The 1970 Tonghai earthquake occurred on 4 January 1970 in Tonghai, China.
The rupture originated on the local Yunnan Province’s Red River fault, which had not experienced an earthquake above magnitude 7 since 1700. The earthquake had a magnitude of 7.7 and killed at least 15,000 people, making it one of the deadliest in the history of China. The tremor caused between US$5 to $25 million in damage, felt over an area of 8,781 km (5,456 miles). In Hanoi, North Vietnam, almost 483 km (300 miles) from the epicenter, victims left their homes as the rupture rumbled through the city.
Occurring during the height of the Cultural Revolution, it was not widely publicized by the Chinese government for well over a decade. The amount of aid and finances distributed was described by the Beijing Morning Post as "pathetically small". Much of the aid provided to survivors was in "spiritual" form, including Mao Zedong badges and condolence letters. Nevertheless, the earthquake was among the first to be studied over a long term by the Chinese government. It was cited as one of the reasons behind creating the largest earthquake monitoring system in China, 25 years later.
The July 21 earthquake occurred as the result of strike-slip faulting. Southwestern China is traversed by several major, seismically active, strike-slip faults, and many destructive earthquakes have occurred on lesser strike-slip faults. The epicenter of the July 21 earthquake is about 100 km north-northeast of the large Red River fault and about 100 km west of the large Anninghe fault. The causative fault of the July 21 earthquake has not yet been identified.
In a broad sense, strike-slip faults and earthquakes in southwestern China result from the eastward motion of the Earth's crust that is driven by the collision of the Indian and Eurasian continental plates beneath the Himalaya Mountains and the Tibetan Plateau farther to the west.
Southwest China's Yunnan Province, which is vulnerable to earthquakes, has set up the country's largest earthquake monitoring network.
This year the provincial seismological bureau successfully predicted earthquakes in Menglian County between June 30 and July 12 using information from monitoring stations.
In January of 1970, a quake measuring 7.8 on the Richter Scale hit Tonghai County, and more than 15,000 people died because of lack of a monitoring and forecasting system.