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:
10/2011
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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 worldwide.
Earthquakes that activate the Centers 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; the Canada 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. The Center records approximately 500
channels of seismic data. 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, various universities throughout the country, other national
networks, and by NOAA. Access to these
data is provided through dedicated circuits funded by the National Weather Service,
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 seismic network.
WCATWCs seismic processing system,
known as EarlyBird, has been developed and enhanced over the last 25 years. 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 as well as magnitude parameters. An associating/
locating algorithm then uses the P-picks to determine source 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 earthquakes tsunami
potential has been determined. The first
messages are based on earthquake magnitude, location, and depth.
After the initial message has been issued,
the Center monitors sea level networks 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.
User-Defined indicates that warning regions
are chosen by the analyst based on expected zones of highest threat.
Further information on procedures used at the
WCATWC can be found in NWS
Instruction 10-701.
Tsunami history and forecast models along with observed tsunami heights
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 ambient 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
(DARTs) are monitored to confirm the existence or nonexistence of a tsunami,
and its degree of severity. The Center has access to more than about 500 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 University of Hawaii Sea Level Center, the Canadian Hydrographic Survey,
and the Japanese Meteorological Agency provide sea level information to the Center.
Thirty-nine DARTs have been installed by the
National Weather Service’s National Data Buoy Center.
Sea level data arrives mainly through
dedicated NWS circuits which transmit data downloaded through GOES satellite
transmissions. Data arrives in many
formats and is decoded locally, then displayed for analysis by the program
TideView. Further information on the
sea-level network is available in section
2.4.
Products
The
Center issues four types of messages: Warning, Watch, Advisory, and Information
Statement. In short, the messages mean:
|
Alert
Level |
Threat |
Action |
|
Warning |
Inundating wave possible |
Full evacuation suggested |
|
Advisory |
Strong currents likely |
Stay away from the shore |
|
Watch |
Danger level not yet known |
Stay alert for more info |
|
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, recommended
actions, earthquake parameters, observed tsunami amplitudes, and tsunami
forecasts 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), 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 text message to
state warning points, provincial emergency preparedness in British Columbia,
Canada, and to National Weather Service (NWS) offices. The NWS offices forward
the message to NOAA Weather Radio, the Emergency Alert System, the Emergency
Managers Weather Information Network, the Global Telecommunications System, and
other communication systems available to the public and media.
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 delivering the information to the public and persuading 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 October 2011, 92 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 preparedness efforts which include: training
other agencies who support tsunami preparedness, visits to 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 Centers 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: rapidly determine the size of an event and
to relate it to the events 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 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: 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.