The earth at all times has been a symbol of security. And today, a person who is afraid of flying on an airplane feels protected only by feeling an even surface under his feet. Therefore, the worst thing is when, literally, the soil leaves under the feet. Earthquakes, even the weakest ones, undermine the sense of security so much that many consequences are associated not with destruction, but with panic and have a psychological rather than physical nature. In addition, this is one of those disasters that mankind is not able to prevent, and therefore many scientists are investigating the causes of earthquakes, developing methods for fixing tremors, forecasting and warning. The volume of knowledge already accumulated by mankind on this issue allows minimizing losses in some cases. At the same time, examples of earthquakes of recent years clearly indicate that there is still much to learn and do.
The essence of the phenomenon
Each earthquake is based on a seismic wave, which sets in motion the earth's crust. It arises as a result of powerful processes of various depths. Quite minor earthquakes occur due to drift of lithospheric plates on the surface, often along faults. The deeper in their location causes of earthquakes often have devastating consequences. They flow in zones along the edges of shifting plates, which are immersed in the mantle. The processes taking place here lead to the most noticeable consequences.
Earthquakes happen every day, but most of them people do not notice. They are only fixed with special devices. In this case, the greatest force of shocks and maximum destruction occur in the zone of the epicenter, places above the source that generated seismic waves.
Scales
Today, there are several ways to determine the strength of a phenomenon. They are based on such concepts as the intensity of an earthquake, its energy class and magnitude. The last of these is a value that characterizes the amount of energy released in the form of seismic waves. This method of measuring the strength of a phenomenon was proposed in 1935 by Richter and therefore is popularly called the Richter scale. It is used today, however, contrary to popular belief, not a point is assigned to each earthquake, but a certain magnitude.
The earthquake scores, which are always given in the description of the consequences, relate to a different scale. It is based on a change in the amplitude of the wave, or the magnitude of the oscillations in the epicenter. The values of this scale also describe the intensity of earthquakes:
- 1-2 points: rather weak tremors, recorded only by devices;
- 3-4 points: noticeable in high-rise buildings, often noticeable by the swaying of the chandelier and the displacement of small objects, a person may feel dizzy;
- 5-7 points: tremors can already be felt on the ground, cracks on the walls of buildings, shedding of plaster may occur;
- 8 points: powerful shocks lead to the appearance of deep cracks in the ground, noticeable damage to buildings;
- 9 points: the walls of houses are destroyed, often underground structures;
- 10-11 points: such an earthquake leads to landslides and landslides, the collapse of buildings and bridges;
- 12 points: leads to the most catastrophic consequences, up to a strong change in the landscape and even the direction of movement of water in the rivers.
Earthquake scores, which are given in various sources, are determined on this scale.
Classification
The ability to predict any catastrophe is associated with a clear understanding of what causes it. The main causes of earthquakes can be divided into two large groups: natural and artificial. The former are associated with changes in the bowels, as well as with the influence of some cosmic processes, the latter are caused by human activity. The earthquake classification is based on the cause of it. Among the natural ones, tectonic, landslide, volcanic and others are distinguished. Let us dwell on them in more detail.
Tectonic earthquakes
The crust of our planet is constantly in motion. It is it that underlies most earthquakes. The tectonic plates that make up the crust move relative to each other, collide, diverge and converge. In the places of faults, where the boundaries of the plates pass and a compression or tension force arises, tectonic stress accumulates. Growing, it, sooner or later, leads to the destruction and displacement of rocks, as a result of which seismic waves are generated.
Vertical movements lead to the formation of dips or the raising of rocks. Moreover, the displacement of the plates can be insignificant and amount to only a few centimeters, however, the amount of energy released in this case is enough for serious damage to the surface. Traces of such processes on earth are very noticeable. It can be, for example, displacements of one part of the field relative to another, deep cracks and dips.
