How are tsunami early warnings issued?

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Inundation at Pago Pago, American Samoa, from the 2009 Samoa tsunami. Image Credit: NOAA/NGDC

In the U.S., tsunami early warnings are issued by two warning centers operated by the National Weather Service. The National Tsunami Warning Center (NTWC) monitors for earthquakes and issues tsunami advisories, watches, warnings, and information statements for Alaska, the U.S. mainland, U.S. Atlantic and Gulf of Mexico, Canada, and U.S. interests in the Caribbean (Puerto Rico and the U.S. Virgin Islands)[1,2,3]. The Pacific Tsunami Warning Center (PTWC) provides similar services to Hawaii, almost every country around the Pacific Ocean, most Pacific island states, nations bordering the South China Sea, other U.S. interests, and many countries in the Caribbean[3]. In the Indian Ocean, warnings are provided by regional services in Australia, India, and Indonesia[3].

To provide alerts as early as possible, initial tsunami warnings are usually based only on seismic information that detects the earthquake’s location and magnitude[4,5]. Information from coastal sea-level gauges and offshore buoy stations confirms the existence or absence of a tsunami[6]. Then, information from seismic data, sea-level gauges, and buoy stations are used to generate models that forecast tsunami arrival times and estimate coastal impacts[6]. The models help warning centers update or cancel warnings as they learn more about the earthquake and resulting tsunami[6].

In the U.S., warnings are sent to coastal National Weather Service offices and emergency and local management officials[1]. Multiple lines of communication, such as the Emergency Alert System[7] and sirens, are used to notify the public and encourage people to evacuate low-lying coastal areas.

In the U.S., state geological surveys and the U.S. Geological Survey (USGS) help to conduct research to determine where tsunamis have occurred in the past, and where high-risk areas are located. The USGS partners closely with the National Oceanic and Atmospheric Administration (NOAA) through the NOAA Center for Tsunami Research, and has upgraded tsunami detection technology (seismographs) through the National Tsunami Hazard Mitigation Program[8].


How does the tsunami warning system work? National Oceanic and Atmospheric Administration
Tsunami Warning Center History National Weather Service
PTWC Responsibilities National Weather Service
Pacific Tsunami Warning Center Frequently Asked Questions National Weather Service
How do seismometers contribute to a tsunami warning system? U.S. Agency for International Development
NOAA Tsunami Program National Oceanic and Atmospheric Administration
Emergency Alert System (EAS) Federal Communications Commission
About Tsunami and Earthquake Research at the USGS U.S. Geological Survey

Learn More:

  • National Tsunami Warning Center (Interactive Map), National Weather Service
    Map of active tsunami watches, warnings, and advisories in effect in the United States and territories
  • Pacific Tsunami Warning Center (Interactive Map), National Weather Service
    Map of tsunami watches, warnings, and advisories in effect in the Pacific Ocean and Caribbean Sea. For Indian Ocean tsunami information, see the following websites from regional service providers: Australia, India, Indonesia