Earthquake early warning: ShakeAlert and MyShake
Early warning is not prediction. It detects an earthquake that has already started and races a message ahead of the shaking. That buys seconds — sometimes tens of seconds — and seconds are enough to get under a table, stop a train, or close a valve.
QuakeIndex is not an alerting service and cannot warn you. We report what has been recorded, usually within a minute. This page is about the systems that do warn, and how to be on them.
How it can possibly work
Seismic waves travel at a few kilometres per second. A message travels at the speed of light. So if instruments near the epicentre detect the first, faster P-waves and a system decides within a second or two that a significant earthquake has begun, the warning can outrun the slower, damaging S-waves to places further away.
The trade-off is built into the physics: the closer you are to the epicentre, the less warning you get, and directly above it you get none. The places that will shake hardest are the places warned last. That is a limit of the method, not a flaw in the implementation.
ShakeAlert
ShakeAlert is the USGS-operated system for California, Oregon and Washington. USGS does not send alerts to the public directly; it produces the ShakeAlert message and partners deliver it. For an individual that means two routes:
- Wireless Emergency Alerts (WEA) — the same channel as an AMBER alert. No app required, no setup, and it arrives on essentially any modern phone. The trade-off is that WEA has a delivery threshold, so it is used for stronger expected shaking rather than for everything.
- An app — MyShake, or other ShakeAlert-powered apps. These can alert at lower shaking thresholds than WEA, so you will hear about more events.
Android phones in the covered states also have Android Earthquake Alerts, which is built into the operating system. Check your phone's settings rather than assuming either way.
MyShake
MyShake is a free app from the Berkeley Seismological Laboratory that delivers ShakeAlert warnings and, separately, uses phone accelerometers as a distributed sensing network. It is free, it does not sell data, and it is the simplest way to get alerts at a lower threshold than WEA.
What to do with the seconds
Whatever you can do in the time you get. Which, honestly, is usually: drop, cover and hold on — getting into position before the shaking arrives rather than during it. That is a genuine reduction in injury risk, and it is most of the value.
The larger value is institutional: automated systems act on ShakeAlert without a human in the loop. Trains slow, lifts stop at the nearest floor and open, surgeries pause, and industrial processes shut down safely. That is where the seconds do the most good.
Outside the three states
ShakeAlert covers California, Oregon and Washington. Alaska, Hawaii, Nevada, Utah and the rest of the seismically active United States have no public early warning system — it needs a dense instrument network and it has been built out where the exposure is greatest. If you are elsewhere, preparation is the available lever: a kit and a retrofit if your house needs one.
What to expect, honestly
- Missed alerts happen. An earthquake directly beneath you will not be warned in time. That is physics.
- False alerts happen. Deciding in one second whether a signal is a significant earthquake is genuinely hard, and the system is tuned to accept some false positives rather than miss real events.
- The estimated magnitude in an alert may be wrong. It is computed from the first seconds of data and gets revised afterwards, like every other magnitude.
None of that is a reason not to enable it. It is a reason not to be surprised.
Sources
Last checked:
- ShakeAlert earthquake early warning system — USGS and partners
- How ShakeAlert works, and how to receive alerts — USGS
- MyShake — Berkeley Seismological Laboratory
- Wireless Emergency Alerts — FCC