What caused the Tangshan earthquake?

The Tangshan earthquake was caused by the shift of faults located under the city, such as the Tangcheng-Lijiang fault. Northern China has a high level of seismic activity and, in 1974, scientists predicted a large earthquake would hit the region within 2 years. The Tangshan earthquake occurred on July 28, 1976.

The Tangshan earthquake occurred at 3:42 a.m. local time and lasted approximately 15 seconds. It measured 7.8 on the Richter scale. A 7.1 aftershock occurred in the region 16 hours later. The Tangshan earthquake caused approximately 242,769 deaths and destroyed the city of Tangshan. As of May 2015, it is considered the second deadliest earthquake in the world.