Earthquake Alert vs Tsunami Warning
A quake alert and a tsunami warning are different systems with different timelines. Knowing which is which can save time.
The tracker shows a tsunami flag on some quakes, which often raises a question: is that the same as a tsunami warning? It is not, and the distinction matters near the coast.
The earthquake alert
Earthquake early warning detects shaking that has already begun and sends a notice ahead of the waves. It buys seconds to tens of seconds, useful for dropping and covering or stopping a train. It says nothing about the ocean. This is what systems like ShakeAlert and Japan's warning network provide.
The tsunami evaluation
When an undersea quake is large enough and shallow enough, tsunami warning centers evaluate whether it could displace water into a wave. The tsunami flag on this tracker means USGS marked the event for that evaluation. It is a prompt to check official sources, not a confirmation that a wave is coming.
Official tsunami warnings
Actual warnings come from bodies like the US Tsunami Warning System at tsunami.gov or national equivalents. They issue advisories, watches, and warnings based on the quake plus ocean sensor data. These can arrive minutes to hours before a wave for distant sources, but for a quake just offshore, the first wave may beat any official message.
The rule near the coast
If you are on a coast and feel strong or long shaking, do not wait for an official tsunami warning. Move to high ground immediately, because near-source tsunamis can arrive within minutes. Use the tracker for awareness and context, and treat the natural warning of the shaking itself as your trigger to act.