Causes of earthquakes on planet earth. What is an earthquake and why does it occur Where does an earthquake occur

In times of high technology, established rhythms of life, people often forget that they do not manage everything to the end. And the manifestations of global events, such as earthquakes, are only in a few cases really noticeable. But if this cataclysm still reaches civilized corners, this event may remain a scar on people's memory for a long time.

How does an earthquake happen

Fluctuations of the earth's surface, as well as tremors, are the process of an earthquake. Scientists believe that the earth's crust consists of 20 huge plates. They move at a very low speed of about a few centimeters per year along the upper layer of the mantle. The boundaries between plates are often mountains or deep sea trenches. Where the plates crawl on top of each other, the edges are crumpled into folds. And in the crust itself, cracks are formed - tectonic faults, through which mantle matter seeps to the surface. Natural disasters such as earthquakes and volcanic eruptions often occur in these places. The divergence region of the shock wave sometimes extends for hundreds of kilometers.

Causes of an earthquake

• Collapses of a large mass of rock from the impact of groundwater often cause ground shaking at a short distance.
• In places of active volcanoes, under the pressure of lava and gases on the upper part of the crust, nearby territories are exposed to weak but prolonged shocks, often on the eve of an eruption.
• Technogenic activities of people - the construction of dams, the activity of the mining industry, the testing of nuclear weapons, accompanied by powerful underground explosions or the redistribution of internal masses of water.

How an earthquake occurs - earthquake sources

But not only the cause itself directly affects the power of the earthquake, but also the depth of the source of occurrence. The source or hypocenter itself can be located at any depth, from several kilometers to hundreds of kilometers. And it is a sharp displacement of large rock masses. Even with a slight shift, vibrations of the earth's surface will occur, and the range of their advancement will depend only on their strength and sharpness. But the farther the surface, the less devastating will be the consequences of the cataclysm. The point above the source in the ground layer will be the epicenter. And often subject to the greatest deformation and destruction during the movement of seismic waves.

How an earthquake occurs - zones of seismic activity

Due to the fact that our planet has not yet stopped its geological formation, there are 2 belts - the Mediterranean and the Pacific. The Mediterranean stretches from the Sunda Islands to the Isthmus of Panama. The Pacific covers Japan, Kamchatka, Alaska, moving on to the California mountains, Peru, Antarctica and many other places. There is constant seismic activity due to the formation of young mountains and volcanic activity.

How an earthquake occurs - the strength of an earthquake

The consequences of such terrestrial activity can be dangerous. There is a whole science for its study and registration - seismology. It uses several types of measurements of magnitude - a measure of the energy of seismic waves. The most popular Richter scale with a 10 point system.

• Less than 3 points are recorded only by seismographs due to their weakness.
• From 3 to 4 points, a person already feels slight swaying of the surface. The environment begins to react - the movement of dishes, the swinging of chandeliers.
• At 5 points, the effect is enhanced; in old buildings, interior decoration may crumble.
• 6 points can significantly damage old buildings, causing glass to rattle or crack in new houses, but they are already damaged at 7 points;
• 8 and 9 points cause significant destruction in large areas, collapses of bridges.
• The strongest magnitude 10 earthquakes are also the rarest and cause catastrophic damage.

• Living in high-rise buildings, you should understand that the lower the person is, the better, but you can’t use elevators during evacuation.
• It is worth leaving the buildings and moving away from them to a safe distance (turning off the electricity and gas), avoiding large trees and power lines.
• If there is no way to leave the premises, you need to move away from window openings and tall furniture or hide under a sturdy table or bed.
• While driving, it is better to stop and avoid high points or bridges.

Mankind cannot yet prevent earthquakes, or even predict in detail the reaction of the earth's crust to seismic shocks. Due to the huge number of variables, these are incredibly difficult forecasts. A person successfully passively defends himself in the form of strengthening buildings, improving the layout of infrastructure. This allows countries that are on the line of constant seismic activity to develop successfully.

A whole family of faults lurked under the Himalayas. Geologists have known this for a long time. The 2,400-kilometer Himalayan arc has the potential to devastate entire cities and villages in densely populated countries such as Pakistan, India and Bangladesh.

Potentially dangerous seismological zone

For a long time, Bhutan was not classified as a potentially dangerous seismological zone. Despite the fact that this country also extends along the arc, scientists did not assume that powerful earthquakes could occur here. However, a new study published in the journal Geophysical Research Letters suggests otherwise. In fact, the entire Himalayan arc is a seismogenic zone. This vast natural formation can experience rock ruptures at any time, including under Bhutan.

An unusual observation

So far, no detailed seismological records have been made in Bhutan. Employees of the University of Lausanne decided to fill this gap. Scientists found it very unusual that a country located in a potentially dangerous seismological zone has never experienced large-scale tremors in its history. An exception to the rule can be considered an earthquake of magnitude 6 points that occurred in 2006.

Buddhist Monk's Book

While trying to clarify the situation, the researchers accidentally stumbled upon the biography of a Buddhist monk and temple builder named Tenzin Lekpai Dondup. It is noteworthy that the historical document described powerful tremors that took place in this region in May 1714. Unfortunately, the monk in his notes did not specify exactly where the earthquake occurred.

What do other historical documents point to?

Swiss scientists got some clue and began to continue searching for documents hidden in historical archives. Thus, they managed to find out that a devastating earthquake with a magnitude of 7.5-8.5 on the Richter scale once occurred in the western part of Bhutan. Judging by the documents that were found, a 300-kilometer-long fault formed as a result of a natural disaster. If we compare these figures with the total length of the Himalayan arc, we can find a whopping 8 percent.

This conclusion is important. It once again indicates that the entire Himalayan arc throughout its history experienced powerful cataclysms. It is possible that destructive shocks will be repeated in the future. Now, for the first time, scientists can say publicly: Bhutan belongs to the number of potentially dangerous seismological zones.

