At 21:19:46 on August 8, Beijing time, a magnitude 7.0 earthquake occurred in Jiuzhaigou County (33.20 degrees north latitude, 103.82 degrees east longitude) in the Sichuan Aba Tibetan and Qiang Autonomous Prefecture, with a focal depth of 20 kilometers. There have been many aftershocks since then. Sichuan, Gansu, Qinghai, Ningxia, and Shaanxi provinces felt obvious earthquakes.
If the memory is not bad, in recent years, there have been 142 consecutive earthquakes of magnitude 3 or higher in Shu. The several major earthquakes in Sichuan’s history are shocking.
As a battleground for military strategists in ancient times, why did the Sichuan Basin experience frequent earthquakes? Before answering this question, let’s start with a simple science on the causes of earthquakes.
The interior of the earth can be divided into three layers: crust, mantle, and core. Assuming that the egg is the earth, the eggshell is the crust, the egg white is the mantle, and the yolk is the core. According to statistics, about 92% of earthquakes occur in the crust, and the rest occur in the upper mantle. Earthquakes can be divided into structural earthquakes, volcanic earthquakes, subsidence earthquakes and induced earthquakes according to their genesis. More than 90% of the world’s earthquakes are structural earthquakes-such earthquakes are caused by rock fractures and displacements.
Because the Qinghai-Tibet Plateau, Sichuan, Yunnan and other places are located at the junction of the Asia-Europe plate and the Indian Ocean plate, the Asia-Europe plate is squeezed and uplifted by the Indian Ocean plate, forming mountain ranges such as the Himalayas and Hengduan Mountains. After a certain degree, if the bearing limit of the rock is exceeded, the rock layer will break and an earthquake will occur.
China is the country with the most earthquakes in the mainland. In terms of the distribution of the main seismic zones, western Sichuan is a zone prone to earthquakes. There are many major seismic zones such as the Longmenshan seismic zone, the Panxi seismic zone, the Songpan seismic zone, and the Minjiang fault zone. Therefore, the frequency of strong earthquakes in Sichuan is higher than The national average is not surprising. The epicenter of the magnitude 7.0 earthquake in Jiuzhaigou County occurred near the Minjiang fault zone.
So some people may ask, since there are many earthquakes in Sichuan, what preventive measures are there?
Relevant national departments delineate a key earthquake danger zone every year, which means that within one year, an earthquake of magnitude 6 or higher may occur in western my country (west of Ning, Gansu, Sichuan, and Yunnan), and an earthquake of magnitude 5 or higher may occur in the east. Approved by the Bureau and the Provincial Seismological Bureau, tracking should be strengthened and efforts should be made to make definite areas for effective predictions before earthquakes.
At the beginning of this year, relevant experts once determined that the area where Jiuzhaigou is located was the national 2017 earthquake risk zone. After research, this year the junction of Gansu, Qinghai and Sichuan has been designated as the annual 6.5 earthquake danger zone. The earthquake was about 50 to 60 kilometers away from this danger zone, close to the Sichuan side.
Although I have noticed in the annual forecast, but in the short-term forecast level, no more clues have been found. In general, the 3-month forecast is a short-term forecast.
At present, it is short-term forecasting that can really produce timeliness, but this aspect is still difficult to forecast.
In addition, the implementation of compulsory national standards for the “China Earthquake Motion Parameter Zoning Map” has also effectively improved the seismic resistance of buildings in various places.
There is always nothing wrong with building a strong house!