People and automated systems in California, Oregon, and Washington receive ShakeAlert EEW alerts only if certain thresholds for magnitude and shaking intensity are met, as identified below. The ShakeAlert system only issues a ShakeAlert Message if the earthquake is expected to produce weak or greater shaking that can potentially produce strong shaking. Depending on their chosen application (e.g. alert delivery to cell phones) USGS-licensed Alert Delivery Partners use a variety of alert delivery thresholds, and may not take action for a given earthquake. USGS recommends that you learn what to expect from the ShakeAlert-powered EEW alerting product and (or) service that you choose to use.
To learn more about earthquake magnitude and intensity and how these thresholds were selected, read the Magnitude, Intensity and ShakeAlert FAQ.