Complex mountain structure

The Himalayan arc is an incredibly complex mountain structure. It was formed about 40 million years ago during the collision of India and Eurasia. It was a titanic tectonic battle that continues to this day. Thus, the most gigantic mountains on Earth were formed, which store a giant hot mantle under them. But that's not all. When two tectonic structures collided, a whole network of mobile chaotic faults was formed.

Over time, one of the biggest consequences of the “battle of the titans” was formed in the structure of the mountain range - the Main Himalayan deformation fault. This site is located along northern India and continues to pose a great danger to the surrounding areas. So, in April 2015, an earthquake of magnitude 7.8 occurred in Nepal. Devastating aftershocks then claimed the lives of more than 23 thousand people. This zone is classified as potentially dangerous due to the movement of plates at a speed of 2 centimeters per year.

Earthquake of the century

Another potential disaster zone lay on the border between the Hindustan and Eurasian lithospheric plates. Despite the fact that not a single major earthquake has been recorded here over the past 400 years, the movement of tectonic objects is also constantly ongoing. One of the plates gradually goes under the other. Someday there may be a magnitude 9 aftershock here that will endanger the population of 140 million Bangladesh. Scientists have already dubbed the coming catastrophe the "earthquake of the century."

Nature Under the earthquake refers to tremors and vibrations of the earth's surface, which are caused by natural or artificial causes. Today, an earthquake is one of the most difficult to predict and dangerous natural phenomena.

About a million earthquakes occur on our planet every year, but the vast majority of them are so weak that only special instruments (seismographs) register them.

Earthquakes cause rapid displacements of parts of the earth's crust. An earthquake begins with the movement of rocks or a gap in the depths of the earth's crust. This place is called the focus of an earthquake. Most often it is located at a depth of up to 100 kilometers, but sometimes the depth reaches 700 kilometers. The area of ​​land that is located above the focus of an earthquake is called the epicenter and experiences tremors of maximum strength. Seismic waves propagate from the source of an earthquake in all directions, which gradually fade away in the process of removal (this process is similar to the process of propagation of sound waves). The speed of propagation of seismic waves can reach 8 kilometers per second.

Most often, earthquakes occur at the bottom of the oceans, which is associated with a small thickness of the earth's crust in this area. These earthquakes are completely safe if they do not cause destructive tsunamis.

Earthquake forecasting is currently underway. This issue is most relevant for regions located at the junction of lithospheric plates, since the vast majority of destructive earthquakes occur here.

An earthquake can be caused not only by nature, but also by man. It is noted that tectonic activity is increasing in the areas of construction of large reservoirs, natural gas and oil production, the construction of large megacities from imported materials and the development of a large amount of rocks from quarries and mines. The reason for this is a violation of the natural balance and a change in pressure in the rocks.

Earthquakes are a natural phenomenon that even today attracts the attention of scientists not only due to their little knowledge, but also due to their unpredictability, which can harm humanity.

An earthquake is an earth tremor that can be felt by a person to a large extent, depending on the power of the earth's surface vibrations. Earthquakes are not uncommon and occur every day in different parts of the world.

Often, most earthquakes occur at the bottom of the oceans, which avoids catastrophic destruction within densely populated cities.

The principle of earthquakes

What causes earthquakes?

Earthquakes can be caused by both natural causes and man-made ones.

Most often, earthquakes occur due to faults in tectonic plates and their rapid displacement. For a person, the fault is not noticeable until the moment when the energy generated from the rupture of rocks begins to break out to the surface.

How do earthquakes occur due to unnatural causes?

Quite often, a person, through his negligence, provokes the appearance of artificial shocks, which in their power are not at all inferior to natural ones. Among these reasons are the following:

• — explosions;
• — overfilling of reservoirs;
• - ground (underground) nuclear explosion;
• mine collapses.

The place where the tectonic plate breaks is the focus of the earthquake. Not only the strength of the potential shock, but also its duration will depend on the depth of its location.

If the focus is located 100 kilometers from the surface, then its strength will be more than palpable. Most likely, this earthquake will entail the destruction of houses and structures.

Originating in the sea, such earthquakes cause tsunamis.

Where do earthquakes most often occur?

However, the focus can be located much deeper - 700 and 800 kilometers. Such phenomena are not dangerous and can be recorded only with the help of special instruments - seismographs.

The place where an earthquake is strongest is called the epicenter.

It is this piece of land that is considered the most dangerous for the existence of all living things.

Studying earthquakes

A detailed study of the nature of earthquakes makes it possible to prevent many of them and make the life of the population living in dangerous places more peaceful.

To determine the power and measure the strength of an earthquake, two basic concepts are used:

• — magnitude;
• - intensity;

The magnitude of an earthquake is a measure that measures the energy released during release from the source in the form of seismic waves.

The magnitude scale allows you to accurately determine the sources of fluctuations.

The intensity is measured in points and allows you to determine the ratio of the magnitude of shocks and their seismic activity from 0 to 12 points on the Richter scale.

Features and signs of earthquakes

Regardless of what causes an earthquake and in what area it is localized, its duration will be approximately the same.

One push on average lasts 20-30 seconds. But there are cases in history when a single push without repetition could last up to three minutes.

Signs of an approaching earthquake are the anxiety of animals, who, having sensed the slightest vibrations of the earth's surface, try to get away from the unfortunate place away.

Other signs of an imminent earthquake are:

• - the appearance of characteristic clouds in the form of oblong ribbons;
• — change of water level in wells;
• - failures in the operation of electrical equipment, mobile phones.

How to behave during earthquakes?

How to behave during an earthquake to save your life?

• - Maintain composure and calmness;
• - When indoors, never hide under fragile furniture, such as under a bed.

  Lie next to them in a fetal position and cover your head with your hands (or protect your head with something extra). When the roof collapses, it will fall on the furniture and a layer may form, in which you will find yourself. It is important to choose sturdy furniture whose widest part rests on the floor, i.e. this furniture cannot fall;

• - While outdoors, move away from tall buildings and structures, power lines that can collapse.
• - Cover your mouth and nose with a wet cloth to prevent dust and fumes from entering in case of fire of any object.

