The National Tsunami Warning Center (NTWC) is one of two tsunami warning centers in the United States, covering all coastal regions of the United States and Canada, except Hawaii, Guam, the Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands. Until 2013, it was known as the West Coast and Alaska Tsunami Warning Center.

The NTWC, operated by the National Oceanic and Atmospheric Administration (NOAA), detects and analyzes earthquakes worldwide, issuing warnings to local officials in the hazard zones about the advisability of evacuating low-lying coastal areas and moving ships to deep water.

The Pacific Tsunami Warning Center has the responsibility for areas of the U.S. which are not covered by NTWC.

History

Following the March 27, 1964 Alaska earthquake and tsunami, the NTWC (formerly known as The Palmer Observatory) was established in 1967 in Palmer, Alaska, under the auspices of the United States Coast and Geodetic Survey. This earthquake alerted State and Federal officials that a facility was necessary to provide timely and effective tsunami warnings and earthquake information to the coastal areas of Alaska. Congress provided funds in 1965 to construct two new observatories and establish a tsunami warning system in Alaska. The first observatory constructed was at the U.S. Naval Station on Adak Island in the Andreanof Islands in the Central Aleutians. The City of Palmer, in the Matanuska Valley 42 miles northeast of Anchorage, was selected as the site for the primary observatory due to its proximity to bedrock for instrumentation and to communications facilities. Construction of the observatory installations, the task of engineering and assembling the data systems, and the hookup of the extensive telecommunications and data telemetry network was completed in the summer of 1967. With the dedication of the Palmer Observatory on September 2, 1967, the Alaska Regional Tsunami Warning System (ARTWS) became operational.

Originally, the tsunami warning responsibility for Alaska was shared by the three observatories located at Palmer, Adak and Sitka. Sitka, a seismological observatory since 1904, and Fairbanks were the only two seismic stations operating in Alaska in 1964. The responsibilities of Adak and Sitka were limited to issuing a tsunami warning for events occurring within 300 miles of their location. In later years, the responsibility to provide tsunami warning services for Alaska was transferred from the Adak and Sitka observatories to the Palmer Observatory. Sitka and Adak Observatories were eventually closed in the early 1990s, although the seismic instrumentation is still maintained.

In 1973, the Palmer Observatory was transferred to the National Weather Service's Alaska Region and changed its name to Alaska Tsunami Warning Center (ATWC). In 1982, its area of responsibility (AOR) was enlarged to include the issuing of tsunami warnings to California, Oregon, Washington, and British Columbia for potential tsunamigenic earthquakes occurring in their coastal areas. In 1996, the responsibility was again expanded to include all Pacific-wide tsunamigenic sources that could affect the California, Oregon, Washington, British Columbia and Alaska coasts, and the name was changed to the West Coast/Alaska Tsunami Warning Center (WC/ATWC) to reflect those new responsibilities.

In 2003, a new Tsunami Warning Center building was constructed in the yard of the original building. This new facility was the first LEED certified building in the state of Alaska, and within the U.S. Department of Commerce. LEED (Leadership in Energy and Environmental Design) certification is granted by the U.S. Green Building Council, and awards environmentally sensitive construction practices. This new facility provides upgraded power and communications capability, as well as office space for the expanded staff, assuring that the center will continue to provide quality products to the public well into the future.

Following the devastating Indian Ocean tsunami in late 2004, the WC/ATWC expanded its scope to the U.S. Atlantic coast, and the Atlantic coast of Canada. On 1 October 2013, the name was changed to the National Tsunami Warning Center (NTWC) to reflect this expanded geographical zone of responsibility.

Coverage area

NTWC is the tsunami warning authority for the following regions:

Other parts of the United States are covered by the Pacific Tsunami Warning Center.

Overview of operations

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 NTWC detects, locates, sizes, and analyzes earthquakes worldwide. 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.

Alert levels

Deep-ocean tsunami detection

In 1995, NOAA began developing the Deep-ocean Assessment and Reporting of Tsunamis (DART) system. By 2001, an array of six stations had been deployed in the Pacific Ocean.^[3]

Beginning in 2005, as a result of the tsunami caused by the 2004 Indian Ocean earthquake, plans were announced to add 32 more DART buoys to be operational by mid-2007.^[4]

These stations give detailed information about tsunamis while they are still far off shore. Each station consists of a sea-bed bottom pressure recorder (at a depth of 1000–6000 m) which detects the passage of a tsunami and transmits the data to a surface buoy via acoustic modem. The surface buoy then radios the information to the NTWC via the GOES satellite system. The bottom pressure recorder lasts for two years while the surface buoy is replaced every year. The system has considerably improved the forecasting and warning of tsunamis in the Pacific Ocean.