1976 Tangshan Earthquake: The Most Tragic Page of Modern Chinese History
The 1976 Tangshan Earthquake was one of the biggest earthquakes of the 20th century. And by the number of victims, it ranks first in the world in this century. The disaster in Tangshan China happened on July 27, 1976.
Causes of Tangshan Earthquake
Tangshan is located in northern China, 150 kilometers east of the Chinese capital Beijing. Chinese seismologists have long noticed the potential for major earthquakes in this region. And in fact, this type of tectonic activity in northern China occurs frequently.
Seismic activity in northern China is high. A large number of strong earthquakes have been reported here in past centuries. The fourth period of high seismic activity began in 1815 and continues to this day. Since the 1966 earthquake in Xingtai (425 km southwest of Tangshan). There have been frequent seismic events with a magnitude greater than 6.0.
Since 1972, anomalies have been regularly observed in northern China, which are precursors to earthquakes. In the Yan Shan fault zone area, a decrease in the frequency of small earthquakes, uniform distribution of “first motion” during small earthquakes. The formation of seismic faults, rupture, and a reduction in the ratio of P- and S-wave velocities were observed.
Based on a combined analysis of tectonic conditions, seismicity, and the presence of precursors. It was predicted in June 1974 that an earthquake of magnitude 5 to 6 would occur in the next year or two in the Beijing-Tianjin area and north of Bohai Bay.
New assumptions were made in January 1976 by employees of the state seismic bureau: “earthquakes of magnitude 5-6 might happen in the area Beijing-Tianjin-Tangshan and in the area Bohai-Zhangjiakou (310 km north-west of Tangshan). Special attention was supposed to be paid to Tangshan and Chaoyang and between Beijing and Tianjin.
Since the Haicheng earthquake in February 1975, many weak and moderate earthquakes have occurred frequently in northern China in Shandong, Hebei, Taiyuan, Shanxi, and Inner Mongolia. However, a stronger earthquake was not predicted.
A few days before the earthquake, sharp fluctuations in groundwater levels and abnormal animal behavior were noted in Tangshan. But they did not convince anyone that a stronger earthquake could occur.
Effects and Intensity After Earthquake
The zone of maximum destruction of the 1976 China Earthquakes is elliptical in shape. About 47 square kilometers and includes the city of Tangshan and the area along the Beijing-Shanhaiguan railroad. The intensity in this area is described as XI.
In this area, all buildings lay in ruins, and only a few were severely damaged, rails were bent, and all road bridges were broken. The area where the earthquake intensity was X was also elliptical and stretched northeastward. Its area was approximately 370 square kilometers.
In this area, about 80% of all houses and almost half of the industrial buildings were destroyed. Fountains of water and mud poured out of the ground. Nearly all irrigation wells ceased to function.
The intensity IX region was rhombus-shaped and about 1800 square kilometers in area and also northeast direction. Most residences were damaged, and 40% of them collapsed. Half of the industrial structures were destroyed.
The region of intensity VIII spread in a southeasterly direction and had an area of about 7,300 square kilometers. In this region, most of the buildings were very old and not earthquake-resistant, and therefore the damage was severe.
The region of intensity VII had an area of about 33,000 square kilometers. The damage here was less, some very old houses collapsed, and most buildings suffered varying degrees of damage.
And in the southern region, the sediment layer is thick, it consists mainly of sand or clay, and the water table is high. Therefore, the damage in that area was very severe, especially to old and poorly built structures.
Casualties and Damages of China 1976 Earthquake
The earthquake received the nickname “Great Tangshan Earthquake”. It nearly flattened the industrial city of Tangshan to the ground. The authorities of China officially informed about 242 thousand victims. But according to unconfirmed information, the number of victims can reach 655 thousand.
Moreover, more than 700 thousand people were wounded and the area of the damaged buildings even reached Beijing. Most people died because of the collapse of non reinforced blockhouses, and as the earthquake happened in the deep night. Almost all people were at home and slept. The epicenter of China 1976 earthquake was in the Tangshan. And the earthquake’s origin was only 9 kilometers from the earth’s surface. On the same day, another strong earthquake with magnitude 7.1 occurred 43 kilometers to the southeast.