The firmament has always been a symbol of security. And today, a person who is afraid of flying on an airplane feels protected only when he feels a flat surface under his feet. Therefore, it becomes the most terrible thing when, literally, the soil leaves from under your feet. Earthquakes, even the weakest ones, undermine the sense of security so much that many of the consequences are not of destruction, but of panic and are psychological, not physical. In addition, this is one of those catastrophes that mankind cannot prevent, and therefore many scientists are studying the causes of earthquakes, developing methods for fixing shocks, forecasting and warning. The amount of knowledge already accumulated by humanity on this issue allows minimizing losses in some cases. At the same time, the examples of earthquakes in recent years clearly indicate that there is still a lot to be learned and done.
The essence of the phenomenon
At the heart of everyoneearthquake is a seismic wave that sets the earth's crust in motion. It arises as a result of powerful processes of various depths. Rather minor earthquakes occur due to the drift of lithospheric plates on the surface, often along faults. Deeper in their location, the causes of earthquakes often have devastating consequences. They flow in zones along the edges of shifting plates that are subducting into the mantle. The processes taking place here lead to the most noticeable consequences.
Earthquakes happen every day, but people don't notice most of them. They are only fixed with special devices. At the same time, the greatest force of shocks and maximum destruction occur in the epicenter zone, places above the source that generated seismic waves.
Scales
Today there are several ways to determine the strength of the 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 still used today, but contrary to popular belief, each earthquake is assigned not points, but a certain magnitude.
Earthquake scores, which are always given in the description of the consequences, refer to a different scale. It is based on a change in the amplitude of the wave, or the magnitude of the fluctuations in the epicenter. ValuesThis scale also describes the intensity of earthquakes:
- 1-2 points: rather weak shocks, recorded only by instruments;
- 3-4 points: perceptible in high-rise buildings, often noticeable by chandelier swaying and small objects shifting, a person may feel dizzy;
- 5-7 points: shocks can be felt already on the ground, cracks may appear on the walls of buildings, plaster shedding;
- 8 points: powerful aftershocks cause deep cracks in the ground, visible damage to buildings;
- 9 points: walls of houses are destroyed, often underground structures;
- 10-11 points: such an earthquake leads to collapses 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 water movement in rivers.
Earthquake scores, which are given in various sources, are determined precisely on this scale.
Classification
The ability to predict any disaster comes 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 classification of earthquakes is based on the cause that caused it. Among the natural ones, tectonic, landslide, volcanic and others are distinguished. Let's dwell on them in more detail.
Tectonicearthquakes
The crust of our planet is constantly in motion. This is what causes most earthquakes. The tectonic plates that make up the crust move relative to each other, collide, diverge and converge. In places of faults, where plate boundaries pass and a compression or tension force arises, tectonic stress accumulates. Growing, sooner or later, it leads to the destruction and displacement of rocks, as a result of which seismic waves are born.
Vertical movements lead to the formation of failures or the uplift of rocks. Moreover, the displacement of the plates can be insignificant and amount to only a few centimeters, but the amount of energy released in this case is sufficient for serious destruction on the surface. Traces of such processes on earth are very noticeable. These can be, for example, displacements of one part of the field relative to another, deep cracks and dips.
Under the waters
The causes of earthquakes at the bottom of the ocean are the same as on land - movements of lithospheric plates. Their consequences for people are somewhat different. Very often, the displacement of oceanic plates causes a tsunami. Having originated above the epicenter, the wave gradually gains height and often reaches ten meters near the coast, and sometimes fifty.
According to statistics, over 80% of tsunamis hit the shores of the Pacific Ocean. Today, there are many services in seismic zones, working on predicting the occurrence and propagation of destructive waves and notifying the population aboutdanger. However, people are 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, images of red-hot magma eruption once seen appear in my head. And this is not surprising: two natural phenomena are interconnected. An earthquake can be caused by volcanic activity. The contents of the fiery mountains exert pressure on the surface of the earth. During the sometimes quite long period of preparation for the eruption, periodic explosions of gas and steam occur, which generate seismic waves. The pressure on the surface creates the so-called volcanic tremor (tremor). It is a series of small ground tremors.
Earthquakes are caused by processes occurring in the depths of both active volcanoes and extinct ones. In the latter case, they are a sign that the frozen fiery mountain can still wake up. Volcanic researchers often use micro-earthquakes to predict eruption.
In many cases it is difficult to unambiguously attribute an earthquake to a tectonic or volcanic group. The signs of the latter are the location of the epicenter in the immediate vicinity of the volcano and a relatively small magnitude.
Crashes
An earthquake can also be caused by rock collapse. collapsesand landslides in the mountains arise as a result of various processes in the bowels and natural phenomena, as well as human activity. Hollows and caves in the ground can collapse and generate seismic waves. The collapse of rocks is facilitated by insufficient drainage of water, which destroys seemingly solid structures. The collapse could also be caused by a tectonic earthquake. The collapse of an impressive mass at the same time causes minor seismic activity.
