West Coast/Alaska Tsunami
Warning Center
Operations Manual
NOAA/NWS/WCATWC
Palmer,
Section
1.3: Overview of West Coast/Alaska Tsunami Warning Center Operations
Last Updated:
9/2009
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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/watch/advisory 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 center operates 24 hours every day
with two watchstanders on duty. 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
Acquisition and Processing
Tsunami bulletins are initially issued based solely on seismic
data. Approximately 350 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, and 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. The USGS Earthworm software is used as the
system’s 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-wave
data used in the automatic locations through a graphical interface. The initial
magnitude estimate is based on Mb, Ml, or Mwp depending on the earthquake's
size and location. Surface wave magnitude (Ms) processing 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 and the ability to process earthquakes which
occur close in time. 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 messages are issued as soon as an earthquake’s tsunami
potential has been analyzed. The first messages
are based on earthquake magnitude, location, and depth. After the initial message has been issued,
the center monitors recorded tsunami effects and issues supplementary
information. Procedural thresholds for initial messages 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/W indicates that all threatened regions
within 3 hours travel time of the wavefront are placed in a warning or
advisory. User-Defined indicates that
warning regions are chosen by the analyst based on expected zones of highest
threat.
Tsunami history and forecast models 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 advisory, or issue the
warning/advisory for only selected areas, if tsunami history and/or forecast
models indicate 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 (amplitude is defined as the elevation of the wave
above normal sea level). Based on forecasts
determined from observed tsunamis and models, warnings, watches, and advisories
are refined. Warnings are generally
issued for regions with forecasts over 1m and advisories for regions with
forecasts in the range 0.3m to 1m.
Watches are provided as an early alert to areas which may later be
impacted by a wave. Tsunamis can not be forecast
with great precision, so these cut-offs are considered general guidance.
Once a tsunami warning, watch, or
advisory 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 400 sea
level sites throughout the world. Many of these sites are maintained by NOAA's
National Ocean Survey (NOS). In addition to the NOS sites, other agencies such
as the
Products
The WC/ATWC’s product suite has recently been redefined with the
main change regarding the meaning of an advisory. As of February 12, 2008, an advisory will
indicate a tsunami with the potential to create dangerous currents is
possible. Prior to this, an advisory
meant that a warning or watch was issued for another section of the ocean.
The
center issues four types of messages: Warning, Watch, Advisory, and Information
Statement. In short, the messages mean:
Warning -> Inundating
wave possible -> Full evacuation suggested
Watch -> Danger level not yet known -> Stay
alert for more info
Advisory -> Strong
currents likely -> Stay away from the shore
Information -> Minor waves at
most -> No action suggested
The
messages are described in greater detail in Section
5.2.
Tsunami message text includes warning/watch/advisory extent, earthquake
parameters, evaluation, observed tsunami amplitudes, and the tsunami arrival
times (ETA's) for sites throughout the area-of-responsibility. Warning, watch,
and advisory bulletins are updated every 30 minutes in the early parts of an
event and never more than 2 hours apart in the later times.
Messages 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 cell phone text messages.
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 July 2008, 57 U.S. coastal communities
and counties are recognized as TsunamiReady. Center personnel actively work with state and
local emergency officials to attain the TsunamiReady recognition.
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 several new sea level gages have been installed.
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.