If you notice an injured person in a building, then wait for the tremors to end and only then make your way into the room.

Otherwise, both people may be trapped.

Where there are no earthquakes and why?

Earthquakes occur when tectonic plates break. Therefore, countries and cities located on a solid tectonic plate without faults can not worry about their safety.

Australia is the only continent in the world that is not located at the junction of lithospheric plates.

There are no active volcanoes and high mountains on it and, accordingly, there are no earthquakes. There are also no earthquakes in Antarctica and Greenland.

The presence of the enormous gravity of the ice shell prevents the spread of tremors over the surface of the earth.

The probability of earthquakes on the territory of the Russian Federation is quite high in rocky terrain, where the displacement and movement of rocks is most actively observed.

Thus, high seismicity is noted in the North Caucasus, Altai, Siberia and the Far East.

Report: Earthquakes

Earthquakes are tremors and vibrations of the earth's surface resulting from sudden displacements and ruptures in the earth's crust or the upper part of the mantle and are transmitted over long distances in the form of vibrations. The intensity of earthquakes is estimated in seismic points, magnitude is used for the energy classification of earthquakes (see Richter scale). The most famous catastrophic earthquakes: Lisbon 1755, California 1906, Messina 1908, Ashgabat 1948, Chile 1960, Armenian 1988, Iranian 1990.

General information

Strong earthquakes are catastrophic, yielding in the number of victims only to typhoons and significantly (tens of times) ahead of volcanic eruptions.

The material damage of one devastating earthquake can amount to hundreds of millions of dollars. The number of weak earthquakes is much greater than the number of strong ones. So, out of hundreds of thousands of earthquakes that occur annually on Earth, only a few are catastrophic. They release about 1020 J of potential seismic energy, which is only 0.01% of the thermal energy of the Earth radiated into outer space.

Where and why do earthquakes occur?

The territorial distribution of earthquakes is uneven.

It is determined by the movement and interaction of lithospheric plates.

Earthquake

The main seismic belt, in which up to 80% of all seismic energy is released, is located in the Pacific Ocean in the area of ​​deep-sea trenches, where cold lithospheric plates are moving under the continent. The rest of the energy is released in the Eurasian fold belt at the collision sites of the Eurasian plate with the Indian and African plates and in the areas of mid-ocean ridges under conditions of lithosphere extension (see Fig.

Rift world system).

Earthquake parameters

Earthquake sources are located at depths of up to 700 km, but most of the seismic energy (3/4) is released in sources located at depths of up to 70 km. The size of the focus of catastrophic earthquakes can reach 100 × 1000 km. Its position and the place where the masses begin to move (hypocenter) are determined by recording seismic waves that occur during earthquakes (for weak earthquakes, the focus and hypocenter coincide).

The projection of the hypocenter onto the earth's surface is called the epicenter. Around it is the area of ​​greatest destruction (epicentral, or pleistoseist, area).

Earthquake intensity

The intensity of the manifestation of earthquakes on the surface is measured in points and depends on the depth of the source and the magnitude of the earthquake, which serves as a measure of its energy.

The maximum known value of the magnitude approaches 9. The magnitude is related to the total energy of the earthquake, but this dependence is not direct, but logarithmic, with an increase in magnitude per unit, the energy increases by 100 times, i.e., with a shock with a magnitude of 6, 100 times more energy is released than at magnitude 5, and 10,000 more than at magnitude 4. Often in the media reporting on seismic disasters, the magnitude scale (Richter scale) and the seismic intensity scale, measured in seismic points, are identified.

j. Journalists reporting 12 on the Richter scale confuse magnitude with intensity. The intensity is the greater, the closer the source is to the surface, so, for example, if the source of an earthquake with a magnitude of 8 is located at a depth of 10 km, then on the surface the intensity will be 11-12 points; with the same magnitude, but at a depth of 40-50 km, the impact on the surface decreases to 9-10 points.

seismic scales

Seismic movements are complex, but classifiable.

There are a large number of seismic scales that can be reduced to three main groups. In Russia, the most widely used in the world 12-point scale MSK-64 (Medvedev-Sponheuer-Karnik), dating back to the Merkali-Cankani scale (1902), in Latin America, the 10-point Rossi-Forel scale (1883) is adopted, in Japan - 7-point scale.

The assessment of intensity, which is based on the everyday consequences of an earthquake, easily distinguishable even by an inexperienced observer, is different in the seismic scales of different countries. For example, in Australia, one of the degrees of shaking is compared with “how a horse rubs against a veranda post”, in Europe the same seismic effect is described as “bells begin to ring”, in Japan there is an “overturned stone lantern”.

In the simplest and most convenient form, sensations and observations are presented in a schematized short descriptive scale (MSK variant) that anyone can use.

Point - Manifestation on the surface

1 - Not felt by anyone, recorded only by seismic instruments

2 - Felt sometimes by people who are in a calm state

3 - Felt by few, more pronounced indoors on higher floors

4 - Felt by many (especially indoors), at night some wake up.

Possible ringing of dishes, rattling of glasses, slamming of doors

5 - Felt by almost everyone, many wake up at night. Swinging hanging objects, cracks in window panes and plaster

6 - Felt by everyone, plaster crumbles, light destruction of buildings

7 - Cracks in the plaster and chipping of individual pieces, thin cracks in the walls. Shocks are felt in cars

8 - Large cracks in the walls, falling pipes, monuments.

Cracks on steep slopes and on damp soil

9 - Collapse of walls, roof slabs in some buildings, breaks in underground pipelines

10 - The collapse of many buildings, the curvature of the railroad tracks.

Landslides, collapses, cracks (up to 1 m) in the ground

11 - Numerous wide cracks in the ground, landslides in the mountains, collapse of bridges, only a few stone buildings remain stable

12 - Significant changes in the relief, deviation of the flow of rivers, objects thrown into the air, total destruction of structures

How far does an earthquake affect

Strong earthquakes can be felt at a distance of a thousand or more kilometers.

