Taiwan twice in a row!Let's take a look at the "old nest" of the earthquake

Text ｜ Li Zefeng (Special researcher at the School of Earth and Space Science, University of Science and Technology of China)

Earthquake is one of the natural disasters facing human society. In the history of many countries, the earthquake has left painful memories, including the Tangshan earthquake in China in my country in 1976 and the 2008 Wenchuan Earthquake, Japan's 2011 Northeast Earthquake and the United States in the San Francisco Earthquake in 1906.

On September 17th and 18th, there were two destructive earthquakes occurred in Taiwan Province in Taiwan. Taiwan is located on the border between the Philippines and the Eurasian sector. In 1999, a magnitude 7.5 earthquake occurred in 1999, causing over 200,000 people to die and more than 10,000 injuries.

So, what are the laws of earthquakes? Can the earthquake be predicted? In fact, this is not only a matter of concern to the public, but also a problem that earthquakers have always thought about it. Unfortunately, the current earthquake prediction is still a global scientific problem. However, this does not mean that we know nothing about the earthquake. For example, we already have a certain understanding of the "old nest" break zone of the earthquake.

What is a broken zone

Natural earthquake occurred on a break zone. The broken belt can be said to be the home of the earthquake. How did the broken belt come from?

We know that the outermost layer of the earth is a rock ring, but the rock rings are not integrated, but the seven major sectors are "broken into", and the boundary between the sectors is a large fracture zone. Driven by the gravity effects of the mantle and the sector itself, each plate has been in relative movement. Since there is a relative movement, the boundary of the plate is inevitable. One of the results is the earthquake. This is the greatest achievement in the field of earth science in the 20th century -the basic understanding of the theory of sector structure.

In short, the broken belt can be seen as a large crack in the rock ring.

There is a broken belt on the boundary of the plate. Is there any interior of the plate? some. Similar to the concept of the sector, earth scientists have found a more subdivided block inside the plate, called the plot. On the boundary of the plot, various types of fracture bands have also been formed.

Compared with the fracture zone of the sector boundary, the scale and relative sliding rate of the internal fracture band of the plate are smaller. However, this does not mean that the seismic level or less harmfulness inside the sector is less. Long -term stress accumulation (hundreds of years or even thousands of years) can cause large earthquakes of level 7 or even level 8 or even above the sector.

my country's broken zone

To understand the distribution of earthquake disasters, we must clear the distribution of the broken belt.

In the eastern region of my country, the most obvious is the Lugu Fractoring Belt (called Yilan -Itong Fracture Belt in the north), which is the most important source of earthquake threats in the eastern region. Internationally recognized that the 1975 Haicheng earthquake, which was successfully predicted, occurred on the Fracture Belt of the Lugu.

In North China, there is a break belt with a break belt with the Lugu. It is called the Zhangjiakou -Bohai Sea Fracture. It is the culprit of the Tangshan earthquake in 1976.

Taiwan provinces in the southeast of my country are on the Philippine sector to the Eurasian sector's dive border. It has a very complicated and active fault system, mixed with different depth of anti -rushing faults and slipping faults. In 1999, the collection of earthquakes occurred on the anti -cage fracture layer.

In the western region of my country, there are many broken belts, dazzling, most of them exist inside and surrounding the Qinghai -Tibet Plateau. The Alkin Fracture and Haiyuan Fracture in the north (a large earthquake in Haiyuan in 1920) to the small rivers of the small river in the south and the Red River breaks, which brought serious earthquake disasters to Tibet and Qinghai and surrounding Sichuan, Yunnan, Gansu, Xinjiang and other places. Essence

Why is the earthquake activities in the Qinghai -Tibet Plateau and the surrounding surroundings so severe? The main driving force is the squeezing of the Eurasian sector in the Indian Ocean sector. On the one hand, it has caused a bulge of the Qinghai -Tibet Plateau. On the one hand, it puts tremendous pressure on the interior and surrounding plots of the Qinghai -Tibet Plateau. When the friction on the fault cannot bear the pressure, it will be murdered, causing the earthquake.

Recent seismic break zone

Since 2021, a magnitude 6 or above earthquake occurred in my country.

Among them, in 2021, the MW6.1 earthquake in Yunnan Yang (Visse -Qiao Hou Breck), Qinghai Mado MW7.3 Earthquake (Kunlun Mountain Estuary -Jiangwu break), Gate source MW6.7 earthquake (cold dragon ridge break); 2022; 2022 In the Lushan MW5.8 earthquake (Longmen Mountain Fragment) and Luding MW6.6 earthquake (Fresh Water River Fragment) in Sichuan, these earthquakes occurred on the different fracture bands inside and surrounding the Qinghai -Tibet Plateau.

Inside alone, there are three main fracture bands with Y -shaped, that is, the Longmen Mountain Fragment of the Longmen Mountain in the northwest of the Sichuan Basin, the break from the interior of the Qinghai -Tibet Plateau to the southeast, and the Anning River fault to the south.

On the broken Longmen Mountain Fracture, the 2008 Wenchuan Earthquake and the 2013 Lushan Earthquake occurred, while the nearest Luding earthquake occurred at the southernmost tip of the freshwater river (Musi).

Two earthquakes above 6 or more occurred in Taitung County and Hualien County, Taitung County, Taiwan Province on September 17, may be related to the central mountain fault system on the island of Taiwan.

The survey, nature portrayal, and risk assessment of the broken belt have always been the top priority of earthquake disaster research. Earth scientists comprehensive seismics, geological, geological surveying, and earth dynamics have conducted long -term multi -angle and multi -scale research on the broken zone. Essence On the way to find out the "old nest" of the earthquake, earth scientists are conducting unremitting exploration! "China Science News" (2022-09-19 The first edition of the original title "Fracture Belt:" Old Nest "of the Earthquake")

Edit | Zhao Lu

Capture | Zhihai

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