Earthquake: The nature of phenomenon, types, and causes.
This essay will answer the questions of what an earthquake is, for what reasons it arises, and how dangerous it can be for a person.
Earthquakes are one of the most serious enemies of humankind, because of the nature of their origin and destructive potential. Depending on the strength of the tremors, destruction on the surface can reach catastrophic proportions. No matter how strong buildings and other human constructions are, everything can be destroyed by the force of nature.
About a million earthquakes occur on our planet every year. In most cases they do no harm to people and they are not even felt physically. But periodically, strong tremors occur that threaten the life of hundreds of humans (approximately every two weeks). Most earthquakes occur at the bottom of the ocean, which is the reason for the appearance of another natural phenomenon – the tsunami. A tsunami is no less dangerous, as it destroys everything in its path by a tidal wave. The danger arising from a tsunami occurs only in coastal areas and with a significant tremor, while earthquakes are dangerous for almost the entire planet.
An earthquake consists of earth tremors provoked by the processes that take place inside our planet. The seismic phenomenon occurs as a result of sharp displacements of the earth’s crust. This process can occur at great depths in the earth crust interior, but more often on the surface (up to 100 km).
Earthquakes are the final stage of the movement of terrestrial rocks. The frictional force prevents shifts in the earth’s crust, but when the stress reaches a critical level, a sharp shift occurs in the fracture of the rocks, and the energy of the frictional force finds a way out in motion and oscillations spread in all directions like sound waves. The place where the movement occurs is called the hypocenter (focus), and the point on the earth’s surface above the hypocenter is called the epicenter. As you move away from the epicenter, the strength of the seismic wave decreases. The speed of such waves can reach 7-8 km per second.
The causes of earthquakes are tectonic processes (associated with natural movement or deformation of the earth’s crust or mantle), volcanic processes, the filling of storage reservoirs, the collapse of underground mines, explosions, and other changes that are frequently provoked by human activities, which are called artificial pathogens.
Types of Earthquakes
Volcanic earthquakes occur as a result of high voltage in the volcano magma, due to movements of lava or volcanic gas. Such earthquakes don’t pose a great threat to humans, but they occur repeatedly and last a long time.
Man-caused earthquakes are a result of human activities, for example, in the case of flooding during the construction of large reservoirs, and during the extraction of oil or natural gas and coal, which is a violation of the integrity of the earth’s crust. Earthquakes in such cases don’t have large magnitudes, but can be dangerous for a small portion of the earth’s surface, and also provoke more serious tectonic changes, which increase stress in the planet’s crust.
The landslide earthquakes are caused by landslides themselves. They are not so dangerous and have a local character.
The strength (magnitude) of an earthquake is usually measured with a magnitude scale and intensity scale. The magnitude scale is the relative characteristic of an earthquake that has its own varieties: local magnitude, surface wave magnitude, magnitude of bulk waves, and moment magnitude. The most popular scale is the Richter local magnitude scale. In 1935, Charles Francis Richter proposed this method of measuring the strength of earthquakes, which gave the name to this scale. The Richter scale has a range from 1 to 9, magnitude is measured by a special device – a seismograph. The magnitude scale is often confused with a 12-point scale, which assesses the external manifestations of tremors (destruction, impact on people, natural objects). At the moment of the shock we first receive data about the magnitude scale, and after the earthquake, the earthquake’s force, which is measured on the intensity scale.
The intensity scale is a qualitative characteristic of the earthquake, indicating the nature and scale of this phenomenon in relation to people, animals, nature, and natural and artificial structures in the zone of earthquake damage.
In different countries the intensiveness of an earthquake is measured in different ways:
In Europe, the 12-point European Macroseismic scale is used.
In the United States, the 12-point Modified Mercalli intensity scale is used.
In Japan, the 7-point scale of the Japan Meteorological Agency seismic intensity scale (Shindo scale) is used.
In China, the 12-point scale of the China seismic intensity scale (CSIS) is used.
In Russia and some other countries, the 12-point scale of Medvedev–Sponheuer–Karnik scale is used.
Let’s see what these numbers mean, excluding the Japanese method of measuring:
3 points – minor fluctuations, which are noticed by very sensitive people, who are in rooms at the moment of the earthquake.
5 points – objects in the room start to move, and pushes are felt by everyone who is conscious.
6-7 points – high possibility of building destruction, cracks in the earth’s crust, and tremors are felt in any place and in any room.
8-10 points – buildings of almost any design begin to collapse, a person has difficulties to remain on his feet, possibly large cracks in the earth’s crust appear.
Logically thinking, one can roughly imagine that a smaller value on this scale bears less damage and the maximum may wipe everything out of existence.
What to Do in Case of an Earthquake?
In any case keep calm. Depending on the situation and course of events, take into account the following tips and recommendations for surviving the earthquake:
- Tell relatives, neighbors, and people on the street about the possible catastrophe, limiting with short phrases without unnecessary emotions, saving time and avoiding panic.
- If you are in a car, stop as soon as possible and don’t come out. Don’t stop near buildings, trees, overpasses, bridges, and power lines. Don’t come out from the car until the earthquake ends.
- If you are in a building, stand on the hard surface to avoid falling. Find a shelter, such as strong furniture that will protect you in case the walls fall. Make sure that the shakes have stopped and you are able to reach the exit. Hide your head and neck and move to the exit. Don’t turn on or off electrical devices. It may become a cause of fire.
- If you are in the street, stay in the same place if it’s safe. Look around and make sure that you have a safe place. Even the most earthquake-proof buildings may fall. Stay away from buildings, street lamps, power lines, and other buildings. Look for shelter near a hill, or in an open space.
1. Comerio. M. (2006). The Earthquake Emergency. Earthquake Protection, pp. 91-139.
2. Dowrick D.J. (2005). Design and Detailing of New Structures for Earthquake Ground Shaking. Earthquake Risk Reduction, pp. 313-427.
3. Spence, W., Sipkin, S. A., Choy G. L. (1989). Measuring the Size of an Earthquake. United States Geological Survey, p.45.
4. Watson, J., Watson, K. (1998, January 7). Volcanoes and Earthquakes. United States Geological Survey, p.23.
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