falls, the probabilistic
hazard of impact tsunamis are assessed in much the same way as
probabilistic seismic hazard by integrating contributions over
all admissible impactor sizes and impact locations. In particular,
tsunami hazard, expressed as the Poissonian probability of being
inundated by waves 2 to 50 meter height in a 1000 year interval,
is computed at both generic (generalized geography) and specific
(real geography) sites.
For a conservative estimate of the impact flux, a typical generic
site with 180 degrees of ocean exposure and a 6,000 km reach
admits a 1:23 chance of an impact tsunami of 2 meter height or
greater in 1000 years. The likehood drops to 1:58 for a 5 meter
wave, and to 1:476 for a 25 meter wave. Specific sites of Tokyo
and New York have 1:38 and 1:76 chances of suffering an impact
tsunami greater than 5 meters in the next millennium. We believe
that investigations of this style that merge proper tsunami theory
with rigorous
probabilistic hazard analysis advance considerably the science
of impact tsunami forecasting.
ANIMATIONS
OF ASTEROID TSUNAMI INUNDATIONS
Charles L. Mader
Mader Consulting Co.
Honolulu, Hawaii, U.S.A.
The Asteroid Tsunami Program has as one of its objectives the
evaluation of the inundation of major coastal cities of the world
to be expected from mega-tsunamis generated by asteroids. The
regions studied include Japan, the U.S. East Coast, Los Angeles,
San Francisco, the Oregon coast, the Hawaiian Islands, Iceland
and the European coast. Some of the inundation studies have been
published. Computer animations generated as part of the studies
are also available. Many of the animations are included in the
directory TSUNAMI.MVE on the Science of Tsunami Hazards CD-ROM
included with the Tsunami Symposium Abstracts. The following
publications describe some of the inundation modeling shown in
the animations.
"Asteroid Tsunami Inundation of Hawaii,'' Science of Tsunami
Hazards, 14, 85-88 (1996)
"Asteroid Tsunami Inundation of Japan,'' Science of Tsunami
Hazards, 16, 11-16 (1998)
The tsunami inundation of the U.S. East Coast is described in
part in
"Tsunami Produced by the Impacts of Small Asteroids ,''
Jack G. Hills and Charles L. Mader, New York Academy of Sciences
822, 381-394 (1997).
MODELING THE
1958 LITUYA BAY MEGA-TSUNAMI
Charles L. Mader
Los Alamos National Laboratory
Los Alamos, New Mexico 87545 USA
Lituya Bay, Alaska is a T-Shaped bay, 7 miles long and up to
2 miles wide. The two arms at the head of the bay, Gilbert and
Crillon Inlets, are part of a trench along the Fairweather Fault.
On July 8, 1958, a 7.5 Magnitude earthquake occurred along the
Fairweather fault with an epicenter near Lituya Bay. A mega-tsunami
wave was generated that washed out trees to a maximum altitude
of 520 meters at the entrance of Gilbert Inlet. Much of the rest
of the shoreline of the Bay was denuded by the tsunami from 30
to 200 meters altitude. The SWAN code which solves the nonlinear
long wave equations was used to numerically model possible tsunami
wave generation mechanisms. A rockslide of about 30 million cubic
meters was probably triggered by the earthquake. It has been
assumed to have been the source of the tsunami wave even though
it was difficult to correlate with the eye-witness observations.
Numerical studies indicated that the tsunami wave generated by
the rockslide gave tsunami wave inundations that were less than
a tenth of those observed if the slide was assumed to lift a
volume of water corresponding to the volume of the slide to above
normal sea level. Another possible source of the tsunami was
a massive uplift of the sea floor along the Fairweather Fault
that underlies the Gilbert and Crillon Inlets at the head of
the bay. Even if all the water in the inlets was initially raised
to above normal sea level, the observedtsunami inundations could
not be numerically reproduced. Since it appeared that a much
larger source of water than was available in the inlet was required,
the one possible source was a partially subglacial lake near
the sharp bend in Lituya glacier which flows down Gilbert inlet.
The level of the lake was observed to have lowered 100 feet after
the earthquake. After the earthquake the glacial front of Lituya
Glacier had become a nearly straight wall and about 400 meters
of ice had been sheared off of the glacier front. Various models
of water flowing from breaking glacial dams were studied but
they did not reproduce the observations. Dr. George Pararas-Carayannis
suggested that a tsunami wave was formed by a rockslide impact
similar to an asteroid impact making a cavity to the inlet ocean
floor and a wave that splashed up to 520 meters height. If the
run-up was 50 to 100 meters thick, adequate water is available
between the slide and the run-up and the results are consistent
with the observations. Further studies will require full Navier-Stokes
modeling similar to those required for asteroid generated tsunami
waves.
