Classification of earthquakes according to their intensity
In the times when earthquakes were not observed by instruments (instrumental) methods, in order to compare different earthquakes with each other according to their intensity, their manifestations on the earth's surface (destruction, damage, etc.) were used as a basis.
In fact, there was a great deal of subjectivity and uncertainty in this comparison based on human perception.
For example, people considered an earthquake that seriously damaged their house to be stronger than an earthquake that was felt lightly. However, a stronger earthquake could be felt faintly simply because it was far away.
Despite all this, since the middle of the 19th century, attempts were made to classify earthquakes according to human perception, damage to physical objects, and visual impact on the surrounding geological environment. At the end of that century, the Rossi-Forel (RF) earthquake intensity scale developed in Switzerland and Italy was widely used. In this table, seismic vibrations are divided into ten degrees according to their intensity.
In 1902, a new 12-point intensity scale was developed by Giuseppe Mercalli in Italy.
In 1931, American scientists G.Wood and F.Newman, and in 1956, Ch.Richter made certain changes to that scale, and now this scale is called "Modified Mercalli scale (MMI)".
Since 1964, the 12-point MSK-64 scale has been officially adopted in Eastern Europe, including the former USSR, which included Azerbaijan. The name of the scale consists of the initials of the surnames of the seismologists who compiled it: S.Medvedev (USSR), V.Sponheuer (GDR) and V.Karnik (Czechoslovakia). In addition to the slightly different MMI and MSK-64 scales, there is a 12-point European macroseismic scale (EMS, 1998), as well as a 7-point scale of the Japan Meteorological Agency (JMA), which has been applied in Japan since 1951.
The MSK-64 seismic intensity scale is detailed below.
I point. The earthquake is not felt.
II points. It is hardly felt. Vibrations are felt only by people in the house, especially on the upper floors.
III points. Weak vibrations. The earthquake is felt by a few people who are at home and by a few people outside. It is similar to the vibrations produced by a passing car. Attentive people notice that light objects sway weakly and strongly on upper floors.
IV points. Obvious vibration. The earthquake is felt by most of the people inside the building and by some outside. Some of the sleepers wake up, but they are not afraid. It is similar to the vibrations produced by a heavy machine. Windows and doors rattle, floors and walls creak. Vibration of furniture, light swaying of hanging objects, ripples of liquids in open containers are observed. Impulse is felt in stationary cars.
V points. The earthquake is felt by everyone inside the building, and by many outside. Most of the sleepers wake up. Some people run outside. Animals are worried. The whole building is shaking. Hanging objects swing violently. Some unstable objects tip over or slide. Doors and windows open and slam again. Liquid spills from open full containers. It is similar to the vibrations produced by a heavy object falling inside the house. In rural houses built of mud bricks and clay, light damage, small cracks in the plaster may appear, and the plaster may fall off. In some cases, the discharge of springs changes.
VI points. The earthquake is felt by many people inside and outside the building; many of them run out into the street in fear. Some lose their balance, pets run from their nests. Breaking of glass containers, falling of books, movement of heavy furniture can be observed.
Some of the block and panel type, ordinary brick buildings and most of the mud brick and clay houses have slight damage and small cracks. In rural houses built of mud bricks and clay, sometimes there are secondary damages, cracks appear in the plaster on the walls, the plaster breaks off in large parts, etc.
VII points. Buildings are damaged. The vast majority of people run to the street in fear. Most of them can hardly stand on their feet. Drivers feel the earthquake while driving.
Most of the reinforced-concrete carcass buildings have light damage, small cracks are formed in the plaster, parts of the plaster are broken off, secondary damage is observed in ordinary brick houses, large-block and panel buildings, and small cracks are observed in the walls. Large damage and deep cracks in the walls are noted in the mud brick village houses. In some of these houses, the walls of the house are broken, there are direct cracks in the walls, and the collapse of connections between separate parts of the building, etc. can be. In some cases, landslides on sharp roadside slopes, cracks in the roads are noted. A wave forms on the water surface, the water becomes cloudy due to rising silt, the water level in wells changes, and in some cases, existing springs disappear or new ones are formed.
VIII points. Buildings are seriously damaged. Fear and panic sets in. Drivers are also worried. Tree branches are broken, heavy furniture slides and sometimes falls, some hanging lamps are damaged. Reinforced-concrete carcass buildings have secondary damage, small cracks in the walls, and some severe damage, deep cracks in the walls. Heavy damage, large cracks in the walls, collapse of the walls, and the formation of direct cracks are observed in the block and panel buildings. In village houses built of mud bricks, walls collapse, direct cracks appear, and sometimes the houses collapse completely. Breaking of pipelines, sliding of statues, overturning of tombstones, collapse of stone fences are noted.
Cracks several centimeters in size are formed in the soil, water is lost in some wells or water is filled in dry wells.
IX points. Damage to all buildings, general panic, screaming and running of animals are observed.
Deep cracks in the walls of reinforced concrete carcass buildings, wall collapse, direct cracks and even complete collapse occur in some of them. In ordinary brick, block and panel buildings, direct cracks in the walls, collapse of some walls, and sometimes complete collapse are observed.
Monuments and columns topple over, underground pipelines are broken, and in some cases, railway flights are bent.
The width of the cracks in the soil reaches 10 cm; there are cases of landslides, large waves on the water.
X points. Damage is noted in all buildings.
There are direct cracks in the walls of reinforced concrete carcass buildings, collapse, and sometimes complete collapse of the building, ordinary brick, block and panel buildings, as well as complete collapse of mud brick village houses.
There are dozens of centimeters, sometimes up to 1 m wide cracks in the soil, landslides on sharp slopes, mixing of silt and sand masses in coastal regions, overflow of water from rivers and lakes, formation of new lakes.
XI points. Disaster strikes. Well-constructed buildings, bridges, dams, railroads are seriously damaged, underground pipelines collapse, and highways become unusable.
Wide cracks, displacements in horizontal and vertical directions, mountain avalanches occur on the earth's surface.
Special research is required to determine the intensity of the earthquake.
XII points. It can be said that damage to all above-ground and underground structures, changes in the surface of the earth, large cracks accompanied by large displacements in the soil, mountain avalanches are observed, lakes, waterfalls are formed, and rivers change their direction.
Special research is required to determine the intensity of the earthquake.