Thus, in aseismic Moscow, shocks with an intensity of up to 3 points are observed from time to time, serving as an “echo” of catastrophic Carpathian earthquakes in the Vrancea mountains in Romania, the same earthquakes in Moldova, close to Romania, are felt as 7-8 points.

Earthquake duration

The duration of earthquakes is different, often the number of tremors forms a swarm of earthquakes, including previous (foreshocks) and subsequent (aftershocks) shocks.

The distribution of the strongest shock (the main earthquake) within the swarm is random. The magnitude of the strongest aftershock is 1.2 less than that of the main shock, these aftershocks are accompanied by their secondary series of subsequent shocks.

For example, an earthquake that occurred on about. Lissa in the Mediterranean, lasted three years, the total number of shocks for the period 1870-73 amounted to 86 thousand.

catastrophic earthquakes

Of the huge number of earthquakes that occur annually, only one has a magnitude equal to or greater than 8, ten - 7-7.9, one hundred - 6-6.9.

Any earthquake with a magnitude of St. 7 could be a major disaster. However, it can also go unnoticed if it occurs in a desert area. So, the grandiose natural disaster - the Gobi-Altai earthquake (1957; magnitude 8.5, intensity 11-12 points) - remains almost unexplored, although due to the enormous force, small depth of the source and lack of vegetation cover, this earthquake left on the surface the most a complete and diverse picture (2 lakes appeared, a huge overthrust in the form of a stone wave up to 10 m high instantly formed, the maximum displacement along the fault reached 300 m, etc.).

P.). An area 50-100 km wide and 500 km long (like Denmark or Holland) was completely destroyed. If this earthquake had occurred in a densely populated area, the number of victims could have been measured in the millions. The consequences of one of the strongest earthquakes (magnitude could be 9), which occurred in the oldest region of Europe - Lisbon - in 1755 and captured the territory of over 2.5 million km2, were so grandiose (50 thousand out of 230 thousand people died).

townspeople, a rock grew in the harbor, the coastal bottom became dry land, the outline of the coast of Portugal changed) and impressed the Europeans so much that Voltaire responded to him with “The Poem on the Death of Lisbon” (1756, Russian translation 1763). Apparently, the impression of this catastrophe was so strong that Voltaire in the poem challenged the doctrine of pre-established world harmony.

Strong earthquakes, no matter how rare they are, never leave contemporaries indifferent. Thus, in W. Shakespeare's tragedy "Romeo and Juliet" (1595), the nurse recalls the earthquake of 1580, which, apparently, the author himself experienced.

Why do people die in earthquakes?

If earthquakes occur at sea, they can cause destructive waves - tsunamis, which most often devastate the coasts of the Pacific Ocean, as happened in 1933 in Japan and in 1952 in Kamchatka.

The total number of victims of earthquakes on the planet over the past 500 years amounted to about 5 million people.

people, almost half of them are in China. So in 1556 in the Chinese Prov. An earthquake with a magnitude of 8.1 killed 830,000 people in Shaanxi; according to official Chinese data (according to American seismologists, up to 1 million people). Exceptionally severe consequences were also connected with the earthquakes in 1737 in Calcutta (India), when 300,000 people died.

people, in 1908 in Messina (Italy) - 120 thousand people, in 1923 in Tokyo - 143 thousand people.

Large earthquake losses are usually associated with high population density, primitive construction methods, especially characteristic of poor areas, and it is not at all necessary that the earthquake be strong (for example, in 1960 as a result of a seismic shock with a magnitude of 5.8 up to 15 thousand died

man in Agadir, Morocco). Natural phenomena - landslides, cracks play a smaller role. The catastrophic consequences of an earthquake can be prevented by improving the quality of buildings, since most of the people die under their rubble. It is also useful to take advice - during an earthquake, do not run out into the street, but rather take cover in a doorway or under a strong slab or board (table) that can withstand the weight of a falling load.

Forecast and zoning of earthquakes

The task of earthquake forecasting based on observations of precursors (prediction not only of the place, but, most importantly, the time of a seismic event) is far from being solved, because

to. none of the harbingers can be considered reliable. Isolated cases of exceptionally successful timely forecasts are known, for example, in 1975 in China, an earthquake with a magnitude of 7.3 was very accurately predicted. In earthquake-prone areas, the construction of earthquake-resistant structures plays an important role (see.

anti-seismic construction). The division of the territory according to the degree of potential seismic hazard is part of the task of seismic zoning. It is based on the use of historical data (on the recurrence of seismic events, their strength) and instrumental observations of earthquakes, geological and geographical mapping and information about the movement of the earth's crust.

The zoning of the territory is also connected with the problem of insurance against earthquakes.

Seismograph

Instrumental observations first appeared in China, where in 132 Chang Heng invented a seismoscope, which was a skillfully made vessel.

On the outer side of the vessel, with a pendulum placed inside, the heads of dragons were engraved in a circle, holding balls in their mouths. When the pendulum was swinging from an earthquake, one or more balls fell into the open mouths of the frogs, placed at the base of the vessels so that the frogs could swallow them.

A modern seismograph is a set of instruments that record ground vibrations during an earthquake and convert them into an electrical signal recorded on seismograms in analog and digital form. However, as before, the main sensitive element is a pendulum with a load.

seismic service

Permanent observations of earthquakes are carried out by the seismic service.

The modern world network includes St. 2000 stationary seismic stations, whose data are systematically published in seismological bulletins and catalogs.

In addition to stationary stations, expeditionary seismographs are used, including those installed at the bottom of the oceans. Expeditionary seismographs were also sent to the Moon (where 5 seismographs annually record up to 3000 moonquakes), as well as to Mars and Venus.

Anthropogenic earthquakes

20th century man-made human activity, which has taken on a planetary scale, has become the cause of induced (artificially induced) seismicity, which occurs, for example, during nuclear explosions (tests at the Nevada test site initiated thousands of seismic shocks), during the construction of reservoirs, the filling of which sometimes provokes strong earthquakes.

