As the name implies, an over fortification earthquake is an earthquake whose intensity exceeds the local (building) seismic fortification standard.

Taking the big earthquake as an example, the Wenchuan earthquake has a magnitude of 8.0, an epicenter intensity of 11 degrees, and the local fortification is 7 degrees, 11-7=4>0, which means that an earthquake with excessive fortification occurred;

Overfortification does not occur only in the event of a large earthquake (the fortification areas of 6 and 7 degrees in our country account for 82% of the land area). Taking a relatively small earthquake as an example, at 22:55 on June 17, 2019, the Changning earthquake in Yibin, Sichuan, had a magnitude of 6.0, an epicenter intensity of 8 degrees, and the local fortification was 6 degrees, 8-6=2>0, which is also an over fortification earthquake;

At 04:33:31 this morning, the magnitude 6.0 earthquake occurred in Luzhou, Sichuan Province. Because it was a shallow earthquake, the epicenter intensity was estimated to be about 8 degrees. Most of the local fortifications were 6 degrees, and a few were 7 degrees, so it was also an over fortification earthquake.

The zoning of the Seismic Ground Motion Parameter Map in China shows that except Jiaming Town, Yusi Town and Fangdong Town, the other 16 towns in Luzhou County, Sichuan Province are all 6 degree fortified areas.

It is not the earthquake itself that kills or injures people in an earthquake, but the buildings collapsed or furniture overturned due to the earthquake. Because of the "hard to hard" seismic principle, traditional buildings are often hard pressed to cope with super fortification earthquakes (decoration damage, furniture overturning, building cracking and even collapse). The Regulation on the Administration of Earthquake Resistance of Construction Projects, which came into force on September 1, contains such a requirement as "to ensure that the requirements for normal use can be met in the event of a fortification earthquake in the region". What is the "normal use requirement"? In addition to ensuring that the main body of the structure remains intact after the earthquake, normal use requires that non structural members, equipment and pipelines in the building can operate normally after the earthquake to meet the goal of sustainable function of the building after the earthquake. This is the most important significance of building vibration reduction and isolation technology!

Supplementary knowledge:

Magnitude, intensity and seismic fortification intensity (fortification standard) are three different concepts.

Magnitude is a measure of earthquake energy, while seismic intensity refers to the intensity of the ground and various buildings in a certain area being damaged by an earthquake, and is a measure of the impact of an earthquake on a certain location. After the occurrence of the same earthquake, different regions have different degrees of damage and intensities affected by the earthquake. The greater the damage affected by the earthquake, the higher the intensity.

There is only one magnitude value for each earthquake, but the intensity varies depending on the observation location.

Seismic fortification intensity refers to the (national standard) that stipulates an earthquake intensity as the basis for local seismic fortification. In general, the seismic fortification intensity can adopt the basic seismic intensity of the Seismic Parameter Zoning Map of China. The basic seismic fortification objectives of buildings designed according to traditional seismic design are: when they are affected by frequent earthquakes with seismic fortification intensity lower than the local seismic fortification intensity, the main structure can continue to be used without damage or repair; When affected by a fortification earthquake equivalent to the local seismic fortification intensity, damage may occur, but it can still be used after general repair; When it is affected by a rare earthquake that is higher than the seismic fortification intensity of the region, it will not collapse or cause serious damage endangering life. (Note that this is a traditional seismic design)

Earthquake resistance can not be said to resist earthquakes of several magnitudes, but to resist earthquakes of "several magnitudes"!