The Tangshan earthquake occurred due to tectonic forces generated by the Amurian tectonic plate interacting with the Eurasian tectonic plate. An earthquake along the 25-mile Tangshan Fault caused a 75-mile rupture under the surface of the ground running north-northeast and south-southwest of the city. Surface faults also opened up in Tangshan itself.
Tangshan is 93 miles east of Beijing in northern China, an area with fairly high seismic activity. Several fault zones run through or near the Tangshan region. From 1966 to 1976, a number of seismic events greater than magnitude 6 occurred near Tangshan, indicating a gradual buildup of activity. At the beginning of 1976, earthquakes of magnitude 5 or 6 were forecast for the Tangshan area.
The Tangshan earthquake struck in the early morning of July 28, 1976, and it lasted about 15 seconds. It registered 7.8 on the Richter scale. An aftershock of 7.1 magnitude followed 16 hours later. The quake demolished 85 percent of the buildings in Tangshan. The official death toll was 242,000, but many estimates range as high as 700,000. In addition, almost 800,000 people were injured. Despite the level of the catastrophe, the Chinese communist government refused international help, even from such neutral agencies as the Red Cross and the United Nations. The political aftermath of the disaster brought an end to the Cultural Revolution and the beginning of a new era of government in China.