ANALYSIS OF
MECHANISMS OF TSUNAMI GENERATON IN LITUYA BAY ON JULY 9, 1958
George Pararas-Carayannis
Honolulu, Hawaii USA
The giant waves that rose to a maximum height of 1720 feet at
the head of Lituya Bay on July 9, 1958 were generated by a combination
of disturbances triggered by a large, 8.3 magnitude earthquake
along the Fairweather fault. Several mechanisms for the generation
of the giant waves have been proposed, none of which can be conclusively
supported by the data on hand. Factors that contributed to the
giant waves in Lituya Bay were the result of cumulative effects
rather than those from a single source. Possible generative causes
include a combination of tectonic movements associated with the
earthquake, movements of a tidal glacier front, a major subaerial
rockslide/landslide in Gilbert Inlet, other subaerial or submarine
sliding at the head of the Bay, and the possible sudden drainage
of a subglacial lake on the Lituya Glacier. These factors are
examined, as well as the near field strong ground motions associated
with the earthquake. Dynamic earthquake ground motions lasting
40-60 seconds or more, rather than net crustal displacements,
may have contributed significantly to the generation of the giant
waves, particularly because of the orientation of the seismic
disturbance and the upper Lituya Bay's physical dimensions, geometrical
configuration and orientation with the Fairweather fault. Upper
Lituya Bay response and the associated secondary phenomena, contributing
to the giant slushing wave action in Gilbert Inlet, depended
on the earthquake's energy release, proximity to the epicenter,
physical rupture along the fault, propagation path of surface
seismic waves, and the magnitude and duration of the dynamic,
near-field, strong motions. Earthquake ground motions of high
intensity (XI, XII on the Modified Mercalli scale) could have
resulted in vertical accelerations of up to 0.75g and horizontal
accelerations of as much as 2.0g. In the absence of adequate
data for the Lituya Bay event, analogies are drawn from recorded
recent large earthquakes elsewhere, such as the 17 January 1994
Northridge earthquake in California, for their characteristics
of near field ground motions, duration, and the extent of vertical
and horizontal accelerations. Additionally, the tectonic setting
of the Fairweather fault is examined as characterized by past
events as the September 4, 1899, Cape Yakataga Earthquake.
The following mechanism can account for the giant 1720 foot wave
runup at the head and for the wave along its main body of Lituya
Bay: Almost immediately, the strong ground motions of the earthquake
triggered a giant landslide/rockslide at the headland of the
bay. Almost, instantaneously, this rockslide/landslide, acting
as a monolith and thus resembling an asteroid, impacted with
great force the bottom of Gilbert Inlet. The impact created a
crater which displaced and folded recent and Tertiary deposits
and sedimentary layers. The displaced water and the folding of
sediments broke and uplifted 1300 feet of ice along the entire
front of the Lituya Glacier. Also, the impact resulted in water
splashing action that reached the 1720 foot elevation on the
other side of inlet. The same landslide impact, in combination
with strong ground movements, the net vertical crustal uplift
of about 1 meter, and an overall tilting seaward of the entire
crustal block on which Lituya Bay was situated, generated a solitary
gravity wave which swept as an edge wave the main body of the
bay. An analytical solution based on this proposed impulsive
mechanism can further support the 1720-foot runup. Mathematical
modeling studies conducted by Dr. Charles Mader, support this
mechanism as there is a sufficient volume and an adequately deep
layer of water in the Lituya Bay inlet to account for the giant
wave runup. Dr. Mader has suggested full Navier-Stokes modeling,
as with asteroid generated tsunami waves. Necessary focus of
future research in understanding mega-tsunamis in enclosed bodies
of water, such as the Lituya Bay, should be directed towards
the examination and modeling of the elements relative to the
earthquake energy release, the empirical analysis of earthquake
source and seismic energy propagation processes, the near-field
ground motions from finite fault sources of past mega-thrust
earthquake events, and the systematic studies of resulting secondary
effects. Additionally, measurable input and output parameters
derived from mathematical modeling and analysis of the Lituya
Bay event can be further applied to models of asteroid tsunami
generation for purposes of calibration, verification and validation.
DID A "GIANT
WAVE'' STRIKE LANAI?
Barbara H. Keating and E. A. Felton
HIGP - University of Hawaii
Honolulu, Hawaii USA
Enigmatic geological features described from south Lanai, including
assemblages of marine faunas, apparently in situ, at elevations
of up to 329 meters, and the occurrence of gravel deposits containing
coral clasts dated at 101-115 Ka have been attributed to a ``Giant
Wave'' generated by a large submarine landslide off Hawaii approximately
105,000 years ago (Moore and Moore, 1984, 1988). It has also
been suggested that this wave traveled across the Pacific Ocean
and impacted the coast of southeastern Australia. the ``Lanai
tsunami'' runup is an order of magnitude greater than tsunami
runups in historic times. It is critical to assessments of tsunami
risk to verify that such a wave did indeed occur. Our review
of evidence cited in support of the giant wave hypothesis, including
ongoing field studies, leads us to question the validity
of the hypothesis. An examination of gravel stratigraphy at the
type section has identified and characterized a complex sequence
consisting of 15 beds, rather than 6 beds of alternating coral-rich
and coral-poor basalt illustrated by Moore and Moore (1988),
and interpreted by them to reflect the run-up and seaward return
flow of each of three waves in a tsunami wave train. Our studies
also show that deposition of the gravel sequence was punctuated
by at least three periods of subaerial exposure of sufficient
duration to allow soil formation, and several other erosional
breaks. This is inconsistent with a wholly tsunamigenic origion
for the deposit. Other observational evidence cited in support
of the giant wave hypothesis includes soil stripping from the
land surface up to 375 meters, deposition of a continuous blanket
of gravel (the Hulopoe Gravel) up the slopes of Lanai to 329
meters, and thinning and fining of this gravel landwards, could
not be verified in the field. A single giant wave event was suggested
by Moore and Moore (1984, 1988) based on radiometric dating of
a limited number of coral clasts from two locations, which yielded
a narrow range of dates. Larger numbers of recently reported
dates tend to cluster around 220 and 120 thousand years, periods
of former high sea level stands. While these dates record ages
of material in the deposits, they do not represent depositional
age(s). Without stratigraphic control of sampling, there can
be no assessment of whether dated material is eroded and re-deposited.
