Explanation of key terms related to earthquakes

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2024-04-17

　　The three concepts of magnitude, intensity, and seismic fortification intensity (fortification standards) are easily confused by many people.

　　The Richter Scale is a magnitude scale proposed by two seismologists, Charles Francis Richter and Beno Gutenberg, from the California Institute of Technology in 1935. It is currently the internationally recognized standard for earthquake magnitude.

　　Earthquakes can be classified into the following categories based on their magnitude:

　　The weak earthquake magnitude is less than 3.

　　The magnitude of the earthquake is equal to or greater than 3 and less than or equal to 4.5.

　　Moderate to strong earthquakes with magnitudes greater than 4.5 and less than 6 (such as the Yiliang earthquake).

　　Strong earthquakes with a magnitude equal to or greater than 6 (such as the Yushu earthquake).

　　Among them, earthquakes with a magnitude greater than or equal to 8 are also known as giant earthquakes (such as the Wenchuan earthquake).

　　Earthquake magnitude and earthquake intensity are different concepts.

　　Earthquake intensity refers to the intensity of damage caused to the ground and various buildings in a certain area by an earthquake, and is a measure of the impact of an earthquake on a certain location. After the same earthquake occurs, the degree of damage and intensity affected by the earthquake vary in different regions. The greater the damage caused by the earthquake, the higher the intensity. The determination of intensity is based on human perception, the vibration of furniture and objects, the degree of damage to houses and buildings, and the occurrence of ground damage. The magnitude of intensity is influenced by the following factors: earthquake level, focal depth, epicenter distance, soil and geological conditions, building performance, focal mechanism, topography, and groundwater. For example, under the same conditions, the higher the magnitude, the greater the intensity. The seismic intensity (Mercalli Intensity) is a scale that indicates the degree of earthquake damage and is related to various conditions in the earthquake area, rather than the absolute strength of the earthquake. The earthquake intensity was proposed by Italian volcanologist Giuseppe Mercalli in 1902. and is divided into 1-12 degrees from imperceptible to completely destroyed. More than 5 degrees will cause damage.

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

　　To achieve seismic resistance, it is necessary to conduct seismic design and take seismic measures for buildings during engineering construction.

　　The seismic fortification intensity (fortification standard) refers to a seismic intensity designated by the state as the basis for local seismic fortification. In general, the seismic fortification intensity can be based on the seismic basic intensity of the China Seismic Parameter Zoning Map.

　　The most easily misunderstood aspect is using the magnitude of an earthquake to measure a building's seismic resistance - so the correct way to describe a building's seismic resistance is usually to use earthquake intensity, which is described as the degree of earthquake that the building can withstand, rather than the degree of earthquake it can withstand; The seismic fortification standard for a certain city street should be expressed in terms of seismic fortification intensity, described as XX city, XX district/county, XX street/township as an X-degree fortification area.

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