In the past 24 hours, three earthquakes occurred in the San Andreas fault system in California, which triggered an emergency warning of "great earthquake" in the scientific community. The fault stretches for more than 800 miles, spanning the north and south of California, and has caused destructive earthquakes many times in history. The first earthquake occurred in the main branch of the Karaoui Lass fault in the northeast of San Francisco, with a magnitude of 2.9; Earthquakes of magnitude 2.5 and magnitude 2.9 occurred successively in another branch of the same fault system and its adjacent area, and no casualties have been reported at present. Experts have called for California to strengthen its preparedness for disaster prevention, and the public should attach great importance to earthquake warning, although the specific occurrence time is difficult to predict.