The phone app warns users to “drop, cover, and hold on” if they are likely to experience shaking intensity of at least three out of a maximum 10 in a magnitude 4.5 or higher earthquake. Many people will feel a quake with a level-three shaking intensity, according to researchers.
USGS calculates that California has a 99.7% chance of being struck by at least a 6.7 magnitude earthquake within the next 30 years.
The system alerts people a few moments before a quake can be felt so they can prepare. It uses numerous seismic stations to detect the start of an earthquake and rapid communications to send the data to computers that instantly calculate location, magnitude and intensity of shaking, creating alerts for distribution to areas within the quake zone. The system does not predict earthquakes.
Warnings produced by the ShakeAlert system are also pushed through the same wireless notification system that issues Amber Alerts.
After years of sluggish progress in developing the early-warning system, Gov. Gavin Newsom unveiled MyShake statewide last year to coincide with the 30th anniversary of the Loma Prieta earthquake, which ravaged the San Francisco Bay Area on Oct. 17, 1989.
The test on Thursday coincided with the Great California ShakeOut safety drill, which occurs on the third Thursday of October each year.