West Coast/Alaska Tsunami Warning
Center
Operations Manual
NOAA/NWS/WCATWC
Palmer,
Section 1.3:
Overview of the West Coast/Alaska Tsunami Warning Center Operations
Last Updated: 9/2007
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Background
The
West Coast/Alaska Tsunami Warning Center (WCATWC), operated by the Alaska
Region of the National Weather Service and located in Palmer Alaska, is one of
two NOAA Tsunami Warning Centers in the
To accomplish its mission of providing accurate and
timely tsunami bulletins to its area-of-responsibility (AOR) - which includes Canadian
coastal regions, Puerto Rico and the Virgin Islands, and the ocean coasts of
all U.S. States except Hawaii - the WCATWC detects, locates, sizes, and
analyzes earthquakes throughout the Pacific, Atlantic, and Arctic basins. Earthquakes that activate the center’s alarm
system initiate an earthquake and tsunami investigation which includes the
following four basic steps: automatic locating and sizing the earthquake;
earthquake analysis and review; sea level data analysis to verify the existence
of a tsunami and to calibrate models; and disseminating information to the appropriate
emergency management officials.
Tsunami
bulletins are issued to state/province departments of emergency services;
federal disaster preparedness agencies; National Weather Service offices; Canada’s
Atlantic Storm Prediction Center; Federal Aviation Administration offices; the U.S.
Coast Guard; military bases; local emergency managers; United States Geological
Survey offices; and many other recipients located in the U.S. and Canada. Earthquakes
large enough to be felt near the coast, but below the tsunami warning threshold
size, prompt informational statements to the same recipients as warnings to
help prevent needless evacuations.
In
addition to its basic functions, the center conducts a community preparedness
program intended to increase public awareness of the tsunami hazard and improve
tsunami planning at the community level.
The center also actively pursues developmental projects which enhance
tsunami warning operations.
The
WCATWC staff level has recently been increased such that the center operates 24
hours every day with two watchstanders on duty.
The center began 24x7 operations on April 23, 2006. Prior to that, the center operated after
normal work hours on a 5 minute stand-by response basis. Center personnel are notified of activity by
an alarm system which is activated by several methods.
·
Sustained,
strong oscillatory motion at individual seismometers.
·
Activation by
multiple earthquake arrivals observed in sectors of the globe within a specified
time interval.
·
Activation by a
real-time seismic processing system when an earthquake exceeds a predetermined
magnitude threshold for various regions throughout the world.
·
Deep ocean
tsunami sensor detection of an event.
·
Data outages.
Data Acquisition and Processing
Tsunami
bulletins are initially issued based solely on seismic data. Approximately 250 channels of seismic data
are recorded at the center. Seismic
networks which provide the data are operated and funded by many different
agencies, including the United States Geological Survey (USGS), the Global
Seismic Network, the National Tsunami Hazard Mitigation Program, various
universities throughout the country, other national networks, and by the tsunami
warning centers. Access to this data is provided
through dedicated circuits funded by the Tsunami
Hazard Mitigation Program, private satellite networks, or through the
internet. The USGS Earthworm software is used to transfer raw data between the seismological
observatories. See the seismic network
report in Section 2.3 for a
complete description of the WCATWC network.
WCATWC’s seismic processing system, known as
EarlyBird, has been developed and enhanced over the last 25 years. This is
fifth generation of real-time seismic processing systems developed at the center. In this generation, the USGS Earthworm
software is used as a base architecture, and a twelve-monitor PC is used to
support multiple user interfaces. Real-time
seismic data are processed by a P-picker which determines the onset of a P-wave.
An associating/ locating algorithm then uses the P-picks to determine
parameters for local, regional, and teleseismic earthquakes. As more data are
received and processed, the location and magnitude are refined as a watchstander
can add or adjust P data used in the automatic locations through a graphical
interface. The initial magnitude estimate is based on an Mb, Ml, or Mwp
depending on the earthquake's size and location. Surface wave magnitude (Ms) processing
is triggered by the automatic locations, and is computed cycle-by-cycle as
Rayleigh waves arrive at broadband seismometers. Mw magnitudes are also computed from surface
wave spectra and moment tensor inversions. Two identical Windows XP-based PC
systems are active for redundancy, plus for the added ability to process
multiple aftershocks that are common with tsunamigenic earthquakes. A more complete description of this system
can be found in Section 4.1.