We suggest that the Hulopoe Gravel is a product of normal events
and processes occurring on a rocky, high-energy coast of a tropical
oceanic island.
THE 1998 PAPUA
NEW GUINEA TSUNAMI
Costas Synolakis
University of Southern California
Los Angeles, California USA
Shortly after 7 PM local time on July 17, 1998, more than 10
km ofthe northern PNG coastline home to at least 10,000 people
was swept clean by water approximately 10 m high. More than 2,200
people perished in the torrent or shortly thereafter. The scale
of the PNG tragedy coupled with unexpectedly large water wave
amplitudes for the earthquake size and the local geological complexity
motivated an intense international scientific effort to assess
if the tsunami was triggered by coseismic displacement or by
mass movements.
The July 17, 1998, tsunami that struck Sissano, Sandaun Province,
Papua New Guinea (PNG) is the first major tsunami linked directly
to a giant mass movement. This event is also a milestone in that
modeling efforts have been simultaneously informed by marine
surveys and geological analyses carried out on the Kairei (KR98-13)
and Natsushima (NT99-02) joint Japan Marine Science and Technology
Center (JAMSTEC) and South Pacific Applied Geoscience Commission
(SOPAC) cruises. We describe the first effort to model tsunami
generation, propagation, and coastal interaction based on recent
bathymetric data, geological interpretation, and tethered ROV
(Dolphin 3K) investigations of the seafloor.
ANATOMY OF
A LANDSLIDE-CREATED TSUNAMI AT SKAGWAY, ALASKA
Bruce A. Campbell, P.E.
Dennis Nottingham, P.E.
Peratrovich, Nottingham and Drage, Inc.
Anchorage, Alaska USA
At 7:10 p.m. on November 3, 1994, a large tsunami generated by
a massive landslide in the submerged Skagway River delta occurred
near Skagway, Alaska, resulting in one fatality and damaging
or destroying many harbor structures. At first, it was theorized
by some that construction activity in the harbor caused the initial
landslide. However, this paper presents the findings of an in-depth
scientific investigation that concludes that such a theory is
impossible. The findings paint a clear picture of the failure
of the submerged Skagway River delta that was overloaded by flood
sediments and exacerbated by river diking. Slide volumes estimated
at over 20 million cubic yards that consisted of a massive initial
slide and subsequent retrogressive earth slide produced the tsunami
that caused one fatality and destroyed or damaged harbor structures.
The analysis relies on physical evidence and reconstructs the
tsunami on a second-by-second time-line that shows conclusively
that the failure of the submerged Skagway River delta was not
caused by the harbor construction. Each shred of evidence is
examined and the event systematically reconstructed on a step-by-step
basis without interjecting supposition, speculation, theory or
hypotheses.
1983 to 2000
GLOBAL TSUNAMI CATALOG
James F. Lander, Lowell S. Whiteside, and Karen Fay O'Loughlin
National Geophysical Data Center
Boulder, Colorado USA
We are preparing a global historical tsunami catalog for the
period from 1983 through the end of 1999. This catalog will bring
the previous Pacific Catalog by Soloviev up to date to the end
of the millennium. It will, however, also include tsunamis from
all worldwide sources available to make it the first global tsunami
catalog. We have collected data on 136 tsunamis so far, including
119 from the Pacific, 9 in the Mediterranean, 5 in the Caribbean,
and one each from the South China Sea, the Seychelles Islands
in the Indian Ocean, and the Gulf of Aqaba near the Red Sea.
Efforts to promote accuracy and completeness include contacts
with local sources to see if smaller earthquakes caused unreported
small tsunamis and a call for the preservation of maregrams and
other data to fortify the record. The Millennial Tsunami Catalog
manuscript will be posted on a website for review before being
published by the NationalGeophysical Data Center early in the
year 2000. After publication, additional tsunami reports, updates,
and corrections will be added
to the online catalog. An up-to-date global historical catalog
of tsunamis could thus be published directly when wanted.
PACIFIC TSUNAMI
WARNING CENTER: RECENT DEVELOPMENTS
Charles S. McCreery
Pacific Tsunami Warning Center
Ewa Beach, Hawaii USA
Operational activities of the Pacific Tsunami Warning Center
can be classified into four major categories: collection and
processing of seismic data, collection and processing of water
level data, decision making, and dissemination of message products.
Over the past few years significant improvements have been made
or are underway in all these areas that are enabling PTWC to
be faster, more accurate, more reliable, and more effective.
The amount and quality of continuous seismic waveform data received
at PTWC has increased substantially with the acquisition from
the US Geological Survey of an Earthworm seismic data collection
and processing system, and establishment of high-speed dedicated
digital links between PTWC, the West Coast / Alaska Tsunami Warning
Center, the National Earthquake Information Center, and the Hawaii
Volcanoes Observatory. Water level data in near real time are
now being received from five stations along the Pacific coast
of Japan; two new stations are scheduled for installation this
summer in the Kuril-Kamchatka region; and ten new stations are
being installed along the coast of Chile. Development by the
Pacific Marine Environmental Laboratory of real-time-reporting
deep-ocean pressure gauges is continuing, with up to six gauges
in the north and northwest Pacific planned for deployment over
the next few years. Better and faster techniques for estimating
tsunamigenic potential and predicting impacts using seismic and
water level data have recently been developed and are being implemented
in the decision-making process for warnings and cancellations.
