Earthquake early warning does not predict earthquakes. It detects the fast, harmless P-wave at stations near the epicentre and sends an alert before the slower, damaging S-wave arrives.
That gives you a head start measured in seconds — enough to drop under a table, stop a lift, halt a train, or pause surgery. It is not enough to evacuate a city.
Lead time depends on distance from the epicentre. Directly above the rupture there may be no warning at all. The further you are, the more warning you get, but the weaker the shaking.
Public feeds such as USGS and BMKG publish events after they are located, typically within one to five minutes. Those are situational awareness, not early warning. Treat the two as different products.
SeisAlert shows an estimated S-wave arrival time for your saved locations so you can see how much time the physics allows.
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