This happened in India, when the construction of the Koyna reservoir caused an 8-magnitude earthquake, in which 177 people died.

Studying earthquakes

Seismology is the study of earthquakes.

Seismic waves generated during earthquakes are also used to study the internal structure of the Earth, achievements in this area have served as the basis for the development of seismic exploration methods.

Earthquakes have been observed since ancient times. Detailed historical descriptions, reliably testifying to earthquakes from ser.

1 thousand BC e., given by the Japanese. Great attention was also paid to seismicity by ancient scientists - Aristotle and others. Systematic instrumental observations begun in the 2nd half. 19th century led to the separation of seismology into an independent science (B.

B. Golitsyn, E. Wiechert, B. Gutenberg, A. Mohorovichich, F. Omori and others).

EARTHQUAKE MAGNITUDE (from lat. magnitudo - magnitude), a conditional value that characterizes the total energy of elastic vibrations caused by earthquakes or explosions; allows you to compare the sources of oscillations by their energy.

SEISMIC SCALE, a scale for assessing the intensity of an earthquake on the Earth's surface. The Russian Federation uses the 12-point seismic scale MSK-64.

MIDDLE OCEANIC RIBS, mountain structures that form a single system at the bottom of the World Ocean, encircling the entire globe.

LITHOSPHERIC PLATE, large (several thous.

km in diameter) a block of the earth's crust, including not only the continental, but also the oceanic crust associated with it; bounded on all sides by seismically and tectonically active fault zones.

HYPOCENTRE, the point of the beginning of the movement of masses (rupture rupture) in the source of the earthquake. Depth up to 700 km.

2017 Reference books. Mobile version.

12-point scale of intensity, strength of earthquakes

Earthquake intensity- a qualitative characteristic of the degree of destruction and other manifestations on the earth's surface, at a specific point on the earth's surface.

How does an earthquake happen

For this, a twelve-point scale is used, in contrast to the nine-point magnitude scale (Richter scale), which quantitatively characterizes the energy in the earthquake source.

Earthquake gradation by strength (intensity, seismic effect):

One point - minimal seismicity, not felt by people.

Two points (very weak) - weak vibrations are noticeable on the upper floors of high-rise buildings.

The reason may be man-made, from a loaded truck passing under the windows.

Three ball. (weak) - chandeliers swing.

Score four (moderate) - Shaking is felt inside buildings.

Five points (strong) - vibrations are felt both in the building and on the street.

Six points - furniture moves and falls, dishes bounce, window panes burst.

People, frightened, run out of the buildings into the street.

Seven points (very strong) - it is difficult to stand on your feet, the walls of brick houses are cracking, flights of stairs and ceilings of buildings are falling, landslides and cracks appear on roads, in winter - ice is cracking on rivers and reservoirs.

There is an additional danger - fires, accidents, short circuits.

Eight points. (destructive) - brick buildings are collapsing, underground communications are torn.

Nine points (destructive) - cracks form in the soil, on rivers and in reservoirs - great excitement.

Ten points. (destructive) - asphalt on the roads is crushed and broken, cracks in the ground - up to a meter wide, landslides and collapses.

Eleven points (catastrophic) - almost all brick houses are destroyed, roads are badly damaged.

Twelve points (catastrophic) - the earth's surface is changing; cracks in the earth's crust reach a width of up to 10-15 m, depth - up to 10 m or more, closing or remaining open during the next shocks; the amplitude of vertical oscillations of the soil reaches half a meter; large areas subside and can be flooded, or rise up with an amplitude of up to several tens of meters or more; displacement occurs along the faults.

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earthquake called tremors and vibrations of the surface of the planet, arising in the upper layers of the lithosphere due to a sharp displacement of the lithospheric plates. The least dangerous of them are formed in the Earth's mantle (at great depths). But ruptures and displacements of the surface layer can bring with them catastrophic destruction.

This is explained by a decrease in the strength of earthquakes with distance from its source. The deeper the focus is, the smaller the oscillations occur on the earth's surface.

The strength of earthquakes in points

The focus of an earthquake (the place where it formed) is also called the focus or hypocenter.

From it diverge in all directions seismic waves, like waves on water arising from a thrown pebble, with the only difference that seismic waves are directed both to the sides, and up, and down. But that place on the earth's surface, which is located directly above the hearth itself, is called earthquake epicenter. As a rule, the strongest vibrations occur precisely in it.

The magnitude scale is able to assess the strength of this destructive natural phenomenon.

To be more precise, it estimates the energy that is released in the form of seismic waves. And this value fluctuates 1 to 9.5(it is usually used by scientists, for example, in the popular film "The San Andreas Fault" the magnitude reaches a maximum value of 9.5).
But although this characteristic is quite eloquent, nevertheless, this is not enough to understand how dangerous a cataclysm is.

After all, it happens that a weaker, but prolonged earthquake causes much more damage than a strong one. Therefore, there is also a scale of intensity. It evaluates the impact of vibrations on the earth's surface, as well as their consequences.

To assess this destructive phenomenon, various scales are used, but, as a rule, they are all 12-point. The most popular magnitude scale is Richter scale. If we compare it with the intensity scale, then we can roughly imagine the consequences of earthquakes of various strengths:

• 1-2 points - it is noted only on devices, although especially sensitive people can feel weak tremors.
• 3-4 points - felt by almost everyone as light shocks, especially noticeable inside buildings (by light rattling of objects and shaking).
• 5-6 points - quite strong fluctuations occur, during which cracks may appear in old houses, plaster crumbles, objects fall from shelves, etc.
• 7-8 points - very strong vibrations are observed, leading to the destruction of houses and the appearance of cracks in the ground.
• 9-10 points - a devastating earthquake, leading to the destruction of buildings, landslides and collapses, huge cracks in the earth's surface, etc.

  Phenomena of such strength are observed about 10 times a year.