Message dissemination continues over longstanding dedicated circuits
such as GTS and AFTN, while new opportunities for sending both
text and graphical information over higher bandwidth and more
widely available links such as the Internet and the Emergency
Managers Weather Information Network are being developed.
THE U.S. WEST
COAST AND ALASKA TSUNAMI WARNING CENTER
Thomas J. Sokolowski
West Coast and Alaska Tsunami Warning Center
Palmer, Alaska
The Alaska Tsunami Warning Center (ATWC) was established in Palmer,
Alaska in 1967 as a direct result of the great Alaskan earthquake
that occurred in Prince William Sound on March 27, 1964. In 1996,
the responsibility was expanded to include all Pacific-wise tsunamigenic
sources which could affect California, Oregon, Washington, British
Columbia and Alaska coasts and the center became the West Coast/Alaska
Tsunami Warning Center (WC/ATWC). An on-going project at WC/ATWC
is the prediction of tsunami amplitudes outside the tsunami generating
area described in Science of Tsunami Hazards 14, 147-166 (1996).
The basic idea behind this technique is that pre-computed tsunami
models can be scaled by
recorded tsunami amplitudes during an earthquake to give a reasonable
amplitude estimate outside the source zone. Tsunami models for
moment magnitude 7.5, 8.2, 9.0 earthquakes have been computed
along the Pacific plate boundary from Honshu, Japan to the Cascadia
subduction zone. The modeling technique was verified by comparison
to historic tsunamis from different regions. At present, the
results from the scaled models are not distributed to the emergency
officials during warnings, but are used only internally
as an aid in canceling or extending warnings. Another current
project at WC/ATWC is to receive tsunami data from the Pacific-wide
tsunami sites via a satellite phone system. Due to the current
delay of 1 to 3 hours in receiving tide data from NOS gauges,
selected windows of data can be received from these tide sites
using a satellite phone, antenna, PC computer and special hardware
inserted into the current NOS field packages. This will permit
obtaining data from selected tide sites nearest the tsunami source.
WC/ATWC conducts a community preparedness program which provides
advice and training sesssions to coastal citizens and emergency
managers to aid in pre-event planning. The aim of the program
is to educate the public to help themselves if they are caught
in the middle of a violent earthquake and/or tsunami, and to
be aware of the safety procedures, safe areas, and the limitation
of the Tsunami Warning System.
JAPANESE TSUNAMI
WARNING SYSTEM
Augustine S. Furumoto
Honolulu, Hawaii USA
Hidee Tatehata
Japan Meterological Agency, Tokyo, Japan
Chiho Morioka
Construction Technology Institute, Tokyo, Japan
As Japan is a nation small in area and surrounded by seas, a
potential threat of a destructive tsunami becomes a national
event. The Japan Meterological Agency, an agency of the national
government, has the mandate to issue tsunami warnings. By using
an archive of precalculated tsunami scenarios, the agency can
forecast wave heights for all the coasts of Japan, when the magnitude
and epicenter of the generating earthquake are known. Tsunami
warnings and forecasts start from the cabinet level of the national
government and are transmitted through the various layers of
the national government, to the prefecture governments and eventually,
in a matter of minutes, to the local governments. Transmissions
of the warning and forecasts from the local governments to the
general public is done through a variety of media. The
response of the warning system to the Sea of Japan tsunami of
July 12, 1993, was well documented and showed successes and loopholes.
CARIBBEAN
TSUNAMIS AND WARNING SYSTEM STATUS
James F. Lander, Lowell S. Whiteside, and Karen Fay O'Loughlin
National Geophysical Data Center
Boulder, Colorado USA
Greater numbers of civil defense and other pertinent personnel
are becoming aware of the nature of the tsunami hazard in the
Caribbean. Interest is growing for establishing a warning system
and creating plans for mitigation of damages, search and rescue
operations, and education of the public and key officials, coordinated
among the numerous political divisions in the area, and perhaps
land use planning, engineering, and insurance programs. A history
of prior occurrences and effects is key to understanding the
local nature of the hazard and for designing the most effective
plan for warning and mitigation systems. We have submitted a
paper,`Caribbean Tsunamis: A 500 Year History, 1498 to 1998,''
with data on 88 Caribbean Tsunamis for publication. The hope
is to establish a warning system and general education on the
nature of the hazard before the next disaster. Plans to establish
a region-wide Tsunami Warning System received a boost with the
involvement of the IOC-IOCARIBE in planning, coordination, and
other assistance, beginning in 1996, at the May Caribbean Tsunami
Workshop, held on St. John, U.S. Virgin Islands. Because most
tsunamis are quite small, relatively rare, and do little damage,
they have often been overlooked as a natural hazard until a disastrous
event occurs. The region has averaged about one damaging tsunami
every 26 years, but since they have not had one in 53 years,
a destructive tsunamis is overdue. With the increase in population,
tourism, coastal development, and also rising sea levels, the
hazard is greater. The 500-year history shows that tsunamis in
the Caribbean have the potential to produce major regional or
local disasters. These can be mitigated through proper preparation.
