USGS ShakeAlert System Reportedly Generated False Earthquake Alert Affecting Nevada and California

On December 4, 2025, the USGS's automated ShakeAlert earthquake detection system erroneously issued a report claiming a magnitude 5.9 earthquake had struck near Dayton, Nevada. The reported false alert triggered emergency warnings on cell phones in parts of California, instructing residents to take protective action. USGS officials said no earthquake occurred and are investigating whether sensor noise or other anomalies caused the system failure.