USGS Issues First Quake Alert

The first earthquake alert to be issued by USGS was triggered by last night's 4.6 earthquake in southern California. Image: Weatherboy — The first earthquake alert to be issued by USGS was triggered by last night’s 4.6 earthquake in southern California. Image: Weatherboy

USGS issued their first Shake Alert through the Wireless Emergency Alert (WEA) system during yesterday’s 4.6 earthquake which struck near Barstow, California. USGS deployed the alert to those in the area that could feel a magnitude 4 or greater quake.

ShakeAlert initial earthquake location (black dot). Star is regional network epicenter. MMI 4 polygon is the estimated initial alert area. Red circle is front of peak shaking when the alert was released. Shaking takes 10 s to expand from circle to circle.

USGS is rolling-out the system to alert people in a potential impact area of the quake. The WEA system would usually be used for quakes with a magnitude of 5.0 or greater. Because the quake was initially rated a 5.1, in the interest of time, the alert was issued within 7 seconds of the quake to the impact area.

The earthquake happened just after 7pm local time and for some, the alert came in as the quake started or just before.