[7]) This "occurred on a near-vertical right-lateral strike-slip fault, striking N40°E",[8] the block on the southeast side sliding about 3 metres (9.8 ft) to the southwest.

[11] The second main shock, with a magnitude 7.0 Mw , or 7.4 Ms , struck that afternoon at 18:45:36 near Luanxian, about 70 kilometres (43 mi) to the east-northeast ("B" on the intensity map in the next section), just south of the northeastern end of the Tangshan fault.

[13] The first of these struck just three and a half hours after the initial shock, at 7:17, at the southern end of Tangshan fault, near Ninghe ("C" on the map in the section below),[14] with a magnitude of 6.2 Ms .

[16] As a result, Tangshan was "mainly a city of unreinforced brick buildings",[6] sitting right on top of a major fault line.

The power (magnitude) of the Tangshan earthquake is indicated by the extent of where it was felt: up to 1,100 km (680 miles) away, across most of northeastern China, and even in Mongolia and Korea.

Nearly every building and structure in the city collapsed, wholly or partially, infrastructure was severely damaged, and essential services such as electric power, water supply, and communications were entirely knocked out.

Further out (to the outer orange contour), and around the city of Tianjin and a few isolated patches, intensity VIII shaking mostly affected Class I buildings (more than half destroyed), bridges, and tall brick chimneys.

For the most part the mine roadways (tunnels) were not seriously damaged, but with the loss of electrical power there was no illumination (aside from headlamps), no ventilation, and no working lifts.

[34] However, de-watering, overhauling of flooded electrical equipment, and rebuilding of surface buildings and structures continued for a year and a half; the pre-earthquake level of production was not reached until the end of 1977.

These vital arteries (and other railways and branch lines) were seriously damaged by the earthquakes, mainly in the areas of intensity IX or greater shaking.

Conversely, bridges and rails in Tangshan City, built on dense soil with a deep water table, were largely undamaged even though subject to intensity XI shaking.

Within days, Pararas-Carayannis, an oceanographer in charge of IOC's International Tsunami Information Center, gave UPI an estimate of 700,000 to 750,000 deaths.

Later,[60][61] he said the population density and the 93% destruction rate of residential buildings in downtown Tangshan (where 730,000 people resided)[d] justify an estimate of 655,000 to 779,000 dead.

In August 1976, Taiwan's Military Intelligence Bureau quoted their agents in China had learnt the death toll was over 100,000, with about 900,000 injured.

[62] On 5 January 1977, Taiwan intelligence claimed they obtained a document dated 6 August 1976, nine days after the earthquake, that found 655,237 dead and 79,000 injured.

[63] The alleged document was conference materials prepared by Hebei provincial agencies for the third batch of armed police who were standing by reinforcement orders.

[64] The remarkably low death toll of the Haicheng earthquake the previous year – initially said to be fewer than 300,[65] much later estimated at a still very modest 2,041[66] – had been credited to measures taken in response to an accurate and timely prediction.

This was touted as demonstrating the validity of the Chinese methods of earthquake prediction (including inspiration from "Mao Zedong Thought"[67]) and "the superiority of our country's socialist system!

[81] Tangshan is located particularly over a northeast oriented syncline, a fold in the sedimentary strata that has brought massive deposits of coal close enough to the surface to be mined.

[81] This craton (see figure) was formed approximately two billion years ago[82] by the collision of two major crustal blocks that left a belt of uplifted mountains – the Central (China) Orogenic Belt (COB) – that crosses China approximately southwest to northeast, passing just west and north of Beijing.

It is also the location of over half of the destructive earthquakes in Hebei province,[84] as under the plain several fault zones (oriented parallel to the Central Orogenic Belt) terminate against the Yanshan mountains.

[88] The surprisingly light death toll – initial reports were of "very few people killed",[89] but later determined to be a modest 2,041[66]—for this magnitude Ms 7.5[1] quake, attributed to the precautionary measures taken following a definite short-term prediction, was proclaimed as a demonstration of the superiority of China's socialist system,[90] and incidentally a validation of the Chinese methodologies.

However, it was later determined that the most important factor in anticipating the Haicheng earthquake was the extended series of significant foreshocks ("powerful messages from nature"[91]), and the low casualty rate was due largely to the time of day, hitting in the early evening when most people were neither at work nor asleep.

[94] At the time, the Chinese methods of earthquake prediction mainly consisted of watching for various precursors, including foreshocks,[95] and were celebrated for their success at Haicheng and elsewhere.

[99] The warnings that were made and precautions taken happened largely at the local level, based on general middle-term predictions, enhanced public awareness due to an educational campaign,[100] and a series of foreshocks.

[106] The next morning, at an emergency meeting he requested with the Bureau's leadership, Wang was reportedly told by Deputy Chief Cha Zhiyuan that "We are currently very busy.

These were often based on doubtful theories notorious for false alarms[109] that earthquakes can be predicted on the basis of droughts,[110] daily temperatures,[111] variations in geomagnetism,[103] or isolated anomalous phenomena.

They were often too broad (magnitude "of at least 4.0 in the area of Beijing, Tianjin, Huailai, Tangshan, Bohai, and Zhangjiakou",[103] "in a few years"[112]) to warrant large-scale societal and economic disruption.

Footage of the incident appeared in the film Days of Fury (1979), directed by Fred Warshofsky and hosted by Vincent Price.

[116] The link between politics and earthquake prediction is well expressed by the following statement: 'This is eloquent proof that in socialist New China, under the leadership of Chairman Mao and the Communist Party and by relying on the masses and professional seismological workers armed with Marxism – Leninism – Mao Tze-tung thought and preserving in practice and summing up experience conscientiously, not only can signs indicating an earthquake be observed but predictions and forecasts can be made and damage can be greatly minimized by doing a good job of precautionary work'.See also Cha (1976, p. 7), attributing achievement of rapid progress to "the victory of our great proletarian cultural revolution.