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INTERNATIONAL
TSUNAMI SOCIETY
P. O. Box 2117,
Ewa Beach,
HAWAI'I 96706-0117
U.S.A.
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SCIENCE
OF TSUNAMI HAZARDS
The
International Journal of the Tsunami Society
Volume
27, No. 2 - Year
2008
ISSN 8755-6839
ABSTRACTS
NOAA/WEST
COAST AND ALASKA TSUNAMI WARNING CENTER PACIFIC OCEAN RESPONSE
CRITERIA
Paul Whitmore
- NOAA/West Coast/Alaska
Tsunami Warning Center - Palmer, Alaska
Harley Benz - USGS/National
Earthquake Information Center - Golden, Colorado
Maiclaire Bolton - British
Columbia Provincial Emergency Program - Victoria, British Columbia
George Crawford - Washington
Emergency Management Division - Camp Murray, Washington
Lori Dengler - Humboldt
State University - Arcata, California
Gerard Fryer - NOAA/Pacific
Tsunami Warning Center - Ewa Beach, Hawaii
Jim Goltz - California
Office of Emergency Services - Pasadena, California
Roger Hansen - University
of Alaska, Fairbanks - Fairbanks, Alaska
Kelli Kryzanowski - British
Columbia Provincial Emergency Program - Victoria, British Columbia
Steve Malone - University
of Washington - Seattle, Washington
David Oppenheimer - USGS/Earthquake
Hazards Team - Menlo Park, California
Ervin Petty - Alaska
Division of Homeland Security and Emergency Management - Anchorage,
Alaska
Garry Rogers - Geological
Survey of Canada, Pacific Geoscience Centre, Sidney, British
Columbia
Jay Wilson - Oregon
Emergency Management -Salem, Oregon
ABSTRACT
New West Coast/Alaska
Tsunami Warning Center (WCATWC) response criteria for earthquakes
occurring in the Pacific basin are presented. Initial warning
decisions are based on earthquake location, magnitude, depth,
and - dependent on magnitude - either distance from source or
pre-computed threat estimates generated from tsunami models.
The new criteria will help limit the geographical extent of warnings
and advisories to threatened regions, and complement the new
operational tsunami product suite.
Changes to the previous criteria include: adding hypocentral
depth dependence, reducing geographical warning extent for the
lower magnitude ranges, setting special criteria for areas not
well-connected to the open ocean, basing warning extent on pre-computed
threat levels versus tsunami travel time for very large events,
including the new advisory product, using the advisory product
for far-offshore events in the lower magnitude ranges, and specifying
distances from the coast for on-shore events which may be tsunamigenic.
This report sets a baseline for response criteria used by the
WCATWC considering its processing and observational data capabilities
as well as its organizational requirements. Criteria are set
for tsunamis generated by earthquakes, which are by far the main
cause of tsunami generation (either directly through sea floor
displacement or indirectly by triggering of slumps). As further
research and development provides better tsunami source definition,
observational data streams, and improved analysis tools, the
criteria will continue to adjust. Future lines of research and
development capable of providing operational tsunami warning
centers with better tools are discussed.
Science of Tsunami
Hazards, Vol. 27, No. 2, page 1 (2008)
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DID
A SUBMARINE SLIDE TRIGGER THE 1918 PUERTO RICO TSUNAMI?
Matthew J. Hornbach - Institute
for Geophysics, Jackson School of Geosciences, Univ. of Texas
at Austin, Texas, USA.
Steven A.
Mondziel - Univ.
of North Carolina, Dept. of Geography and Geology. Wilmington,
North Carolina, USA.
Nancy R. Grindlay
- Univ. of North
Carolina, Dept. of Geography and Geology. Wilmington, North Carolina,
USA.
Cliff Frohlich
- Institute for Geophysics,
Jackson School of Geosciences, Univ. of Texas at Austin, Texas,
USA.
Paul Mann
- Institute for Geophysics,
Jackson School of Geosciences, Univ. of Texas at Austin, Texas,
USA.
