#shakealert

#shakealert

Thousands of Californians received earthquake warnings on Thursday after a 4.7-magnitude tremor shook Northern California. The US Geological Survey (USGS) issued a ShakeAlert after the quake struck at 4:49am PT (7:49am ET), about 70 miles offshore of Petrolia. ShakeAlert messages are triggered when seismic sensors detect a quake of magnitude 4.5 or higher expected to cause significant shaking. The epicenter was located 190 miles west of Chico, a city of about 121,000 residents, and 65 miles west-southwest of Fortuna, which has roughly 12,000 residents.

The ShakeAlert early warning system aims to provide people with precious seconds to react, reducing the risk of injury during earthquakes by detecting P-waves.