The Warning System

PTWC

Brian Shiro, geophysicist at the PTWC.

Earthquake

Seismographs record earthquake waves that travel through the earth.

The Pacific Tsunami Warning Center (PTWC) provides warnings of tsunamis to the public and to organizations responsible for public safety in coastal areas of Hawai'i (since 1949), the Pacific Ocean (since 1965), the Indian Ocean (since 2005), and the Caribbean Sea (since 2006). Scientists at the Center rapidly detect phenomena that cause tsunamis and assess their tsunami potential. They detect and monitor tsunamis when they occur, predict when they will arrive at affected coastlines, and continue to provide updated information about tsunamis throughout their duration. (Information from Dr. Gerard Fryer, PTWC)

Scientists are always on the alert for the next tsunami event. When an earthquake occurs, instruments called seismographs record the seismic (earthquake) waves that travel through the earth. Scientists at PTWC and other tsunami warning centers monitor seismographs around the world to see if the earthquake is large enough to possibly cause a tsunami.

DART siren

The sirens are tested on the first working Monday of each month at midday.

Scientists then monitor special deep-sea gauges that record the passage of actual tsunami waves in the deep ocean. Since tsunami waves travel through the entire water column, these pressure sensors will detect the waves. These instruments are called DART buoys, which stands for "Deep-ocean Assessment and Reporting of Tsunamis."

The deep-sea gauges send information from a surface buoy through satellites to the warning centers. Scientists use this information in addition to forecast models. The availability of seismic data to rapidly locate and characterize earthquakes, as well as improved access to sea level data helps scientists to confirm and measure tsunamis.

The speed at which tsunami waves travel is affected by the depth of the ocean. Because scientists know the depth of the ocean, they can predict how fast the waves will travel and therefore how long it will take them to reach us.

When scientists at the warning centers are certain that a tsunami is approaching, they will issue a tsunami warning and sirens will sound. When the sirens sound, everyone in a tsunami evacuation zone should listen to Civil Defense instructions on the radio or TV and if necessary, evacuate in order to be safe. If you live outside of a tsunami evacuation zone, stay where you are.*

*Some text excerpted from "Tsunami Safety Booklet."

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Last Revised September 2013