Under the water column
The causes of earthquakes on the ocean floor are the same as on land - movements of lithospheric plates. Their effects on people are somewhat different. Very often, the displacement of oceanic plates causes tsunamis. Originating above the epicenter, the wave gradually gains height and often reaches ten meters, and sometimes fifty, near the coast.
According to statistics, over 80% of tsunamis fall on the shores of the Pacific Ocean. Today, there are many services in earthquake-prone zones, working on predicting the occurrence and propagation of destructive waves and alerting the public about the danger. However, man is still little protected from such natural disasters. Examples of earthquakes and tsunamis at the beginning of our century are another confirmation of this.
Volcanoes
When it comes to earthquakes, involuntarily in the head there are also once seen images of an eruption of red-hot magma. And this is not surprising: two natural phenomena are interconnected. Volcanic activity can cause an earthquake. The contents of the mountains of fire exert pressure on the surface of the earth. During a sometimes rather long period of preparation for an eruption, periodic explosions of gas and vapor occur, which generate seismic waves. Pressure on the surface creates the so-called volcanic tremor (trembling). It is a series of small tremors of the soil.
Earthquakes are caused by processes occurring in the bowels of both active volcanoes and extinct ones. In the latter case, they are a sign that the frozen mountain of fire may still wake up. Volcanic researchers often use microearthquakes to predict eruptions.
In many cases, it is difficult to unambiguously attribute an earthquake to a tectonic or volcanic group. Signs of the latter are the location of the epicenter in the immediate vicinity of the volcano and a relatively small magnitude.
Landslides
The cause of the earthquake can also be the collapse of rocks. Collapses and landslides in the mountains arise as a result of both various processes in the bowels and natural phenomena, as well as human activity. Fall and generate seismic waves can voids and caves in the earth. The collapse of the rocks contributes to insufficient water diversion, which destroys seemingly solid structures. The cause of the collapse may be a tectonic earthquake. The collapse of the impressive mass in this case causes insignificant seismic activity.
For such earthquakes, a small force is characteristic. As a rule, the volume of the crushed rock is not enough to cause significant fluctuations. Nevertheless, sometimes earthquakes of this type lead to noticeable damage.
Depth classification
The main causes of earthquakes are associated, as already mentioned, with various processes in the bowels of the planet. One of the classification options for such phenomena is based on the depth of their origin. Earthquakes are divided into three types:
- Surface - the focus is located at a depth of not more than 100 km, approximately 51% of earthquakes belong to this type.
- Intermediate - the depth varies in the range from 100 to 300 km, on this segment there are centers of 36% of earthquakes.
- Deep focus - below 300 km, this type accounts for about 13% of such disasters.
The most significant marine earthquake of the third type occurred in Indonesia in 1996. Its focus was located at a depth of over 600 km. This event allowed scientists to "enlighten" the bowels of the planet to a considerable depth. In order to study the structure of the subsoil, almost all deep-focus earthquakes that are harmless to humans are used. Many data on the structure of the Earth were obtained as a result of studying the so-called Vadati-Benioff zone, which can be represented as a curve of an inclined line indicating the place of entry of one tectonic plate under another.
Anthropogenic factor
The nature of earthquakes has changed somewhat since the beginning of the development of technical knowledge of mankind. In addition to the natural causes causing tremors and seismic waves, artificial ones also appeared. Man, mastering nature and its resources, as well as increasing technical power, can provoke a natural disaster through his activity. The causes of earthquakes are underground explosions, the creation of large reservoirs, the production of large volumes of oil and gas, resulting in emptiness under the ground.
One of the rather serious problems in this regard is the earthquakes arising from the creation and filling of reservoirs. Huge strata of water in volume and mass exert pressure on the bowels and lead to a change in hydrostatic equilibrium in the rocks. Moreover, the higher the created dam, the greater the likelihood of the appearance of the so-called induced seismic activity.
In places where earthquakes occur due to natural causes, often human activity is superimposed on tectonic processes and provokes the occurrence of natural disasters. Such data impose a certain responsibility on companies involved in the development of oil and gas fields.