• 11-12 points - a catastrophic earthquake, the devastating consequences of which are difficult to predict. They usually happen once a year.

The consequences of earthquakes

Strong earthquakes can destroy buildings and various structures. As a result of such destruction, many people die.

And if the focus is in the sea, then a tsunami falls on the coast (a huge wave that can sweep away everything in its path). An earthquake is one of the most dangerous phenomena on our planet. And given that they are almost impossible to predict, like many other phenomena ... This becomes a real problem.

Earthquakes. Why earthquakes happen

Earthquake statistics

As we already know, earthquakes with a magnitude of 7-12 are called dangerous. It is they who are able to lead to destruction and change in the relief of the planet. And although it is impossible to say exactly how many such phenomena occur annually, we can calculate the approximate number of the most powerful of them.

Two centuries ago, for example, there were about 40 earthquakes a year with a strength of 7 or more. Now their number has increased tenfold. 400 strong earthquakes a year for the Earth have already become the norm. The trend is impressive, isn't it? And what will happen next?

earthquakes

Earthquakes are tremors accompanied by vibrations of the earth's surface.

Causes and types

The location of earthquake sources practically coincides with the boundaries of lithospheric plates

Earthquakes are tectonic, volcanic and landslide.

Tectonic earthquakes arise due to sharp displacements of mountain plates or as a result of the withdrawal of an oceanic platform under the mainland.

After all, the surface of the earth consists of continental and oceanic platforms, which, in turn, consist of separate blocks. When the blocks are on top of each other, they can rise up and mountains are formed, or they can go down and depressions are formed, or one of the plates will go under the other.

All these processes are accompanied by vibrations or tremors of the earth.

Volcanic earthquakes occur due to the fact that flows of hot lava and gases press from below on the surface of the Earth and thus make you feel that the earth is moving away from under your feet. Volcanic earthquakes are usually not very strong, but can last quite a long time, sometimes several weeks.

Often such earthquakes warn of an imminent volcanic eruption, which is even more dangerous than the earthquake itself.

Sometimes voids form underground, for example, under the influence of groundwater or underground rivers that erode the earth. In these places, the ground cannot withstand its own weight and collapses, causing a slight shaking.

It is called landslide earthquake.

After strong earthquakes, the landscape of the area changes, new lakes and mountains may appear

The most destructive and terrible are tectonic earthquakes. The place where a collision of plates or a powerful explosion occurs, associated with the release of energy accumulated in the earth, is called earthquake focus, or hypocenter.

When the explosion occurs, a shock wave with a speed of more than 5 km / s (depending on the power of the explosion) begins to spread in all directions, reaches the surface of the earth (this area on the surface is called the epicenter, and it is located directly above the hypocenter) and diverges to the sides along circles.

In the epicenter, the most severe destruction occurs, and on the outskirts of the area affected by the earthquake, people may not even feel anything.

The strength of earthquakes

Earthquakes are one of the most dangerous natural phenomena. They bring great destruction and disaster, destroying not only material values, but also all living things, including people.

The strength of an earthquake on the earth's surface is measured in points on a special 12-point scale.

Destruction after a strong earthquake

Point scale for measuring the strength of an earthquake:

• 1 point - Not felt.

  It is noted only by special devices

• 2 point - Very weak, noted only by pets and some people in the upper floors of buildings
• 3 ball - Weak. Only felt inside some buildings, like a concussion when driving a truck
• 4 ball - Moderate. You can hear the creaking of floorboards, beams, the clinking of dishes, the trembling of furniture.

  Inside the building, shaking is felt by most people.

• 5 ball - Pretty strong. In the rooms, shocks are felt as from the fall of heavy objects. Window panes burst, chandeliers and furniture sway
• 6 ball - Strong. Heavy furniture sways, dishes break, books fall from shelves, only very dilapidated houses are destroyed.
• 7 ball - Very strong.

  Old houses are destroyed. Cracks appear in strong buildings, plaster crumbles. Cloudy water in rivers and lakes

• 8 ball - Destructive. Trees sway violently, strong fences break. Many strong buildings are destroyed. Cracks appear in the soil
• 9 ball - Devastating. Strong buildings are destroyed.

  earthquakes

  Significant cracks appear in the soil

• 10 ball - Destroying. Even strong buildings and bridges are destroyed. Landslides and collapses, cracks and bends in the soil occur
• 11 ball - Catastrophe. Almost all stone buildings, roads, dams, bridges are destroyed. Shear cracks form on the surface of the earth
• 12 ball - Strong catastrophe. All structures are destroyed, the whole area is devastated.

  riverbeds are changing

Seismology

The pen of a seismograph draws a curved line in the form of sharp zigzags when tremors begin

Earthquakes are studied by science seismology. In different countries of the world, scientists conduct observations on the behavior of the earth's crust. In this they are helped by special devices - seismographs.

They measure and automatically record the smallest tremors occurring anywhere in the world. When the earth's surface oscillates, the main part of the seismograph - the suspended load - due to inertia moves relative to the base of the device, and the recorder records the seismic signal transmitted to the marker.

An important task of seismology is the prediction of earthquakes.

Unfortunately, modern science cannot yet accurately predict them. Seismologists can more or less reliably determine the area and strength of an earthquake, but it is very difficult to predict its beginning.

Can an earthquake rock the earth?

In mid-May 1960, one of the most significant and destructive earthquakes occurred in Chile - the Great Chilean Earthquake.

Despite the fact that the main ground vibrations occurred in the southwestern part of South America - the epicenter of the earthquake was located near the city of Valdivia - their "echoes" reached other territories of our planet: in particular, the Hawaiian Islands and Japan. The phenomenon in which an earthquake that occurred in one part of the earth causes other parts of the earth to pulsate and tremble, even those located thousands of kilometers from the epicenter, is called the "swing" or "vibration" of the earth.

The fear and helplessness of people who have felt the vibrations of the earth's surface is so great that knowledge about the origin of earthquakes is always in demand.

Why do earthquakes happen?

