An earthquake is a sudden release of energy accumulated in elastically deformed layers of rocks.It is the vibrations of the earth’s surface and caused by displacement of rocks along the fault that occurs near the earth’s surface.About one million earthquakes occur on Earth annually, but most of them are so insignificant that they go unnoticed. Really strong earthquakes, capable of causing extensive destruction, occur about once every two weeks. Fortunately, most of them are at the bottom of the oceans and therefore are not accompanied by catastrophic consequences.
The accumulated stresses of the earth’s crust or upper mantle at some point begin to exceed the strength of the mountain nicks in this place, and therefore tectonic deformations occur. The discharge of these stresses causes seismic oscillations in the form of waves, which, upon reaching the earth’s surface, produce destruction.
The area of occurrence of the earthquake – the center ( hypocenter ) of an earthquake is a certain amount of rocks within which inelastic deformations take place and rocks are destroyed. The concept of the focus, or hypocenter, is not strict, but it is important to emphasize that this is not a point, but some space, volume, shape and size of which can be very different.
The epicenter is a projection of the hypocenter on the earth’s surface. The depth of the hypocenter can reach 30 km, and in some cases, 750 km.The most important characteristics of an earthquake are seismic energy and earthquake intensity.Seismic energy is the energy that is emitted from the hypocenter of an earthquake in the form of seismic waves. Seismic waves generated by earthquakes propagate in all directions from the source like sound waves, as they move away from it, their intensity decreases.
To measure the strength of earthquakes using the Richter scale. It characterizes the amount of energy that is released during an earthquake. The scale was proposed in 1935 by the American seismologist Charles Richter (1900–1985), theoretically substantiated together with the American seismologist Beno Gutenberg in 1941-1945. and received widespread throughout the world.
The Richter scale is a classification of earthquakes by magnitude (the quantity characterizing the energy released during an earthquake in the form of seismic waves), based on an estimate of the energy of seismic waves arising from earthquakes. Although the magnitude scale is not limited in principle, there are physical limits to the amount of energy released in the earth’s crust. Earthquakes of various magnitudes (on the Richter scale) are manifested as follows:
- 0 – the weakest felt tremors;
- 5 – the weakest shocks, leading to slight damage;
- 0 – moderate destruction;
- 5 – the strongest of the known earthquakes.
Scientists believe that earthquakes stronger than with a magnitude of 9.0, can not occur on Earth.
Since the magnitude characterizes the seismic energy output only at the earthquake epicenter, the concept of “earthquake intensity” was introduced to objectively assess the force of the earth’s surface oscillations at points remote from the epicenter [3, p. 57].
Earthquake intensity – the external effect of an earthquake on the Earth’s surface, which is expressed in a certain displacement of soil, rock particles, the degree of destruction of buildings, the appearance of cracks on the surface, etc. The intensity of earthquakes is measured in points.
There are several scales for determining the intensity of earthquakes. In 1902, a 12-point scale was developed in the USA, called the Merkalli scale (after the Italian volcanologist). This scale, somewhat modified, is now widely used by seismologists in the United States and several other countries. In Russia and some European countries, a 12-point international earthquake intensity scale (MSK-64) is used,
Public actions in case of an earthquake threat (based on the official website of the Russian Emergencies Ministry – URL: mchs.gov.ru/)
- Everyone who is in a seismic zone should be aware of the rules of conduct in the event of an earthquake, always be ready for action to survive, help loved ones and people who need help, and survive this natural disaster.
- A plan of action during an earthquake should be thought out in advance at home, at work, in a public place, on transport, and on the street.
- Explain to their family members what they should do during an earthquake, and teach them how to provide first aid.
- Documents, money, flashlight and spare batteries should be kept in a convenient place.
- At home there should be a supply of drinking water and canned food for a few days.
- Store hazardous substances (toxic chemicals, flammable liquids) in a safe, well-insulated place.
- All residents should know where the switch, gas and water taps are located in order to turn off electricity, gas and water if necessary.
The actions of the population during the earthquake
- Sensing the first vibrations of the building, seeing the swing of lamps, falling objects, hearing the rising roar and the sound of breaking glass, it is important not to panic.
- It is necessary to quickly leave the building, taking documents, money and basic necessities.
- Leaving the room, go down the stairs, not on the elevator.
- Once on the street, stay there, but do not stand near buildings, but go to open space. You need to stay away from the overhanging balconies, cornices, parapets, beware of dangling wires.
- It is very important to keep calm.
- If a person is forced to stay indoors, then it is necessary to stand in a safe place: against the inner wall, in the corner, in the inner wall opening, or at the carrier leg. If possible, hide the iodine table – it will protect from falling objects and debris, stay away from windows and heavy furniture. Do not use candles, matches, lighters – if a gas leak occurs, a fire may occur.
After the earthquake, it is necessary to provide first aid to injured and needy people. In all cases, it is necessary to obey the instructions of the local authorities, the headquarters for the elimination of the consequences of the disaster. We must be prepared for strong repeated shocks, since the first 2–3 hours after an earthquake are most dangerous.
If you are under the rubble, you must calmly assess the situation, if possible, provide yourself with medical assistance. You can try to connect with people outside the dam (voice, knock), you can use pipes and batteries, knock but which can spread over long distances.