There is a strict difference between earthquake intensity and earthquake magnitude and should not be confused. Earthquake magnitude represents the magnitude of the earthquake itself, corresponding to the seismic wave energy emitted by the source, and the same earthquake should have only one earthquake magnitude value. But the damage caused by the same earthquake in different places is different. In order to measure the degree of earthquake damage, scientists "made" another "ruler"-earthquake intensity. The seismic intensity of a place after an earthquake is related to magnitude, focal depth, epicentral distance and soil conditions in the earthquake area. This is the same reason that the degree of damage from far and near is different after the bomb explodes. The amount of explosives in the bomb is like magnitude; Bombs destroy different places as much as they do.

Earthquakes are large and small, far and near, and the damage caused by earthquakes with different sizes and epicentral distances is different, so the methods of taking risks will be different. Don't worry about distant earthquakes and small earthquakes. Only near earthquakes and large earthquakes need to be avoided. Therefore, when an earthquake occurs, we should be calm and pay attention to judging the size and distance of the earthquake. The difference between teleseism and near earthquakes is that teleseism has no ups and downs, but only slow horizontal shaking; The recent earthquake was first bumpy, and then began to shake horizontally. The difference between a big earthquake and a small earthquake is that the nearby small earthquakes don't feel obvious ups and downs and horizontal shaking, but only feel slight shaking, and some only feel pushed.

However, large earthquakes are very strong and rapid in ups and downs and horizontal shaking; The greater the magnitude, the greater the amplitude, and the longer it takes to bump up and down and shake horizontally. When the house is violently jolted and shaken, people can feel that the house is violently shaking and crumbling, and the items placed fall down, and the people who are moving will fall down, and those who are in an unstable state will fall away from their original places and have a sense of vomiting. When a big earthquake happens, sometimes there will be some unimaginable phenomena, such as strong ground sound, strange ground light, unpleasant ground gas and so on. According to the investigation of the Wenchuan earthquake in 2008, when the earthquake happened, people on high-rise buildings in Beijing, Shanghai and other places far away from the epicenter felt dizzy like waves.

In the epicenter and nearby areas, people first felt a violent jump up and down, followed by a large swing from side to side. The time difference between violent jumping up and down and large swinging from side to side varies from two or three seconds near the epicenter to more than ten seconds in the distance. It lasts about two to three minutes from the violent and large swing at the beginning to the obvious weakening. According to the survey, most houses collapsed between 14: 28 and 14: 30 when the earthquake occurred.

The epicenter measured according to seismograph records is called microcosmic epicenter, which is expressed by latitude and longitude. According to the macroscopic survey of earthquakes, the epicenter is called the macroscopic epicenter, which is the geometric center of the extreme earthquake zone (the most damaged area near the epicenter) and also expressed by latitude and longitude. Because of different methods, macro-epicenter and micro-epicenter often do not coincide. Before 1900, when there was no instrument record, the epicenter location of the earthquake was always the macro epicenter determined according to the damage range.