The tsunami in Samoa Tuesday was a disaster that could have been much worse were it not for the tsunami warning system that forecast the timing and size of the waves with great accuracy. Using mathematical models, geophysicists were able to predict that there was little danger of a tsunami in the Hawaiian Islands and prevented the cost and chaos of sirens and evacuations.

Forecasting the propagation of a tsunami is a science that has advanced tremendously since the tragic magnitude-9.1 tsunami of Dec. 26, 2004, that killed a quarter of a million people around the rim of the Indian Ocean.

The Samoa tsunami was generated by a magnitude-8.1 earthquake and released only about 3 percent as much energy, causing a much smaller tsunami that still produced devastating effects due to the low elevation of the island.

Advances in tsunami measurement and numerical modeling are being integrated to create an effective tsunami forecasting system that was beyond possibility even five years ago. Computer models can create animation of the propagation with estimates of wave height using sea floor topography in the models.

Neither technology can do the job alone.

DART (Deep-ocean Assessment and Reporting of Tsunamis) real-time tsunami monitoring systems, developed by the Pacific Marine Environmental Laboratory (PMEL), are positioned at strategic locations throughout the ocean and play a critical role in tsunami forecasting.

A DART system consists of a sea floor bottom pressure recording (BPR) system capable of detecting tsunamis as small as 1 centimeter in the open ocean, and a moored surface buoy. An acoustic link transmits data from the BPR on the sea floor to the surface buoy, which then relays the data via a GOES satellite link to ground stations for immediate dissemination to the National Oceanic and Atmospheric Administration's Tsunami Warning Centers and PMEL.

The NOAA Center for Tsunami Research has developed a database of tsunami propagation models that have been pre-computed for tsunami source events at selected locations along known and potential earthquake zones.

The pre-computed events can be combined to simulate arbitrary earthquake scenarios to provide a fast forecast during an actual tsunami event. The accuracy of the propagation database has been validated by comparison with data from 17 tsunamis, eight of which were assessed in real time.

The propagation database can forecast offshore tsunami wave heights at any specified location in the Pacific, Atlantic and Indian oceans.

Learn more about DART at nctr.pmel.noaa.gov/Dart/index.html, and see animation of the tsunami propagation at nctr.pmel.noaa.gov/samoa20090929/20090929_samoa_a.mov.