Corresponding author: Matthew J. Hornbach matth@ig.utexas.edu
ABSTRACT
The 1918 tsunami that
inundated northwest Puerto Rico with up to 6 m waves has been
attributed to seafloor faulting associated with the 1918 Mona
Canyon earthquake. During the earthquake a series of submarine
cable breaks occurred directly off the northwest coast of Puerto
Rico where the largest tsunami waves came ashore. Here, we use
a recently compiled geophysical data set to reveal that a 9 km
long landslide headwall exists in the region where cable breaks
occurred during the 1918 earthquake. We incorporate our interpretations
into a near-field tsunami wave model to evaluate whether the
slide may have triggered the observed 1918 tsunami. Our analysis
indicates that this slide could generate a tsunami with phase,
arrival times, and run-ups similar to observations along the
northwest coast of Puerto Rico. We therefore suggest that a submarine
slide offers a plausible alternative explanation for generation
of this large tsunami.
Science of Tsunami
Hazards, Vol. 27, No. 2, page 22 (2008)
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TSUNAMIGENIC
SOURCES IN THE INDIAN OCEAN
R. K. Jaiswal
- Institute of Seismological
Research, Gandhinagar-382 018, Gujarat (India)
B. K. Rastogi
- Institute of Seismological
Research, Gandhinagar-382 018, Gujarat (India)
Tad S. Murty
- University of Ottawa,
Ottawa, Canada
Email: rajeev_ngri@rediffmail.com
ABSTRACT
Based on an assessment
of the repeat periods of great earthquakes from past seismicity,
convergence rates and paleoseismological results, possible future
source zones of tsunami generating earthquakes in the Indian
Ocean (possible seismic gap areas) are identified along subduction
zones and zones of compression. Central Sumatra, Java, Makran
coast, Indus Delta, Kutch-Saurashtra, Bangladesh and southern
Myanmar are identified as possible source zones of earthquakes
in near future which might cause tsunamis in the Indian Ocean,
and in particular, that could affect India. The Sunda Arc (covering
Sumatra and Java) subduction zone, situated on the eastern side
of the Indian Ocean, is one of the most active plate margins
in the world that generates frequent great earthquakes, volcanic
eruptions and tsunamis. The Andaman-Nicobar group of islands
is also a seismically active zone that generates frequent earthquakes.
However, northern Sumatra and Andaman-Nicobar regions are assessed
to be probably free from great earthquakes (M>8.0) for a few
decades due to occurrence of 2004 Mw 9.3 and 2005 Mw 8.7 earthquakes.
The Krakatau volcanic eruptions have caused large tsunamis in
the past. This volcano and a few others situated on the ocean
bed can cause large tsunamis in the future. List of past tsunamis
generated due to earthquakes/volcanic eruptions that affected
the Indian region and vicinity in the Indian Ocean are also presented.
Science of Tsunami
Hazards, Vol. 27, No. 2, page 32 (2008)
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GEOLOGICAL
EVIDENCE FOR PALEO-TSUNAMIS IN SRI LANKA
Kapila Dahanayake
and Nayomi Kulasena
Department
of Geology, University of Peradeniya,
Peradeniya 20400, Sri Lanka.
(e-mail: kapidaha@hotmail.com)
ABSTRACT
After the 2004 Indian
Ocean tsunami inundation event, thin sediment films of fining
up sequences were located in several topographic depressions
of the southern coastal belt of Sri Lanka. The films consisting
of silty fine sand with particular microfossil assemblages were
located also in closed containers, bottles and kitchen tables.
Well preserved microfossils such as foraminifera, radiolarians
as well as spicules of sponges were noted in these recent tsunami
sediments.
Random augur holes were drilled into some selected depressions
in the southern coastal villages of Peraliya and Denuwala situated
at locations separated by about 50km. In several such holes,
at least two fining up sequences were located below the surface
in soil horizons separated from each other by 35cm to 1m. These
soil profiles were overlying older coral reefs developed on lateritic
formations. The microscopic observations on particular size fractions
of the soil horizons showed microfossil assemblages with textures,
color and organic C contents strikingly comparable to those observed
in the recent tsunami sediments of Sri Lanka. Our findings imply
the occurrence of at least two paleo-tsunami events of different
ages in Sri Lanka originating apparently from a common source.
Science of Tsunami
Hazards, Vol. 27, No. 2, page 54 (2008)
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Last updated: March 2008
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