Original: Duan Hongbin source: official account: Lao Duan’s viewpoint
Since July this year, many parts of the country have suffered from the worst drought in a hundred years. The Jialing River, the main tributary of the upper reaches of the Yangtze River, has bottomed out. From Sichuan to Anhui, from Poyang Lake to Taihu Lake, the entire middle and lower reaches of the Yangtze River have suffered serious drought. The Yangtze River Basin, which should have been in the flood season, has stopped raining.
Although I don’t want to be alarmist, there is one risk I have to mention, that is, the theory of “drought earthquake relationship”. Not many people know this theory, but I think it is very important, so let me introduce it first.
The person who proposed the theory of “relationship between drought and earthquake” is Geng Qingguo. He is a geologist of the State Seismological Bureau. When he studied the relationship between earthquakes and meteorology, he found that the epicenter area of a large earthquake with magnitude 6 or above was often a dry area within one to three years before the earthquake. The larger the area of the dry area, the larger the magnitude. If the earthquake occurred in the third year after the drought, the magnitude would be larger than that in the first year.
He gave his own explanation for why there was an earthquake after the drought:
The direct cause of an earthquake is the concentrated release of stress in the crust. Although the speed of stress release is very short, the incubation time is very long. In the process of earthquake preparation, there are not only mechanical processes, but also various physical and chemical reactions such as heat, electricity and magnetism. In this process, a large amount of energy released will cause abnormal changes in the low-level atmosphere.
During the preparation of a large earthquake, due to the increase of geothermal energy, the ground appears dry and hot characteristics, which will lead to a great reduction of water vapor content in the air and a small humidity, which will make it difficult to form clouds. The lack of clouds allows the sun to shine directly on the ground, which exacerbates the drought.
According to his theory, it was not drought that caused the earthquake, but the special geological changes in the earthquake area 1-3 years before the occurrence of the great earthquake made the ground temperature rise, thus forming a special high-pressure belt, which changed the local climate environment and made it difficult for precipitation to occur, so there was drought.
Now that we have the theory, let’s see if we can integrate it with practice. The following table shows that from the year 231 BC (the 16th year of the first emperor of Qin Dynasty) to the year 1971 ad, there were 69 earthquakes of magnitude 6 or above in North China and the Bohai Sea in the past two thousand years, of which only two did not have drought before the earthquakes, and the remaining 67 were drought before the earthquakes.
Geng Qingguo also found that from 1956 to 1971, there were 46 dry areas in China, of which 39 dry areas had earthquakes of magnitude 6 or above within 1-3 years after the disaster. The probability of major earthquakes after the drought was as high as 84.8%, and only 15.2% of the dry areas had no major earthquakes within 3 years after the disaster.
The author also pointed out that the drought in the relationship between drought and earthquake is not the same as that in agriculture. The lack of precipitation during the growing period of crops in agriculture leads to a reduction in grain production, which is called drought. However, drought in the relationship between drought and earthquake refers to severe drought, which lasts for a long time and covers a wide area. The area where the precipitation exceeds the lowest value over the years is a clear signal to determine the earthquake risk area.
The author also gives several recent examples. For example:
In 1972, North China suffered a severe drought that was not seen in decades. As a result, a 7.3 earthquake occurred in Haicheng, Liaoning Province in 1975, and a 7.8 earthquake occurred in Tangshan in 1976.
In 1972, a serious drought occurred in Southwest China. In 1973, an earthquake of magnitude 7.9 occurred in Luhuo, Sichuan Province. In 1974, an earthquake of magnitude 7.1 occurred in Zhaotong, Yunnan Province.
3. If the above examples are not significant enough, there was a severe drought in Sichuan from 2006 to 2007, and then the Wenchuan earthquake in 2008.
In 2006, Sichuan and Chongqing in China suffered a severe drought, and some areas suffered a severe drought once in a century. The temperature in some areas exceeded 40 degrees for many times, and even reached 44 degrees. What is more terrible is that the drought lasted until 2007. On May 12, 2008, a magnitude 8 earthquake occurred in Wenchuan.
In fact, the ancients had long discovered the “relationship between drought and earthquake”, but it did not rise to theory. There is a saying in Mandarin:
In the second year of Youwang, all three rivers in the Western Zhou Dynasty were shocked. Uncle Boyang said: “… When the river runs out, the mountain will collapse……”.
Uncle Boyang said that when the river dried up, the mountain would surely collapse. At that time, the Jingshui, Weishui and Luoshui were all dry, so the Qishan earthquake occurred. The Qishan earthquake in the second year of Zhou Youwang was the first earthquake with a magnitude of 6 or above recorded in Chinese history.
The above basically gives a brief overview of the “drought and earthquake theory”. I certainly do not know whether there will be a large earthquake in the next 1-3 years after a large-scale drought in China, but I think this possibility cannot be ruled out.