"The National Oceanic and Atmospheric Administration's (NOAA's) National Weather Service (NWS) manages two tsunami warning centers that monitor, detect, and issue warnings for tsunamis. The NWS operates the Pacific Tsunami Warning Center (PTWC) at Ewa Beach, Hawaii, and the National Tsunami Warning Center (NTWC) at Palmer, Alaska. The tsunami warning centers monitor and evaluate data from seismic networks and determine if a tsunami is likely based on the location, magnitude, and depth of an earthquake. The centers monitor coastal water-level data, typically with tide-level gauges, and data from NOAA's network of Deep-ocean Assessment and Reporting of Tsunamis (DART) detection buoys to confirm that a tsunami has been generated or to cancel any warnings if no tsunami is detected. As of January 20, 2015, 12 of the United States' 39 DART buoys were not operational. According to NOAA, the inoperable stations would not prevent the issuance of tsunami warnings, which are primarily a function of seismic data from an earthquake or landslide, combined with location information about the event. However, lacking these stations could mean the warnings encompass a larger area than would be the case if all stations were operating, and it could lengthen the time a warning remains in effect."
CRS Report for Congress, R41686