Is Changchun an earthquake zone? Is the probability of an earthquake high? Has there been an earthquake in Changchun in history?

Statistics of a large number of historical earthquakes and present earthquakes show that seismic activity has a certain periodicity in time, that is, earthquakes occur with high frequency and intensity in a period of time, which is called seismic active period; While the frequency and intensity of earthquakes in another period are relatively low, which is called the quiet period of earthquakes. According to the characteristics of earthquakes, several "active scenes" can be drawn during the active period. Since this century, China has experienced four periods of seismic activity, and the fourth period is roughly 1966- 1976. During the period of 10, there were 14 major earthquakes with magnitude above 7 in Chinese mainland, which caused 270,000 deaths and tens of billions of economic losses. According to the research of most experts, the 1990s to the beginning of the next century may be the fifth climax of earthquake activity in Chinese mainland, during which several earthquakes of magnitude 7 or even greater may occur. The main active area of strong earthquakes will be in the west of China, and moderate and strong earthquakes will be relatively active in the east.

(B) the characteristics of earthquake disasters

1, suddenly

Earthquakes are generally natural phenomena that suddenly occur in a calm situation. A strong earthquake can cause great damage in a few seconds or tens of seconds, and it can turn a city into ruins in an instant. Especially the earthquake at night, the consequences are more serious. For example, the Tangshan earthquake occurred at 3: 42 in the morning, when people were asleep and didn't be alert in advance, causing heavy casualties and economic losses of/kloc-0.00 billion yuan.

2. verticality

In an area, or after a strong earthquake, in order to adjust the regional stress field, or the continuation of rock fracture, seismic activity often occurs vertically in a certain period of time, causing disasters continuously.

3. Continuity

Strong earthquakes can not only directly cause damage to buildings and engineering facilities and casualties, but also often lead to a series of secondary disasters and derivative disasters, causing greater damage. Such as fire, flood, toxic gas and chemical leakage, bacterial pollution and radioactive pollution caused by earthquake disasters, as well as secondary disasters such as landslides, mudslides and tsunamis. And all kinds of social losses caused by the above disasters. 1 September, 9231Japan's Great Kanto Earthquake triggered a fire, which triggered 136 fires, burned 45 houses, and 56,000 people were burned to death, most of whom died of suffocation.

(3) Spatial distribution characteristics of earthquakes

The geographical distribution of earthquakes is influenced by geological structures, so there are certain laws, the most obvious of which is zonality. Earthquakes around the world are mainly distributed in: First, the Pacific Rim seismic belt, which is the most active seismic belt in the world, and 80% of the global earthquakes and 75% of the released seismic energy are concentrated in this area. The second is the Eurasian seismic belt, where about 15% of the world's earthquakes occur.

China, located in the southeast of Eurasia plate, is an earthquake-prone country influenced by the Pacific Rim seismic belt and Eurasian seismic belt. According to statistics, earthquakes of magnitude 7 or above in Chinese mainland account for 1/3 of the global earthquakes of magnitude 7 or above, and the number of earthquake deaths accounts for 1/2 of the global total. There are 4 1% of the country, more than half of the cities are located in areas with basic earthquake intensity above 7 degrees, and areas above 6 degrees account for 79% of the country.

(d) Hypothesis of the cause of the earthquake

Why are global earthquakes concentrated in the above two seismic zones? What is its genetic mechanism? This is an important theoretical problem in seismology. At present, there are several hypotheses: continental drift theory, submarine expansion theory and so on. At present, the more popular and accepted theory is plate tectonics. 1965, the famous Canadian geophysicist Wilson first put forward the concept of "plate". 1968, the French divided the global lithosphere into six plates, namely Eurasia, Pacific Ocean, America, Indian Ocean, Africa and Antarctica. The boundary between plates is an area where the crust is relatively active and volcanoes and earthquakes are relatively concentrated. Plate theory is the synthesis and extension of continental drift and submarine expansion. Although it can't solve all the problems of the earth's motion, it puts forward the direction and opens up new ideas for the theoretical study of the causes of earthquakes.

...