Earthquake Early Warning vs. USGS Alerts: What's the Difference?

People often confuse Earthquake Early Warning (EEW) with post-earthquake alerts. Both come from the USGS. Both send notifications to your phone. But they do different things, and understanding the difference matters if you actually want to be prepared.

What is Earthquake Early Warning (ShakeAlert)?

ShakeAlert is a real-time warning system operated by the USGS across California, Oregon, and Washington. When a large earthquake begins, seismic sensors detect the first, faster-moving P-waves. The system estimates the size and location almost instantly, then sends warnings ahead of the slower, more damaging S-waves.

How much warning? It depends on how far you are from the epicenter. If you are directly over it, zero to a few seconds. If you are 60 miles away, maybe 20 seconds. If you are 100+ miles away in a Cascadia scenario, potentially a minute or more.

What can you do in a few seconds? Drop, cover, and hold on before the shaking starts. That is exactly the window that matters — enough time to get under a desk, out of a doorway, or off a ladder.

ShakeAlert is delivered through:

• Wireless Emergency Alerts (WEA) on your phone — nationwide, no signup needed
• MyShake app — free, from the USGS partner UC Berkeley
• Google's built-in Android earthquake alerts
• Apple's built-in iOS earthquake alerts (in supported regions)

What are USGS post-quake alerts?

These are the alerts that come after an earthquake has been detected and measured. The USGS Earthquake Notification Service (ENS) sends emails when an earthquake meets criteria you set — magnitude threshold, geographic region, and so on.

These alerts typically arrive 2 to 10 minutes after the event. Not for taking cover — for knowing what happened and where. Useful for family members, first responders, journalists, and anyone monitoring a region.

The USGS also publishes real-time data via GeoJSON feeds and their public earthquake map. Third-party apps and websites (including TerraSentri) pull from these feeds to provide monitoring.

The gap neither system fills

Here is the scenario neither ShakeAlert nor USGS ENS handles well: you live in San Diego. Your mom lives in Sacramento. A 6.2 hits north of her city.

ShakeAlert will not alert you. You are not in the shaking zone. It only warns people who will actually feel the quake in the next few seconds.

USGS ENS could alert you, but only if you specifically set up alerts for Sacramento. And it sends an email, not a push notification, so you might not see it for hours.

What you actually need in this moment is a push notification that says: "M6.2 earthquake — 15 km from Mom's Home (Sacramento). Location currently: unable to verify." Within minutes. On your phone. Loud.

That is not what ShakeAlert or USGS ENS do. That is what apps like TerraSentri do — they let you save multiple locations and send targeted push notifications when any of them are affected.

Which do you actually need?

Everyone in California, Oregon, or Washington should have ShakeAlert enabled. It is free, it is built into your phone in most cases, and it can save your life. Do this today.

If you only care about your own current location, USGS ENS or the native phone alerts are enough. ShakeAlert warns you before shaking, WEA tells you an event happened.

If you have family in multiple cities, or you live in a US city while parents are overseas, you need location-based monitoring. Save every location you care about. Get one alert per affected place. Know exactly which family member might have felt what.

The three systems complement each other. ShakeAlert saves you seconds when it matters most. USGS alerts confirm what happened. A location-monitoring app tells you about the people you cannot see.