As locations are
computed by EarlyBird, they are displayed by a geographic information system (GIS)
known as EarthVu. EarthVu is displayed on
four of the Earlybird monitors and provides the duty scientist with an
interactive tool to compare the present location with historical tsunami and
earthquake data base information. The
GIS has many layers of information which can be displayed on the maps. One of the monitors is dedicated to tsunami
travel time maps automatically created when messages are issued. The EarthVu system also creates maps for
display on the WCATWC web site when
messages are issued, and acts as an interface for pre-computed tsunami model
calibration. See Section 4.3 for more information on
this system.
Procedures
Initial tsunami
bulletins are issued as soon as the earthquake’s tsunami potential has been
analyzed. The first warnings are based on
earthquake magnitude and location. After
the initial bulletin has been issued, the center monitors recorded tsunami
effects and, in coordination with PTWC, issues a cancellation, extension, or
final bulletin as appropriate. Tsunami warning thresholds are shown in the bar
chart below. Warnings with distances
indicate that all coastal regions within that radius are put in a warning. The 3W/3W indicates that warnings are issued
for all areas within 3 hours travel time of the wavefront and watches within 3
to 6 hours. Spec. area indicates that
warning regions are chosen by the analyst based on expected zones of highest
threat.
Tsunami history
and pre-event modeling along with observed tsunami amplitudes are taken into
account when determining the extent of danger for the AOR. WCATWC may refrain
from issuing a warning or issue the warning for only selected areas if tsunami
history (and modeling if available) indicates there is no danger, or danger
only to selected areas. Historical events have shown that tsunami damage is
possible if waves reach 50cm or more in amplitude. Therefore, in most cases if
a tsunami is expected to reach 50cm or more, or if the tsunami potential can
not be accurately judged, warnings are continued. Tsunamis can not be predicted
exactly, so the 50cm cut-off is considered general guidance.
Once
a tsunami warning has been issued, the nearest tide gages and deep ocean tsunami
detectors (DART) are monitored to confirm the existence or nonexistence of a
tsunami, and its degree of severity. The center has access to more than 200
tide sites throughout the Pacific and
Products
There are four
categories of tsunami messages. These are:
Tsunami Warning: Warnings are issued by the TWCs due to
the imminent threat of a tsunami from a large undersea earthquake, or following
confirmation that a potentially destructive tsunami is underway. They may initially be based only on seismic information as a means of providing
the earliest possible alert. Warnings advise that appropriate actions be taken
in response to the tsunami threat. Such
actions could include the evacuation of low-lying coastal areas and the
movement of boats and ships out of harbors to deep waters. Warnings are updated at least hourly or as
conditions warrant to continue, expand, restrict, or end the Warning.
For an example
of the National Weather Service (NWS) format tsunami warning CLICK HERE.
Tsunami Watch: Watches are issued by the TWCs based on seismic
information without confirmation that a destructive tsunami is underway. It is issued as a means of providing advance
alert to areas that could be impacted by a destructive tsunami. Watches are updated at least hourly to
continue them, expand their coverage, upgrade them to a Warning, or end the
alert. A watch for a particular area may
be included in the text of the message that disseminates a Warning for another
area.
For an example
of the NWS format tsunami watch CLICK
HERE.
Tsunami Advisory:
Advisories are issued by the TWCs to coastal populations within areas not
currently in either warning or watch status when a tsunami warning has been
issued for another region of the same ocean.
An Advisory indicates that an
area is either outside the current warning and watch regions, or that the
tsunami poses no danger to that area. The Center issuing the Advisory will
continue to monitor the event, issuing updates at least hourly. As conditions
warrant, the Advisory will either be continued, upgraded to a watch or warning,
or ended.
For an example
of the NWS format tsunami advisory CLICK
HERE.
Information Statement: A text
product issued to inform that an earthquake has occurred and to advise
regarding its potential to generate a tsunami.
In most cases, an Information Statement indicates there is no threat of
a destructive tsunami affecting the issuing TWC’s AOR, and are used to prevent
unnecessary evacuations as the earthquake may have been felt in coastal
areas. An Information Statement may, in
appropriate situations, caution about the possibility of a destructive local
tsunami. A supplemental Information
Statement may be issued if important additional information is received such as
a sea level reading showing a tsunami signal.
