Four alert levels, and they do not mean the same thing. Here is what each one means, who issues it, and exactly what to do when you hear it.
The most serious tsunami alert: a dangerous tsunami with widespread flooding is expected or already happening.
Significant inundation is expected. Powerful currents and flooding can continue for many hours, and the first wave is often not the largest.
Move immediately to high ground or as far inland as you can. Do not wait to see the water, and do not return until officials say it is safe.
A tsunami is possible. A distant earthquake has occurred and the threat to your coast has not yet been ruled out.
Officials are still evaluating sea-level data. A watch is either upgraded to an advisory or warning, or cancelled, usually within hours.
Stay alert and stay tuned to official channels. Review your evacuation route now so you are ready to move if it is upgraded.
A tsunami with strong currents or waves dangerous to those in or very near the water is expected or occurring.
Widespread inland flooding is not expected, but harbours, beaches, marinas and river mouths become genuinely dangerous. Advisories are the level people most often underestimate.
Get out of the water and stay off beaches and away from harbours. Boats in harbours are at particular risk from the currents.
An earthquake has occurred, but there is no tsunami threat, or the threat is still being evaluated.
Usually issued to stop speculation after a large earthquake that will not generate a damaging tsunami. It is reassurance, not a call to act.
No action needed. It is worth reading so you know why no alert followed a quake you may have felt.
QuakeMate relays official alerts and does not issue its own. Always follow instructions from your local authorities and national tsunami warning centre.
The first alert is based on the earthquake alone - its magnitude, depth and location - because that is all anyone has in the first minutes. As deep-ocean buoys and coastal tide gauges report real wave heights, the alert is revised: a watch is upgraded to an advisory or a warning, or cancelled outright.
A tsunami is a series of waves. The first is frequently not the largest, and dangerous currents can continue for many hours after it arrives. This is why an alert stays in force long after the first wave, and why a quiet sea is not the all-clear. Wait for officials to cancel it.
Pacific Tsunami Warning Center (PTWC)
Pacific basin, Caribbean and, as a service provider, the Indian Ocean.
US National Tsunami Warning Center (NTWC)
Continental United States, Alaska and Canada, distributed through the National Weather Service.
Regional warning systems
The Indian Ocean and the North-Eastern Atlantic, Mediterranean and connected seas run their own coordinated systems under UNESCO/IOC.
National agencies
Countries such as Japan, Chile and Indonesia issue their own alerts, which are usually faster for their own coastline than any international centre.
A tsunami warning is the most serious: dangerous, widespread coastal flooding is expected, and you should move to high ground immediately. An advisory means strong currents and waves dangerous in or near the water, but not widespread inland flooding - get out of the water and off the beach. A watch means a tsunami is possible and officials are still evaluating, so stay alert and be ready to move.
Yes. An advisory is the level people most often underestimate. It means currents strong enough to sweep swimmers, surfers and small boats are expected in harbours, beaches and river mouths, even though buildings inland are not expected to flood. Most tsunami injuries during advisories happen to people who stayed in or near the water.
For the Pacific and Caribbean, the Pacific Tsunami Warning Center and the US National Tsunami Warning Center issue alerts, distributed through the National Weather Service. Other basins are covered by regional centres such as the Indian Ocean and North-Eastern Atlantic and Mediterranean tsunami warning systems, alongside national agencies. QuakeMate relays official alerts from these sources rather than issuing its own.
Until officials cancel it. A tsunami is a series of waves that can arrive over many hours, and the first wave is frequently not the largest, so a warning commonly stays in force long after the initial wave. Never treat the first wave, or a lull between waves, as the end of the event.
Yes, and both are routine. A watch is often upgraded to an advisory or a warning as sea-level gauges and deep-ocean buoys report real wave heights, or cancelled once the threat is ruled out. Alert levels are revised as measurements replace the initial earthquake-based estimate.
No. Generating a tsunami usually needs a large, shallow earthquake that displaces the sea floor vertically, typically magnitude 7.0 or above under or near the ocean. Many large quakes are too deep, too far inland, or move the ground sideways rather than vertically, which is why an information statement often follows a quake that was widely felt.
Live warnings, recent tsunami-capable earthquakes and coastal risk for each country.
QuakeMate pushes tsunami-capable earthquakes and official alerts to your phone the moment they are published.
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