The Science Behind Tsunami Detection

To help identify and predict the size of a tsunami, scientists look at the size and type of the underwater earthquake that precedes it. This is often the first information they receive, because seismic waves travel faster than tsunamis.

This information is not always helpful, however, because a tsunami can arrive within minutes after the earthquake that triggered it. And not all earthquakes create tsunamis, so false alarms can and do happen.

That’s where special open-ocean tsunami buoys and coastal tide gauges can help—by sending real-time information to tsunami warning centers in Alaska and Hawaii. In areas where tsunamis are likely to occur, community managers, educators, and citizens are being trained to provide eyewitness information that is expected to aid in the prediction and detection of tsunamis.

In the United States, the National Oceanic and Atmospheric Administration (NOAA) is responsible for reporting tsunamis and is in charge of the Center for Tsunami Research.

Detecting a Tsunami

Following the Sumatra Tsunami in 2004, NOAA stepped up its efforts to detect and report tsunamis by:

• Developing tsunami models for at-risk communities
• Staffing NOAA warning centers around the clock
• Expanding the warning coverage area
• Deploying Deep-ocean Assessment and Report of Tsunamis (DART) buoy stations
• Installing sea-level gauges
• Offering expanded community education through the TsunamiReady program

The DART system uses seafloor bottom pressure recorders (BPRs) to register the temperature and pressure of ocean water at regular intervals. This information is relayed via surface buoys and GPS to the National Weather Surface, where it is analyzed by experts. Unexpected temperature and pressure values can be used to detect seismic events that can lead to tsunamis. Sea-level gauges, also known as tide gauges, measure ocean levels over time and help confirm the effects of seismic activity.

For tsunamis to be detected quickly and reliably, BPRs must be placed in strategic locations. It is important that the devices are near enough to potential earthquake epicenters to detect seismic activity but not so close that that activity disrupts their functioning.

Although it has been adopted in other parts of the world, the DART system has been criticized for its high failure rate. The buoys frequently degrade and stop functioning in the harsh marine environment. Sending a ship to service them is very expensive, and non-functioning buoys are not always replaced promptly.

Detection Is Only Half the Battle

Once a tsunami is detected, that information has to be communicated effectively and rapidly to vulnerable communities. In the event that a tsunami is triggered right along the coastline, there is very little time for an emergency message to be relayed to the public. People living in earthquake-prone coastal communities should view any large earthquake as a warning to act immediately and head for higher ground. For earthquakes triggered farther away, the NOAA has a tsunami warning system that will alert the public via news outlets, television and radio broadcasts, and weather radios. Some communities also have outdoor siren systems that can be activated.

NOAA's guidelines inform the public on how to respond to a tsunami warning. To see where tsunamis have been reported, check NOAA’s interactive map of historical tsunami events.