The state of tsunami preparedness in the Caribbean today is similar
to that in the Pacific prior to the establishment of the PacificTsunami
Warning System. Without a warning system little or nothing could
be done to mitigate disaster. As many as 9600 fatalities have
been reported as due to tsunamis and tsunamigenic earthquakes
in the Caribbean. The upcoming area-wide workshop organized by
the IOC-IOCARIBE, ``Intra-American Sea Tsunami Warning System,''
on April 24-26, 1999, at San Jose, Costa Rica, will set the course
of the Caribbean Warning System, helping to determine the tsunami
hazard mitigation needs.
CONTEMPORARY
ASSESSMENT OF TSUNAMI RISK AND IMPLICATIONS FOR EARLY WARNINGS
FOR AUSTRALIA AND ITS ISLAND TERRITORIES
Jack Rynn
Center for Earthquake Research, Indooroopilly, Australia
Jim Davidson
Bureau of Meteorology, Brisbane, Australia
The natural hazard of tsunamis relative to Australia and its
Island Territories has been perceived to be of little or no consequence
-- and hence a small risk -- when compared to other more frequent
natural disasters of meteorological origin, or even occasional
earthquakes. The historical record shows that tsunami damage,
although rare, has occurred along the eastern seaboard (from
the 1877 and 1960 Chile earthquakes), and northwest coast (from
the 1883 Krakatoa (Indonesia) volcanic eruption and the 1977
and 1994 (Indonesia) earthquakes) of the continent. Because of
the infrequent occurrences of tsunamis, they are little known
and, in some cases, have been forgotten. However there is a need
for tsunami mitigation, because, as an island nation, Australia
is totally dependent on its coastal facilities for sustainable
development, with more than 90% of the population domiciled in
this environment. Recent devastating tsunamis in the Pacific
region emphasise this need. As part of Australia's contribution
to the United Nations IDNDR (1990-2000) program, Emergency Management
Australia's IDNDR Coordination Committee specifically directed
one project to access the risk of tsunamis on the shorelines
of Australia and its island territories. A specific methodology
was developed, invoking a multidisciplinary approach to quantitatively
and qualitatively define the hazard and the vulnerability, and
then integrate these elements into a comprehensive risk assessment.
More than 350 earthquakes and specific submarine volcanoes and
landslides were considered as possible tsunamigenic sources.
In the period 1788 through 1995 more than 60 registrations on
tide-gauge records were identified, together with anecdotal information.
The outcomes have been presented as an ``information resource''
in terms of hazard, vulnerability and risk assessment maps and
commentaries, comprehensive tsunami data base, maps of potential
tsunamigenic sources, tsunami travel time charts and relationships
between
relevant tsunami parameters. These outcomes have been delineated
in terms of proactive applications necessary to upgrade both
tsunami warning procedures by the Bureau of Meteorology and response
actions through counter disaster planning by the emergency service
authorities. As such, Australia is currently developing its own
regional tsunami warning system.
LANDSLIDE
TSUNAMIS: GENERATION, DETECTION AND WARNING
Sin-Iti Iwasaki and Shoji Sakata
National Research Institute
Tsukuba, Japan
The most remarkable difference of tsunami characteristics due
to a landslide and an earthquake is the movement of the source
region. For a landslide, the source region moves horizontally.
For an earthquake the source region (usually 100 kilometer or
more wide) only moves vertically, this volume change converted
to sea surface. So the long wave approximation is valid for tsunamis
generated by earthquakes, but not for landslides. A new simulaton
method was developed for submarine landslide tsunamis based on
the combination of analytical and numerical calculations. The
landslide results showed strong directivity compared with tsunamis
generated by earthquakes. For the detection and early warning
for these tsunamis, it is necessary to observe not only tsunami
wave heights but also its directivity. For this purpose, the
present status of tide gauge distribution even in the Pacific
region is not adequate. I propose a cable system using laser-tsunami
meters. The total cost of the cable system including installation
will be inexpensive compared with the cable systems currently
deployed around Japan.
DESTRUCTIVE
TSUNAMIS AND TSUNAMI WARNING IN CENTRAL AMERICA
Mario Fernandez
CIGEFI, RSN:ICE-UCR San Jose, Costa Rica
Jens Havskov and Kuvert Atakan
University of Bergen, Bergen, Norway
The Central American Coasts have been hit by nine destructive
tsunamis during the last two centuries. Seven of these tsunamis
are from the Pacific and two from the Caribbean. Reported damages
range from coastal and ship damage to destruction of small towns.
Almost 500 people have been killed by these tsunamis. The Pacific
coast of Central America has higher tsunami hazard than the Caribbean
Coast. Tectonic environments that generate tsunamigenic earthquakes
are the Middle American Trench, the Polochic-Motagua Fault System
and the North Panama Deformed Belt (NPDB). A Tsunami Warning
System for Central America has been designed. This system uses
earthquake magnitude as the trigger for tsunami warning. Three
institutions are involved in this system: The Instituto de Estudios
Territoriales de Nicaragua (INETER), the Central American Seismological
Center (CASC) and the National Emergency Office (NEO) of each
country. CASC locates the
earthquake and determines the magnitude and sends the seismic
information to INETER. This institution evaluates the seismic
information and decides if the earthquake has potential to generate
a tsunami. In the event of a tsunamigenic earthquake INETER issues
a tsunami warning which is sent to the National Emergency Office
(NEO). NEO activates the local emergency plan and takes actions
to protect coastal residents.
