4hw.org: Recently, there was a 7.0-magnitude earthquake in Jiuzhaigou, Sichuan Province, which attracted national attention. After the Wenchuan earthquake in 2008, the Chinese people "talk about earthquake color change". Every earthquake will cause strong attention. Many people are not familiar with how to divide the earthquake magnitude. Let's have a look at it together!
Magnitude refers to the magnitude of an earthquake. It is a measure of the strength of an earthquake. It is determined by the amount of energy released by each seismic activity measured by a seismograph. The most commonly used magnitude is the Richter magnitude and the moment magnitude. The magnitude is usually expressed by the letter M. the magnitude standard currently used in China is the international general Richter scale, which is divided into nine grades. Generally, an earthquake with a magnitude less than 2.5 is called a small earthquake, 2.5-4.7 A magnitude-6 earthquake is called a sensed earthquake, and an earthquake with a magnitude greater than 4.7 is called a destructive earthquake. For every magnitude difference of 1.0, the energy difference is about 30 times; for every magnitude difference of 2.0, the energy difference is about 900 times. For example, the energy released by a magnitude-6 earthquake is equivalent to that of the atomic bomb dropped by the United States in Hiroshima, Japan. A magnitude-7 earthquake is equivalent to 32 magnitude-6 earthquakes, or 1000 magnitude-5 earthquakes.
Chinese seismic intensity scale
1 degree; no sense - only the instrument can record;
2 degrees; slightly sensitive - a particularly sensitive person feels in complete stillness;
3 degrees; little feeling - a few people in the room have a sense of stillness, and the suspension slightly swings;
4 degrees; more sense - most people in the room, a few people outside have sense, hanging objects swing, unstable utensils make noise;
5 degrees; wake up - most people feel restless outside, livestock, doors and windows make noise, cracks appear on the wall surface
6 degrees; panic - people stand unstable, livestock escape, utensils fall, simple shed damage, steep slope landslide;
7 degrees; house damage - slight damage to the house, damage to the archway and chimney, cracks on the surface and water gushing from sand;
8 degrees; building damage - most buildings are damaged, a few damage subgrade collapse, underground pipeline rupture;
9 degrees; general damage of buildings - most of the buildings are damaged, a few are toppled, archways, chimneys and other collapses, and the rails are bent;
10 degrees; buildings are generally destroyed - houses are dumped, roads are destroyed, mountains and rocks collapse in large quantities, and the water surface waves rush to the bank;
Destruction - a large number of houses collapse, a large section of subgrade and embankment collapse, the surface changes greatly;
12 degrees; mountains and rivers are easy to see - all buildings are generally destroyed, and animals and plants are destroyed due to dramatic changes in terrain;
According to magnitude, earthquakes can be divided into the following categories:
The magnitude of weak earthquake is less than 3. The magnitude of induced earthquake is equal to or greater than 3, less than or equal to 4.5
The magnitude of a moderate strong earthquake is greater than 4.5 and less than 6. The magnitude of a strong earthquake is equal to or greater than 6. Among them, a magnitude greater than or equal to 8 is also called a huge earthquake
Earthquake intensity
The damage caused by an earthquake of the same size is not necessarily the same; the damage caused by the same earthquake in different places is not the same. In order to measure the extent of the damage caused by an earthquake, scientists have made another ruler - earthquake intensity. On the Chinese earthquake intensity scale, people's feelings, the degree of damage caused by ordinary houses and other phenomena are described, which can be used as the basic basis for determining the intensity The factors of seismic intensity include magnitude, focal depth, distance from focal point, ground condition and stratigraphic structure
Generally speaking, the larger the magnitude is, the shallower the source is and the stronger the intensity is. Generally speaking, after an earthquake occurs, the damage in the epicenter area is the heaviest and the intensity is the highest. This intensity is called the epicenter intensity. As the epicenter extends to all sides, the seismic intensity gradually decreases. Therefore, an earthquake has only one magnitude, but the damage caused by it is not the same in different areas The same. That is to say, an earthquake can be divided into several areas with different intensities. This is the same as the destruction degree of a bomb in the near and far places after it explodes. The explosive quantity of a bomb is like magnitude; the destruction degree of a bomb to different places is like intensity
For example, on February 10, 1990, there was an earthquake of magnitude 5.1 in Changshu Taicang. Some people said that it was magnitude 4 in Suzhou and magnitude 3 in Wuxi, which is wrong. No matter where it is, it can only be said that there was an earthquake of magnitude 5.1 in Changshu Taicang, but the intensity of the earthquake in Shaxi Town of Taicang was magnitude 6, in Suzhou it was magnitude 4, and in Wuxi it was magnitude 3. At present, the biggest earthquake recorded by human beings is may 1960 A magnitude 9.5 earthquake struck Chile on the 22nd
There are several different intensity scales used in the world. In western countries, the modified Mercalli intensity scale, or M.M. intensity scale for short, is commonly used. There are 12 intensity grades from 1 to 12. Japan sets the non sensitivity as 0, and the sensitivity as I to VII, with a total of 8 grades. The former Soviet Union and China all classify the intensity scales according to 12 intensity grades. In 1980, China revised the seismic intensity scale (see table)