A prototype earthquake alarm system that can provide early warning of dangerous temblors capitalizes on 'p-waves,' low-energy, usually non-destructive waves that are the first to emanate from the deep underground source of an earthquake. The system is designed to instantly detect an earthquake and estimate its epicenter and magnitude in order to determine the hazard. It could then broadcast a warning to the public. Known as ElarmS, this system can provide up to 40 seconds of warning for major earthquakes.

The deadly 1994 Northridge earthquake caused widespread property damage and took 57 lives. To illustrate how an earthquake alarm system like ElarmS would respond to such an event, the concentric rings show how much warning time would be available for people at various distances from the damage epicenter of the earthquake. The farther from the epicenter, the more warning time is available. But even a few seconds of warning time for those near the epicenter is enough to take protective action.

— Illustrations by Dan Brennan, University of Wisconsin–Madison

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