ISSUES RELATED
TO LOCAL TSUNAMIS IN HAWAII
Daniel A. Walker
HIG - University of Hawaii
Honolulu, Hawaii USA
A review of historical data for locally generated tsunamis suggests
average recurrence intervals of about 20 years for destructive
tsunamis, with the last such tsunami occurring in 1975. Preliminary
modeling indicates that a large tsunami generated on the Kona
Coast could have significant destructive potential on other islands,
especially on the south shore of Oahu. Unfortunately, the recurrence
interval for such large tsunamis on the Kona Coast is not known.
In evaluating local warning system capabilities and limitations,
it should be noted that warnings based only on earthquake magnitudes
will have an unacceptably high failure rate.
Incorporating conventional tide gauge readings into the decision
making process with magnitude determinations may moderately reduce
this failure rate. An acceptable warning system will require
(1) many more wave recorders than the three now present on the
Big Island; (2) modeling studies of wave heights or runups at
instrumented sites for a suite of possible tsunamigenic earthquakes
along the Puna, Kau, and Kona coasts; (3) perhaps a new generation
of tsunami detectors; and (4) automated warnings for highly localized
tsunamis.
TSUNAMI WARNING
SYSTEMS IN THE U.S.A
Augustine S. Furumoto
Honolulu, Hawaii, U.S.A.
In the U.S.A. tsunami warnings are issued by the West Coast/Alaska
Tsunami Warning Center and the Pacific Tsunami Warning Center,
but the practical task of informing the general populace and
evacuating people from potential tsunami inundation areas are
the responsibility of state authorities. Of the various Pacific
states, Hawaii has the most developed and proven tsunami warning
and evacuation system. The warning systems of other states --
Alaska, California, Oregon and Washington -- are at various stages
of approaching the Hawaii model. A federal agency, the Pacific
Marine Environmental laboratory, a division of NOAA, has established
the National Tsunami Mitigation Program to assist the states.
FINITE ELEMENT
MODELING OF POTENTIAL CASCADIA SUBDUCTION ZONE TSUNAMIS
Edward P. Myers and Antonio M. Baptista
Oregon Graduate Institute of Science and Technology Portland,
Oregon USA
George R. Priest
Oregon Department of Geology and Mineral Industries Portland,
Oregon USA
Evidence of historic Cascadia subduction zone earthquakes and
subsequent tsunamis have prompted hydrodynamic modeling efforts
to identify potential flow patterns and coastal hazards for plausible
future events. In this study we identify the methods used to
derive potential seismic source scenarios and present a thorough
evaluation of finite element simulations of the tsunamis associated
with these scenarios. The first part of the paper deals with
regional impacts of potential tsunamis, while the second part
evaluates the fate
of the modeled waves from the local perspectives of Seaside and
Newport, Oregon. Both parts are composed of physical as well
as numerical interpretations of the simulations. Regional analyses
of the simulations help identify the factors influencing the
propagation of the waves from the source to the coastline. The
local analyses will then evaluate the fate of the tsunami waves
as they interact with the coast line and the topography of the
land. Enough grid refinement is added to capture the dynamic
intensity of the waves at local spatial scales. The physical
interpretation of both these results provides clues to the determining
factors in the fate of tsunami waves. The numerical interpretation,
likewise, is a crucial component in helping to assess the usefulness
of numerical models in evaluating and mitigating tsunami hazards.
The identification of the limits of a numerical model and how
those limits can be minimized in turn allows the physical mechanisms
to be better represented and the mitigation to be more effective.
It is the mitigation, after all, which is the goal of a study
such as this. For example, the state of Oregon is utilizing these
results to estimate potential inundation patterns resulting from
Cascadia tsunamis. These patterns have been translated into inundation
maps identifying zones of low, medium, and high risk of flooding
throughout coastal communities. The results presented for Seaside
and Newport, Oregon identify the physical characteristics of
the waves responsible for inundation in those communities. Such
results are being used by the Oregon Department of Geology and
Mineral Industries and NOAA to mitigate local tsunami hazards
with inundation maps and community awareness. A comprehensive
version of this work is available on the Science of Tsunami Hazards
Web site at
http://www.ccalmr.ogi.edu/STH/online/volume 17/ number 1/mbp/.
CASCADIA PALEOTSUNAMIS:
RECONSTRUCTING RECURRENCE AND RUNUP FROM LAKE
DEPOSITS ON VANCOUVER ISLAND
Ian Hutchinson, John Clague, Rolf Mathewes
Simon Fraser University, Burnaby, Canada
Peter Bobrowsky
BC Geological Survey, Victoria, Canada
Tsunami run-up and recurrence may be reconstructed from sediment
sequences in near-coastal lakes. We present a partial chronology
for tsunamis generated at the Cascadia subduction zone from an
analysis of sediments in Kanim, Catala, Deserted, and Kakawis
lakes on the west coast of Vancouver Island, British Columbia.
Basal marine sand, gravel and shell in these lakes are overlain
successively by fine-grained lagoonal sediments and freshwater
gyttja. The change from a marine environment through an intertidal
environment to a freshwater one is the result of regional uplift
at a rate of about 1 meter per thousand years.