There are few reasons - just two. The first is related to the work of the so-called Internal Forces of the Earth. The second is human activity. This type of earthquakes appeared quite recently, but their intensity, expressed in balls, is ready to "compete" with the Natural tremors of the "terrestrial firmament".

Earthquakes created by nature

The origin of natural earthquakes is easily superimposed on Wegener's theory of the movement of lithospheric plates. Concisely, it looks like this - the earth's crust is broken into giant plates. A bit like a cracked shell on a hard-boiled egg. Only the lithospheric plates are much larger. At the same time, they are not rigidly fixed, but constantly move one relative to the other.

Movement can be in horizontal and vertical direction. This is possible due to the fact that the blocks of the earth's crust are located on a plasma-like, relatively liquid layer of magma - the asthenosphere.

And now the most important thing is that any interaction of lithospheric plates is accompanied by the processes of tectonism, volcanism and seismism. Particularly strong shaking of the earth's crust occurs during fast horizontal movements - counter and discontinuous.

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Probable zones of earthquake manifestation

It follows from this that potential places with the maximum probability of earthquakes will be at the junctions of lithospheric plates. That's right - the main seismological stations are located along the Pacific Ring of Fire, the Atlantic and Alpine-Himalayan seismic belts.

The Pacific Ring of Fire is the area of ​​interaction of the earth's crust lining the bottom of the Pacific Ocean with the Eurasian, Indo-Australian, Antarctic, South American and North American lithospheric plates. Very active. It was in her area of ​​​​responsibility that the devastating earthquake in Jamaica in 1692, the Japanese “Earthquake of the Hoei years” in 1707, the Great Chilean in 1960 and Alaska in 1964 occurred.

Atlantic - the line of contact of the Eurasian, African-Arabian, South American and North American platforms.

The Alpine-Himalayan seismic belt is a very active one, formed at the junction of the African-Arabian, Indo-Australian and Eurasian platforms. The most destructive earthquakes are Ganja in 1139, Sicilian in 1693, Assam in 1897, Messina in 1908, Crimean in 1927. Ashgabat 1948, Tashkent 1966 and Spitak 1988.

In addition to earthquakes and "attacks" of some lithospheric plates on others, seismic phenomena are accompanied by volcanism. And if the contact zone is within the limits of the World Ocean, then tsunami-type waves arise.

Related materials:

Can an earthquake be predicted?

Earthquakes caused by volcanic activity deserve a separate proposal. That is, they are formed in the same zones of interaction of lithospheric plates. But they are initiated by the tension that arises in the depths of volcanoes. The intensity of such fluctuations is small, but they are multiple and delayed in time. The earth's crust can be shaken for weeks, months.

Man-made earthquakes

In the twentieth century, new earthquakes appeared - anthropogenic. First, those caused by human industrial activity. For example, voids in mines or oil-bearing horizons, which reduce the established strength of existing rocks, which leads to the activation of seismic processes.

Secondly, some states use the same underground voids as a place for testing weapons, which causes earthquakes. Thirdly, there are projects to create artificial oscillations of the earth's crust, which are considered as a tectonic weapon.

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It seems that natural disasters happen once every hundred years, and our vacation in one or another exotic country lasts only a few days.

The frequency of earthquakes of different magnitudes in the world per year

• 1 earthquake with a magnitude of 8 or more
• 10 - with a magnitude of 7.0 - 7.9 points
• 100 - with a magnitude of 6.0 - 6.9 points
• 1000 - with a magnitude of 5.0 - 5.9 points

Earthquake intensity scale

Richter scale, points	Force	Description
	Not felt	Not felt
	Very weak kicks	Felt only by very sensitive people
		Felt only inside some buildings
	intensive	Perceived by the slight vibration of objects
	Pretty strong	Felt by sensitive people on the street
		Felt by everyone on the street
	Very strong	Cracks may appear in the walls of stone houses
	destructive	Monuments are being moved, houses are badly damaged
	devastating	Severe damage or destruction of houses
	Destroying	Cracks in the ground can be up to 1m wide
	Catastrophe	Cracks in the ground can reach more than a meter. Houses are almost completely destroyed
	Catastrophe	Numerous cracks in the ground, collapses, landslides. The emergence of waterfalls, the deviation of the flow of rivers. No building can withstand

Mexico City, Mexico

One of the most densely populated cities in the world is known for its insecurity. In the 20th century, this part of Mexico experienced the force of more than forty earthquakes, the magnitude of which exceeded 7 on the Richter scale. In addition, the soil under the city is saturated with water, which makes high-rise buildings vulnerable to natural disasters.

The most devastating were the tremors of 1985, when about 10,000 people died. In 2012, the epicenter of the earthquake fell on the southeastern part of Mexico, but the vibrations were well felt in Mexico City and Guatemala, about 200 houses were destroyed.

2013 and 2014 were also marked by high seismic activity in different parts of the country. Despite all this, Mexico City is still attractive for tourists due to its picturesque landscapes and numerous monuments of ancient culture.

Concepcion, Chile

Chile's second largest city, Concepción, located in the heart of the country near Santiago, regularly becomes a victim of aftershocks. In 1960, the famous Great Chilean earthquake with the highest magnitude in history of 9.5 destroyed this popular Chilean resort, as well as Valdivia, Puerto Montt, etc.

In 2010, the epicenter was again located near Concepción, about one and a half thousand houses were destroyed, and in 2013 the focus submerged to a depth of 10 km off the coast of central Chile (magnitude 6.6 points). However, today Concepción does not lose popularity among both seismologists and tourists.

Interestingly, the elements haunt Concepción for a long time. At the beginning of its history, it was located in Penko, but due to a series of devastating tsunamis in 1570, 1657, 1687, 1730, the city was moved slightly south of its former location.

Ambato, Ecuador

Today, Ambato attracts travelers with its mild climate, beautiful landscapes, parks and gardens, and massive fruit and vegetable fairs. The old buildings of the colonial era are intricately combined here with new buildings.