For such earthquakes, a small force is characteristic. As a rule, the volume of collapsed rock is not enough to cause significant vibrations. However, sometimes these types of earthquakes cause noticeable damage.
Classification by depth of occurrence
The main causes of earthquakes are associated, as already mentioned, with various processes in the bowels of the planet. One of the options for classifying such phenomena is based on the depth of their origin. Earthquakes are divided into three types:
- Surface - the source is located at a depth of no more than 100 km, about 51% of earthquakes belong to this type.
- Intermediate - the depth varies from 100 to 300 km, 36% of earthquakes are located on this segment.
- 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 center was located at a depth of more than 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 not dangerous for humans are used. Many data on the structure of the Earth were obtained as a result of studying the so-called Wadati-Benioff zone, which can be represented as a curved inclined line indicating the place where one tectonic plate enters 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 natural causes that cause tremors and seismic waves, artificial ones also appeared. A person, mastering nature and its resources, as well as increasing technical power, by his activity can provoke a natural disaster. The causes of earthquakes are underground explosions, the creation of large reservoirs, the extraction of large volumes of oil and gas, resulting in voids underground.
One of the rather serious problems in this regard is earthquakes arising from the creation and filling of reservoirs. Huge in terms of volume and mass, the water column exerts pressure on the bowels and leads to a change in the hydrostatic equilibrium in the rocks. At the same time, the higher the created dam, the greater the likelihood of the so-called induced seismic activity.
In places where earthquakes occur for natural reasons, often human activity is superimposed on tectonic processes and provokes the occurrence of naturaldisasters. Such data imposes a certain responsibility on companies involved in the development of oil and gas fields.
Consequences
Strong earthquakes cause great destruction over vast areas. The catastrophicity of the consequences decreases with distance from the epicenter. The most dangerous results of destruction are various man-made accidents. Collapse or deformation of industries associated with hazardous chemicals leads to their release into the environment. The same can be said about burial grounds and nuclear waste disposal sites. Seismic activity can cause contamination of vast areas.
In addition to the numerous destruction in cities, earthquakes have consequences of a different nature. Seismic waves, as already noted, can cause collapses, mudflows, floods and tsunamis. Earthquake zones after a natural disaster often change beyond recognition. Deep cracks and dips, soil erosion - these and other "transformations" of the landscape lead to significant environmental changes. They can lead to the death of the flora and fauna of the area. This is facilitated by various gases and metal compounds coming from deep faults, and simply by the destruction of entire sections of the habitat.
Strong and Weak
The most impressive destruction remains after mega-earthquakes. They are characterized by a magnitude of over 8.5. Such disasters, fortunately, are extremely rare. As a result of similar earthquakes in the distant past, some lakes were formedand riverbeds. A picturesque example of the "activity" of a natural disaster is Gek-Gol Lake in Azerbaijan.
Earthquakes that are 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 walls, swinging 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 collapses and landslides. The location of the sources of such earthquakes near a hydroelectric power station or nuclear power plant can also cause a man-made disaster.
Weak earthquakes are a hidden threat. As a rule, it is very difficult to find out about the probability of their occurrence on the ground, while phenomena of more impressive magnitude always leave identification marks. Therefore, all industrial and residential facilities near seismically active zones are under threat. Such structures include, for example, many nuclear power plants and power plants in the United States, as well as burial sites for radioactive and toxic waste.
Earthquake regions
The uneven distribution of seismically dangerous zones on the world map is also associated with the peculiarities of the causes of natural disasters. There is a seismic belt in the Pacific Ocean, with which, one way or another, an impressive part of earthquakes is connected. It includes Indonesia, the western coast of Central and South America, Japan, Iceland, Kamchatka, Hawaii, the Philippines, the Kuriles and Alaska. Secondaccording to the degree of activity, the belt is Eurasian: the Pyrenees, the Caucasus, Tibet, the Apennines, the Himalayas, Altai, the Pamirs and the Balkans.
The earthquake map is full of other areas of potential danger. All of them are associated with places of tectonic activity, where there is a high probability of collision of lithospheric plates, or with volcanoes.
The earthquake map of Russia is also full of a sufficient number of potential and active 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 disaster was almost eight points. The disaster led to the destruction of a large part of Neftegorsk.
The huge danger of a natural disaster and the impossibility of preventing it forces scientists around the world to study earthquakes in detail: the causes and consequences, "identification" signs and forecasting capabilities. Interestingly, technological progress, on the one hand, helps to more accurately predict terrible events, capture the slightest changes in the internal processes of the Earth, and on the other hand, it also becomes a source of additional danger: accidents at hydroelectric power plants and nuclear power plants, oil spills in places are added to the surface fractures. production, terrible in scale 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 is alive. According to scientists, completethe cessation of volcanic activity and earthquakes will mean the death of the planet in geological terms. The differentiation of the bowels will be completed, the fuel that has been heating the interior of the Earth for several million years will run out. And it is not yet clear whether there will be a place for people on the planet without earthquakes.
