West Coast/Alaska Tsunami Warning Center
Operations Manual
NOAA/NWS/WCATWC
Palmer,
http://wcatwc.arh.noaa.gov
Section 5.2: Message
Definitions
Last Updated: 2/2004
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Tsunami Warning: Indicates that a tsunami is
imminent and that coastal locations in the warned area should prepare for
flooding. The initial warning is typically
based on seismic information alone. Earthquakes within the WCATWC area of
responsibility (AOR) over magnitude 7.0 trigger a warning covering the coastal
regions within 2 hours tsunami travel time from the epicenter. When the
magnitude is over 7.5, the warned area is increased to 3 hours tsunami travel
time. For earthquakes outside the WCATWC AOR, warnings are only issued for
earthquakes greater than magnitude 7.5 and for those locations within 3 hours
tsunami travel time of the leading edge of the wave. As water level data
showing the tsunami is recorded, the warning will either be cancelled,
restricted, expanded incrementally, or expanded to cover the entire WCATWC AOR
in the event of a major tsunami.
For an example CLICK HERE.
Tsunami
Watch: An alert issued to areas outside
the warned area. The area included in the
watch is based on the magnitude of the earthquake. For AOR earthquakes over
magnitude 7.0, the watch area is 1 hour tsunami travel time outside the warning
zone. For all earthquakes over magnitude 7.5, the watch area is 3 hours tsunami
travel time outside the warning zone. The watch will either be upgraded to a
warning in subsequent bulletins or will be cancelled depending on the severity
of the tsunami.
For an example CLICK HERE.
Tsunami
Advisory: A message issued when the
For an example CLICK HERE.
Tsunami
Information Bulletin: Bulletins issued for
earthquakes less than warning threshold, but greater than 6.5 which are not
likely to trigger a tsunami. Unless
further information is gathered on tsunami generation, only one Tsunami Information
Bulletin is issued for an event.
For an example CLICK HERE.
Tsunami
Information Message: Information messages
issued when smaller earthquakes (greater than magnitude 4.0, but less than 6.5)
may be felt near coastal areas. These
messages are issued to assure coastal residents and emergency managers that
there is no tsunami danger.
For an example CLICK HERE.