Effects
Strong earthquakes lead to great damage in large areas. The catastrophic consequences decrease with distance from the epicenter. The most dangerous destruction results are various man-made accidents. The collapse or deformation of industries associated with hazardous chemicals leads to their release into the environment. The same can be said of the repositories and burial sites of nuclear waste. Seismic activity can cause infection of vast territories.
In addition to the numerous destruction in cities, earthquakes have consequences of a different nature. Seismic waves, as already noted, can cause landslides, mudflows, floods and tsunamis. Earthquake zones after a natural disaster often change beyond recognition. Deep cracks and dips, flushing of the soil - these and other "transformations" of the landscape lead to significant environmental changes. They can lead to the death of flora and fauna of the area. This is facilitated by various gases and metal compounds coming from deep faults, and simply the destruction of entire sections of the habitat.
Strong and weak
The most impressive damage remains after megaloesquakes. They are characterized by magnitude over 8.5. Such disasters are, fortunately, extremely rare. As a result of such earthquakes in the distant past, some lakes and riverbeds were formed. A picturesque example of the "activity" of a natural disaster is Lake Hek-Gol in Azerbaijan.
Earthquakes more modest in magnitude, leading to serious accidents and deaths, are called destructive and catastrophic. However, weak seismic activity can have impressive consequences. Such earthquakes cause cracking of the walls, swaying of chandeliers, etc. and, as a rule, do not lead to catastrophic consequences. They pose the greatest danger in the mountains, where they can cause serious landslides and landslides. The location of the centers of such earthquakes near the hydroelectric station or nuclear power plant can also cause a man-made disaster.
Weak earthquakes are a hidden threat. It is usually very difficult to find out about the probability of their occurrence on the ground, while phenomena that are more impressive in magnitude always leave identification marks. Therefore, all industrial and residential facilities near seismically active zones are at risk. Such structures include, for example, many nuclear power plants and power plants in the United States, as well as landfills for radioactive and toxic waste.
Earthquake areas
Unequal distribution of seismically dangerous zones on the world map is also associated with the peculiarities of the causes of natural disasters. In the Pacific Ocean, a seismic belt is located, with which, in one way or another, an impressive part of earthquakes is associated. It includes Indonesia, the west coast of Central and South America, Japan, Iceland, Kamchatka, Hawaii, the Philippines, the Kuril Islands and Alaska. The second most active zone is the Eurasian belt: the Pyrenees, the Caucasus, Tibet, the Apennines, the Himalayas, Altai, the Pamirs and the Balkans.
The earthquake map is also full of other areas of potential danger. All of them are associated with places of tectonic activity, where lithospheric plates are highly likely to collide, or with volcanoes.
The map of earthquakes in Russia is also full of a sufficient number of potential and existing sources. The most dangerous zones in this sense are Kamchatka, Eastern Siberia, the Caucasus, Altai, Sakhalin and the Kuril Islands. The most destructive earthquake in recent years in our country occurred on Sakhalin Island in 1995. Then the intensity of the natural disaster amounted to almost eight points. The catastrophe led to the destruction of a large part of Neftegorsk.
The tremendous danger of natural disaster and the impossibility of preventing it forces scientists around the world to study in detail earthquakes: the causes and consequences, "identification" signs and forecasting capabilities. It is interesting that technological progress, on the one hand, helps to more accurately predict terrible events, capture the slightest changes in the Earth’s internal processes, and on the other hand, it also becomes a source of additional danger: accidents at hydroelectric power stations and nuclear power plants, oil spills in places production, terrible in scope fires at work. The earthquake itself is a phenomenon as ambiguous as scientific and technological progress: it is destructive and dangerous, but it indicates that the planet lives. According to scientists, the complete cessation of volcanic activity and earthquakes will mean the death of the planet in geological terms. The differentiation of the bowels will end, the fuel will end, warming the Earth’s interior for several million years. And while it is not clear whether there will be a place for people on the planet without earthquakes.