Inferred tsunami deposits in the lagoonal sediments and gyttja
consist of massive to graded sand or gravel overlain by, or interbedded
with, thin layers of forest detritus. The tsunami deposits commonly
contain marine microfossil assemblages which are strikingly different
from the microfossil assemblages in the enclosing gyttja. As
a result of regional uplift, the lakes progressively emerge above
the zone of tsunami influence. A complete tsunami history for
northern Cascadia, therefore, requires systematic sampling of
lakes
across a range of elevations. Currently we have evidence of major
tsunami events dating from about 300, 1000-1400, 1600-1700 and
2700-2800 years ago. The overlap between these dates and the
ages of inferred earthquakes at the Cascadia subduction zone
suggests that all of these tsunamis were locally generated. Calculations
of runup for these events are complicated by local variations
in shoreline configuration, and the fact that the distance between
the lake and the sea commonly increases as the lake emerges,
but initial estimates suggest that runup magnitudes on the outer
coast average less than 5 meters.
TSUNAMI MITIGATION
FOR THE CITY OF SUVA, FIJI
Jack Rynn
Center for Earthquake Research, Indooroopilly, Australia
Gajendra Prasad, Ato Kaloumaira
Republic of Fiji, Suva, Fiji
At about 12:30 p.m. (local time) on September 14, 1953, the city
of Suva was devastated by an ML 6.5 earthquake and associated
tsunami of local origin. The earthquake source was about 25 km
SW of Suva and the tsunami generation was attributed to submarine
landslides (turbidity currents). The main industrial area and
shore and harbour facilites of Suva were severly damaged. As
part of the UNDHA - South Pacific Programme Office ``South Pacific
Disaster Reduction Programme'', within the auspices of the Pacific
Region IDNDR and the 1994 Yokohoma Statement, the ``Suva Earthquake
Risk Management Scenario Pilot Project'' (SERMP) was faciliated
for the Government of the Republic of Fiji. SERMP considered
mitigation measures for both earthquake and tsunami impacting
upon the city of Suva, with the scenario event based on the real
experience of the 1953 Suva earthquake and tsunami. A specific
tsunami mitigation methodology was developed involving a multidisciplinary
approach with multi-agency cooperation to address in both quantitative
and qualitative terms, the premise RISK = HAZARD X VULNERABILITY
and then integrate the assessments in terms of Fiji's emergency
management requirements. The outcomes include hazard, vulnerability
and risk zonation maps with associated commentaries, estimates
of relevant tsunami
parameters and possible damage situations. It was concluded that
a significant risk of a local tsunami does exist for the city
of Suva and its harbour environs. Practical applications of these
results, in terms of community vulnerability and reduction of
potential losses, and including a simulated tsunami exercise,
have been a major element in this project. This information resource
has been implemented for Fiji's National Disaster Management
Office in terms of disaster planning, response actions, training
and community
education. Currently, Fiji is developing its own regional tsunami
warning system. Recent tsunami disasters, like that in Papua
New Guinea in July 1998, serve to reinforce the vital need for
mitigation measures in these vulnerable coastal communities of
Pacific Island nations.
THE PACIFIC
TSUNAMI MUSEUM: A Memorial to Those Lost to Tsunamis and An Education
Center to
Prevent Future Casualities
Walter C. Dudley
University of Hawaii, Hilo, Hawaii USA
In spite of significant advances in our understanding of the
science of tsunamis, the basic facts about the dangers of tsunami
waves are not understood by the general public. Tsunamis are
the most deadly natural disaster facing those living in the Hawaiian
Islands, having resulted in some 291 fatalities since 1837. The
town of Hilo in particular has suffered great destruction and
loss of life with 177 victims, therefore making it an appropriate
site for a museum focused on tsunamis. In mid-1998 the Pacific
Tsunami Museum opened in downtown Hilo. The museum has two goals:
(1) to preserve the local history of tsunamis in Hawaii as a
memorial to those lost, and (2) to prevent future loss of life
from tsunami waves by fostering tsunami
education, preparedness, and other mitigating measures. These
two goals are compatible and produce a powerful synergism. The
local history of tsunamis in Hawaii contains many true stories
of tragedy, sacrifice and heroism, as well as accurate descriptions
of the tsunami run-up phase. It is the power of these true stories
as told by the survivors themselves which has the ability to
capture the imagination and educate audiences of residents and
visitors who most need to understand the danger of tsunamis.
Funded by private donations and a grant from FEMA, the museum
is currently planning a dozen permanent exhibits to be installed
by the end of 1999. An ambitious outreach program is already
underway and includes development of curriculum packages for
all public and private schools statewide, plus specialized literature
targeted at specific groups including surfers, boaters, visitors,
businesses occupying inundation areas, etc.The museum has established
an archive collection of photographs, films, videos, and artifacts,
which will be made available to other educational organizations
around the world, and has already assisted in the production
of television documentaries aired nationally including those
produced by the National Geographic Society, the Discovery Channel,
and the History Channel. A tsunami education special was produced
by KGMB-TV and shown in Hawaii during Tsunami Awareness Month.
Future plans for exhibits, educational programs, and possible
alliances with the tsunami research community will be discussed.
TSUNAMIS ON
THE COAST LINES OF INDIA
T. S. Murty
Baird and Associates Coastal Engineers
Ottawa, Canada
A. Bapat
Sadashiv Peth, Puna, India
Although the majority of the reported tsunamis are from littoral
countries of the Pacific Ocean, there are a few cases of tsunamis
in the Indian Ocean. The approximate length of the Indian coast
is about 6000 kilometers. The coasts run from north to south
and have two arms in the east and west with a tapering end at
Kanyakumari. The tsunamigenic earthquakes occur mostly at the
following three locations; (1) The Andaman sea, (2) Area about
400-500 kilometers SSW of Sri Lanka (Ceylon), (3) The Arabian
Sea about 70-100
kilometers south of Pakistan Coast -- off Karachi and Baluchistan.
