2020-07-12

Why did the earthquake still happen in Tangshan

By yqqlm yqqlm

First understand a geological term-kraton.

Simply put, craton refers to the ancient and stable part of the continental crust, which is rarely affected by orogeny. It includes a portion of the top of the earth’s outermost crust and mantle, with a total thickness of about 150 kilometers to 200 kilometers. As a whole, it”floats” above the underlying asthenosphere. Cratonization is an important event in the formation of a stable continent, and there is no repetition in the history of earth evolution.

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Chinese The North China Craton is extremely special, with diverse rock types and complex structural evolution, which are rare in the world. Since entering the Cenozoic (65 million years), the eastern part of the North China Craton has been severely damaged. Today, the thickness is only 60 kilometers to 80 kilometers, and the thickness of more than 100 kilometers is unknown.

​According to the observations made by domestic scientists on the North China Craton, due to the vertical unevenness in the continental lithosphere, there is a weak mechanical layer in the craton lithosphere with relatively high mechanical strength. Under the influence of the Mesozoic Pacific plate subduction, the existence of this weak layer caused the bottom of the lithosphere in the eastern North China Craton to undergo a bottom-up transformation. Eventually it caused geological instability in North China.

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Subduction of the Pacific Plate

At the same time, Yanshan block uplift and subsidence movement of the North China Plain block form local tension, which is also One ​​of the reasons for the formation of the North China Plain earthquake zone. North China Plain Seismic Belt:The southern boundary is roughly located on the Xinxiang-Bengbu line, the northern boundary is located on the south side of Yanshan, the western boundary is located on the east side of Taihang Mountain, and the eastern boundary is located on the western edge of the Lower Liaohe-Liaodong Bay depression, extending southward to southeast Tianjin. The eastern part of Jinan reaches Suzhou area.

The Tangshan earthquake area is located in the north-east direction of Tangshan-Hejian—Cixian newborn fault zone and the northwest direction The intersection of Zhangjiakou-Penglai fault zone. The special regional structural location of the Tangshan earthquake area is the main cause of the occurrence of Tangshan earthquakes.

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North China Seismic Belt

Since the 20th century, there have been nearly 800 earthquakes of magnitude 6 and above in China, covering all provinces, autonomous regions, and municipalities except Guizhou, Zhejiang and the Hong Kong Special Administrative Region. 53%of earthquake deaths. The Chinese often take pride in &34; we use 7%of the world’s land to feed 22%of the world’s population &34; but few people know that China’s 7%of the country’s land has also suffered 33%of the global continent earthquake .