From the Summary: "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 Ford Island, 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 relevant 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 November 18, 2015, 4 of the United States' 39 DART buoys (10%) were not operational. This figure represents an improvement over the course of the year; in March 2015, 9 of the buoys were not operational (23%). The inoperable stations likely 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."
CRS Report for Congress, R41686
Congressional Research Service: https://crsreports.congress.gov/