Earthquake early warning systems don’t predict earthquakes. Instead, they detect ground motion as soon as an earthquake begins and quickly send alerts that a tremor is on its way, giving people crucial seconds to prepare.
In 1985, Caltech seismologist Tom Heaton published the first paper on the concept of earthquake early warning systems, which are networks of ground-based sensors that send alerts to users when the earth begins to tremble.
Such systems, including ShakeAlert on the West Coast of the United States, operate on the principle that while seismic waves travel at just a few miles per second, electronic alerts from the region of the epicenter can be sent almost instantly. Here's how it works:
During an earthquake, several types of seismic waves radiate out from the quake's epicenter. First, weaker but faster-moving P waves trigger sensors that, in turn, transmit signals to data processing centers.
Algorithms quickly estimate the earthquake's location, magnitude, and intensity: Where is it? How big is it? Who is going to feel it?
The system then sends an alert before slower but more destructive S waves and surface waves arrive.
Although people who are near the epicenter will have little, if any, advance warning, those farther away may have critical seconds to brace for shaking. Paired with automated responses that can slow trains or shut off gas lines, early warning systems may help prevent some of the injuries and damage typically associated with major quakes.
An earthquake just happened. Why didn't I receive an alert on my smartphone?
You might be too close to the epicenter. In California, early warning alerts are typically delivered five to eight seconds after an earthquake starts. That's the time it takes for seismic waves to travel to the closest stations and for computers to analyze the data. If you are less than 10 miles from the epicenter, it is unlikely you will get a warning before you start feeling significant shaking.
The shaking might not have been strong enough. It is important to remember that most people experience weak shaking during an earthquake. This is because large earthquakes are rare, and because individuals are often too far from the epicenter to experience significant shaking. While a small earthquake can cause strong shaking near its epicenter, there is not enough time for early warning systems to detect, process, and deliver alerts before the shaking has already begun in those locations. As scientists and public officials continue to tune the system's parameters, the threshold for an alert could be lowered.
Your phone settings may need adjustment. Some earthquake early warning systems require users to turn on location settings or enter a specific home location. Emergency alerts may not override "Do Not Disturb" settings unless allowed. Alert delivery typically occurs faster through Wi-Fi than through cellular networks, so connecting to Wi-Fi networks when possible is recommended.