An Information Statement may also be upgraded to a watch or warning if
appropriate. Further, the Information
Statement may be used to recommend a warning when protocols agreed to by
emergency management authorities within an AOR so specify.
For an example
of the NWS format information statement CLICK
HERE.
Tsunami warning bulletin text includes warning/watch extent, earthquake
parameters, evaluation, and the tsunami arrival times (ETA's) for sites throughout
the area-of-responsibility. As of August 2005, WCATWC warning and watch bulletins
are updated every 30 minutes.
Bulletins are disseminated by several different methods. The
primary methods are: reading the message over the National Warning System
(NAWAS) circuit, transmission over the NOAA Weather Wire satellite system
(NWWS), transmission over a dedicated Federal Aviation Administration (FAA)
teletype system (NADIN2), and transmission over dedicated National Weather
Service circuits. Messages read over the NAWAS phone are heard by emergency
personnel from the federal to the county levels throughout the AOR, and by the
U.S. Coast Guard stations. The NWWS transmits a printed copy of the message to
the state emergency services, provincial emergency preparedness in
Secondary dissemination
methods are e-mail, web page (http://wcatwc.arh.noaa.gov), phone calls, USGS
dissemination systems, RSS feeds, and digital pager messages.
Since 1980, 12
tsunami warnings have been issued by the WCATWC for events occurring within the
AOR. Response time to issue warnings has
ranged from 5 to 14 minutes with an average response of 9.8 minutes. These warnings all occurred prior to the
center going to a 24x7 operation, and of the 12 warnings only two occurred
during regular work hours. The other 10 occurred
while duty personnel were not on site. Each year the WCATWC staff responds to
more than 250 alarmed events.
Community Preparedness
The ability of any warning system to successfully
save lives and reduce property damage depends upon getting the information to
the public and getting them to respond to the emergency. To help attain this
goal, the National Weather Service has implemented a program known as
TsunamiReady which sets forth guidelines for communities to follow to improve
tsunami preparedness. This program was started in 2000 and was based on the
National Weather Service StormReady program.
The TsunamiReady program's purpose is to recognize communities which
have taken the steps necessary to be as prepared as possible for a tsunami.
This requires the communities to follow a set of guidelines. The guidelines show
that the community can receive and disseminate warnings, have a tsunami hazard
plan in place, have posted evacuation routes, designated shelters, and have worked
to enhance tsunami awareness throughout their community. As of May, 2007, 40
In addition to the
TsunamiReady program, center staff participate in a preparedness effort which
includes: visits to distant coastal communities within the AOR; assisting local
and state jurisdictions in tsunami exercises; visits to local facilities and
schools that are within commuting distance of the center; providing tours of the
center's facilities; and providing tsunami information upon request through the
internet, phone, or mail.
Developmental Projects
Staff members at
the WCATWC are involved in various projects and studies to improve the center’s
services. Some of these are listed below.
1. Automation of
the Tsunami Warning System: this is an ongoing project to develop the necessary
techniques and implementing them into an expert computer system to locate and
analyze earthquakes, and to rapidly disseminate that information to the
recipients in the TWS.
2. Magnitude
studies: another ongoing project to rapidly determine the size of an event and
to relate it to the event’s tsunamigenic potential.
3.
Instrumentation: equipment upgrades at the center and the remote sites so that
the most reliable and efficient set-up is maintained. This involves
considerable on-site equipment design and development for special adaptive
purposes. Remote seismic sites have all been upgraded from analog to digital,
VSAT telemetry, and more new sea level gages are planned for installation.
4. Modeling: tsunami
generation, propagation, and inundation computer modeling studies are being
developed, tested, and utilized at the center. Tsunami wave heights are now
estimated at locations outside the source zone based on predetermined tsunami
models and recorded wave heights. These estimated heights are used in warning
extension or cancellation. The modeling
effort also helps the center determine beforehand which areas are threatened by
certain events.
5. Improved
information and warning products: new public products have been developed to
make warnings and informational messages easier to read and understand.
6. Web site: WCATWC
has designed an internet web site for public education and message access. This
site is continually being upgraded and is used extensively after large events.
It has proven an excellent method to issue public information.