The oldest record of tsunami is available from November 326 BC
earthquake near the Indus delta/Kutch region. Alexander the Great
was returning to Greece after his conquest and wanted to go back
by a sea route. But an earthquake of large magnitude destroyed
the mighty Macedonian fleet as reported by Lietzin (1974). The
earliest record of tsunami is reported to be about 1.5 meters
at Chennai (formerly Madras) which was created due to the August
8, 1883 Krakatoa volcanic explosion in Indonesia. An earthquake
of magnitude 8.25 occurred about 70 kilometers south of Karachi
(Pakistan) at 24.5 N and 63.0 E on November 27, 1945. This created
a large tsunami of about 11.0 to 11.5 meters high on the coasts
of India in the Kutchch region, as reported by Pendse (1945).
An earthquake of magnitude 8.1 occurred in the Andaman Sea at
12.9 N and 92.5 E on June 26, 1941 and a tsunami hit the east
coast of India. As per non-scientific/journalistic sources, the
height of the
tsunami was of the order of 0.75 to 1.25 meters. At the time
no tide gauge was in operation. Mathematical calculations suggest
that the height could be of the order of 1.0 meter. There are
a few more cases of earthquakes of magnitude less than 8.0 which
have given rise to some smaller tsunamis. Bapat, et al (1983)
have reported a few more earthquakes on the coast of Myanmar
(formerly Burma).
PALEOTSUNAMIS
ALONG THE AUSTRALIAN COAST
Jonathan Nott
James Cook University, Cairns, Australia
Edward Bryant
University of Wollongong, Wollongong, Australia
The Australian continent has not been impacted by large or devastating
tsunamis since European colonization over 200 years ago. As a
consequence this country is normally viewed as largely protected
from impact of, or too far removed from the source of these hazards.
Considerable evidence exists, however, to show that very large
waves have struck the coast of Australia in the relatively recent
past. This evidence occurs along the eastern, northern and western
Australian shores and also occurs within seemingly protected
areas such
as along the mainland coast inside the Great Barrier Reef in
northeast Queensland and within the Gulf of Carpentaria which
is an epicontinental sea with a maximum depth of 60 meters. The
evidence is in the form of shell and coral deposits on top of
headlands many tens of meters in height, sand deposits containing
large boulders, shell and coral 20 - 30 meters above modern sea
level and several kilometers inland, fields of large imbricated
boulders across shore platforms and sculptured bedrock forms.
The size of the transported boulders together with numerical
modeling, and the heights above sea level of these deposits suggests
that tsunamis are responsible as opposed to large storm waves.
The orientation of boulders and bedform deposits provide paleowave
directions for much of the continent's coast allowing reasonable
estimation of the source and possible generating mechanism of
the tsunami. Carbon dating of these deposits show that at least
two very large tsunami events have occurred along this coast
during the last millennium.
GEOLOGICAL
AND HISTORICAL RECORDS OF TSUNAMIS: THE IMPORTANCE OF DATA
INTEGRATION WITH REFERENCE TO SOME TSUNAMIS IN GREECE
Dale Dominey-Howes
Coventry University
Conventry, United Kingdom
This paper provides information concerning an effective methodology
of investigating past tsunami events developed following the
geological investigation of recent, historical and paleohistoric
tsunamis in the Aegean Sea region of Greece. The methodology
described includes the use of contemporary and historical records,
recent scientific publications, eye-witness accounts, geomorphological
mapping and analyses and laboratory analysis of tsunami-deposited
sediments. From the data presented, it will be seen that a multidisciplinary
approach to the investigation of individual tsunami events is
preferable because either insufficient or misleading evidence
may be obtained when only one method is used. The paper describes
how geomorphology may be used to infer the magnitude and likely
effects of coastal tsunami flooding.
Additionally, the paper considers the accuracy of historical
records of individual tsunami flood events and how inaccurate
recording can have important implications for disaster preplanning
and coastal vulnerability reduction. The Aegean tsunamis of September
29, 1650 and July 9, 1956 are used to illustrate the methodology
described. Data are also presented which indicate that it is
possible to distinguish episodes of coastal tsunami flooding
within the long-term geological record on the basis of the microfossil
(Foraminifera)
assemblage. Such analysis may assist in the reconstruction of
the number of paleotsunami events with specific coastal areas
providing a valuable predictive tool for future tsunami recurrence.
METHODS OF
CALCULATION OF TSUNAMI RISK
George D. Curtis
University of Hawaii, Hilo, Hawaii USA
Efim N. Pelinovsky
Institute of Applied Physics, Nizhny, Novgorod, Russia
A hazard is a potentially perilous event, such as a tsunami,
while risk is the probability that the hazard will occur repeatedly
and affect a specified population. Risk includes the frequency
of occurrence, exposure, and magnitude. The International Decade
for Disaster Reduction has focussed attention on assessing and
mitigating the risk of tsunamis. Statistical and scenario methods
of determining risk for rare and more common events are discussed.
The problems of warning are considered, and a matrix illustrating
the most
effective use of research, mitigation, and warning programs is
presented. Emphasis is on public safety, with due consideration
of public property factors. Examples of evaluation of relative
risk are provided.