At 7:36 p.m. on 4 February 1975, a magnitude 7.3 earthquake struck Haicheng, an industrial city in China's Liaoning province, rupturing a fault segment roughly 54 km long at a depth of about 15.6 km. Around 90% of the city's structures were significantly damaged or destroyed.
What made Haicheng different was the days before the quake. A pronounced foreshock sequence from 1-3 February, combined with reports of anomalous animal behaviour, groundwater changes and shifts in electrical resistivity, convinced Chinese seismologists to issue a formal warning. Local authorities ordered a mass evacuation, moving people out of buildings and into the open.
The evacuation is credited with preventing an estimated 150,000 additional deaths, making it the only time in recorded history that a major earthquake was successfully predicted and acted upon in advance at this scale. The warning came at a cost, however: hundreds of evacuees froze to death in improvised winter shelters, since many had been moved into unheated tents during a harsh Liaoning winter.
The success bred over-confidence: when a magnitude 7.6 earthquake struck Tangshan barely 18 months later, in July 1976, none of the same warning signs appeared beforehand and no evacuation was ordered. Tangshan killed an officially confirmed 242,000 people — a reminder, catalogued by USGS and Chinese seismological records, that the Haicheng prediction relied on a rare, unusually strong foreshock pattern that most large earthquakes never produce.