Several times this young city, located in the central part of Ecuador, two and a half hours drive from the capital Quito, was destroyed by earthquakes. The most powerful were the aftershocks of 1949, which razed many buildings to the ground and claimed more than 5,000 lives.

Recently, the seismic activity of Ecuador has persisted: in 2010, an earthquake of magnitude 7.2 occurred southeast of the capital and was felt throughout the country, in 2014 the epicenter moved to the Pacific coast of Colombia and Ecuador, however, in these two cases there were no casualties .

Los Angeles, USA

Predicting devastating earthquakes in Southern California is a favorite pastime for geoscientists. The fears are justified: the seismic activity of this area is associated with the San Andreas Fault, which runs along the Pacific coast through the state.

History remembers the most powerful earthquake of 1906, which claimed 1500 lives. In 2014, the sunny year managed to survive twice the tremors (magnitude 6.9 and 5.1 points), which affected the city with minor destruction of houses and a severe headache for residents.

True, no matter how much seismologists frighten with their warnings, the “city of angels” Los Angeles is always full of visitors, and the tourist infrastructure here is incredibly developed.

Tokyo, Japan

It is no coincidence that the Japanese proverb says: "Earthquakes, fires and the father are the worst punishments." As you know, Japan is located at the junction of two tectonic layers, the friction of which often causes both small and extremely destructive tremors.

For example, in 2011, the Sendai earthquake and tsunami near Honshu (magnitude 9) killed more than 15,000 Japanese. At the same time, the people of Tokyo are already accustomed to the fact that several earthquakes of minor magnitude occur every year. Regular fluctuations impress only visitors.

Despite the fact that most of the buildings of the capital were built taking into account possible shocks, in the face of powerful cataclysms, residents are defenseless.

Repeatedly in its history, Tokyo has disappeared from the face of the earth and rebuilt again. The great Kanto earthquake of 1923 turned the city into ruins, and after 20 years, rebuilt, it was destroyed by a large-scale bombing by American air forces.

Wellington, New Zealand

Wellington, the capital of New Zealand, seems to be created for tourists: it has many cozy parks and squares, miniature bridges and tunnels, architectural monuments and unusual museums. People come here to participate in the grandiose festivals of the Summer City Program and admire the panoramas that became the set of the Hollywood trilogy The Lord of the Rings.

Meanwhile, the city was and remains a seismically active zone, year after year experiencing tremors of varying strength. In 2013, a magnitude 6.5 earthquake struck just 60 kilometers away, causing power outages in many parts of the country.

In 2014, Wellington residents felt tremors in the northern part of the country (magnitude 6.3).

Cebu, Philippines

Earthquakes in the Philippines are a fairly common occurrence, which, of course, does not in the least frighten those who like to lie on the white sand or swim with a mask and snorkel in clear sea water. During the year, on average, there are more than 35 earthquakes with a magnitude of 5.0-5.9 points and one with a magnitude of 6.0-7.9 points.

Most of them are vibration echoes, the epicenters of which are located deep under water, which creates the danger of a tsunami. The tremors of 2013 claimed more than 200 lives, led to serious destruction in one of the most popular resorts of Cebu and in other cities (magnitude 7.2).

Employees of the Philippine Institute of Volcanology and Seismology are constantly monitoring this seismic zone, trying to predict future cataclysms.

Sumatra Island, Indonesia

Indonesia is considered to be the most seismically active region in the world. In recent years, it has managed to become especially dangerous - the westernmost in the archipelago. It is located in the place of a powerful tectonic fault, the so-called "Pacific Ring of Fire".

The plate that forms the bottom of the Indian Ocean "squeezes" under the Asian plate here as fast as a human fingernail grows. The accumulated tension is released from time to time in the form of tremors.

Medan is the largest city on the island and the third most populous in the country. As a result of two strong earthquakes in 2013, more than 300 local residents were seriously affected, and about 4,000 houses were damaged.

Tehran, Iran

Scientists have been predicting a catastrophic earthquake in Iran for a long time - the whole country is located in one of the most seismically active zones in the world. For this reason, the capital Tehran, where more than 8 million people live, was repeatedly planned to be moved.

The city is located on the territory of several seismic faults. Earthquakes of 7 points would destroy 90% of Tehran, whose buildings are not designed for such violence of the elements. In 2003, another Iranian city of Bam was turned into ruins by a 6.8 magnitude earthquake.

Today, Tehran is familiar to tourists as the largest Asian metropolis with many rich museums and majestic palaces. The climate allows you to visit it at any time of the year, which is not typical for all Iranian cities.

Chengdu, China

Chengdu is an ancient city, the center of the southwestern Chinese province of Sichuan. Here they enjoy a comfortable climate, see numerous sights, and become imbued with the original culture of China. From here they get along tourist routes to the gorges of the Yangtze River, as well as to Jiuzhaigou, Huanglong and.

Recent events have reduced the number of visitors to these parts. In 2013, the province experienced a powerful earthquake of magnitude 7, when more than 2 million people were affected and about 186,000 houses were damaged.

Residents of Chengdu annually feel the effect of thousands of tremors of varying strength. In recent years, the western part of China has become especially dangerous in terms of seismic activity of the earth.

What to do in case of an earthquake

• If an earthquake caught you outside, stay away from the eaves and walls of buildings that could fall. Stay away from dams, river valleys and beaches.
• If an earthquake caught you in a hotel, open the doors so that you can safely leave the building after the first series of aftershocks.
• During an earthquake, you can not run out into the street. Many deaths are caused by falling debris from buildings.
• In case of a possible earthquake, it is worth preparing a backpack with everything you need for a few days in advance. A first aid kit, drinking water, canned food, crackers, warm clothes, and washing accessories should be at hand.
• As a rule, in countries where earthquakes are frequent, all local cellular operators have a system for alerting customers about an approaching disaster. On vacation, be careful, watch the reaction of the local population.
• After the first push, there may be a lull. Therefore, all actions after it should be thoughtful and cautious.