In the depths of the Earth's interior, certain processes are constantly taking place, and they equally affect both land areas and part of the crust under the bottom of the world's oceans.


Tectonic plates shift, layers collide, causing vibrations, and underground volcanoes erupt. Underwater earthquakes do not go unnoticed: these phenomena cause huge waves, often reaching the continents. These waves are called tsunami– translated from Japanese the term means "a giant wave that came into the harbor" .

The column of water that moves as a result of vibrations of the seabed is practically harmless far from land. But the closer to the shore the wave moves, the more power it gains, and the higher its crest becomes. The lower layers of water, passing along the bottom and encountering resistance, further increase the energy of the upper layers.

A tsunami can move at speeds of up to 800 kilometers per hour, and the wave height is often ten, twenty, or even thirty meters. This mass of water, falling onto the shore, destroys everything in its path, throwing debris many kilometers inland. The danger of a tsunami also lies in the fact that it is not a single wave: there can be up to a dozen waves in total, with the third and fourth being the most dangerous.

But a tsunami may not look like waves, but like a series of rapidly changing strong ebbs and flows, which carries no less danger.

Causes of tsunamis

Up to 7% of all tsunamis are caused by landslides, when huge blocks of earth, rock or ice fall into the water. In 1958, in Alaska, such a landslide led to the formation of a wave 524 meters high.


Underwater landslides in river deltas are also dangerous. Landslide tsunamis regularly occur in Indonesia and result in twenty-meter tsunamis. Another 5% of cases occur due to underwater volcanic eruptions. Human activity can also lead to a tsunami, for example, testing of deep weapons.

Up to 85% of all cases where tsunamis were recorded are associated with. At the same time, the ocean bottom shifts vertically, and the surface of the water begins to move, trying to return to its previous level. Tsunamis are mainly generated by earthquakes with sources located close to the surface.

During earthquakes, surface waves called local tsunamis emanate from the site of vertical shear. The height of such waves can reach thirty meters. At the same time, underwater waves diverge from the epicenter, passing through the entire thickness of the water, from the bottom to the surface, and moving at a speed of 600 to 800 kilometers per hour.

As the depth of the ocean decreases, the energy of such a wave is concentrated closer to the surface, resulting in such distant tsunamis hitting the shore. A remote tsunami can cross from end to end of the Pacific Ocean in a day, reaching from the coast of Chile to the islands of Japan.

Moreover, it is almost impossible to notice such a wave in the ocean - with a length of 200-300 kilometers, it has a height of up to a meter. This is the main insidiousness of the tsunami.

How to understand that a tsunami is approaching?

In any case, an earthquake can become a harbinger of a tsunami for coastal regions. Sometimes, before the arrival of a large wave off the coast, there is a sharp ebb of tide and exposure of a wide strip of the seabed, which can last from several minutes to half an hour.


Animals show increased anxiety before the arrival of a tsunami, trying to climb to elevated places.

What to do if you find yourself in a tsunami zone?

The most dangerous areas from this point of view are the coast, harbors, bays with a height of no more than 15-30 meters above sea level. If you are in such an area and expect that a tsunami will soon come ashore, keep documents, a minimum supply of food and things collected in case of emergency evacuation.

It is worth looking in advance for hills and tall buildings where you could climb to avoid danger. It is worth remembering that a distance of two to three kilometers from the shore can be considered relatively safe. Since it is impossible to predict either the number or frequency of waves, it is better not to approach the coast for two to three hours after the last wave arrived.

Knowing these simple rules could have saved many lives during the 2004 Southeast Asian tsunami. Then dozens of people wandered around the shallows after a sudden low tide, collecting shells and fish. Hundreds more returned to shore after the first wave of the tsunami to check if their homes were safe, unaware that the first wave would be followed by others.

The worst tsunamis of our century

In 2004, trouble came to Southeast Asia. At the end of December, an earthquake with a magnitude of more than 9 occurred in the Indian Ocean. The tsunami passed through Indonesia, Sri Lanka, Thailand and the coast of Africa. More than 235 thousand people died. The situation was aggravated by the fact that at this time of year thousands of tourists come to Asian countries to celebrate the New Year on the warm sea. The tsunami destroyed a lot of resort regions in several countries.


In March 2011, a powerful earthquake occurred in Japan, causing a forty-meter tsunami. The disaster brought the death of nearly 16 thousand people, and more than seven thousand are still considered missing. A tsunami and earthquake destroyed the Fukushima-1 nuclear power plant, and people are still eliminating the consequences of this accident.

On the pages of our website we have already talked about one of the most dangerous natural phenomena - earthquakes: .

These vibrations of the earth's crust often give rise to tsunamis, which mercilessly destroy buildings, roads, and piers, leading to the death of people and animals.

Let's take a closer look at what a tsunami is, what are the causes of its occurrence and the consequences it causes.

What is a tsunami

Tsunamis are high, long waves generated by a powerful impact on the entire thickness of ocean or sea water. The term “tsunami” itself is of Japanese origin. Its literal translation is “a big wave in the harbor” and this is not in vain, since in all their power they manifest themselves precisely on the coast.

Tsunamis are generated by a sharp vertical displacement of the lithospheric plates that make up the earth's crust. These gigantic vibrations vibrate the entire thickness of the water, creating a series of alternating ridges and depressions on its surface. Moreover in the open ocean these waves are quite harmless. Their height does not exceed one meter, since the bulk of the oscillating water extends below its surface. The distance between the ridges (wavelength) reaches hundreds of kilometers. The speed of their spread, depending on the depth, ranges from several hundred kilometers to 1000 km/h.

Approaching the shore, the speed and length of the wave begins to decrease. Due to braking in shallow water, each subsequent wave catches up with the previous one, transferring its energy to it and increasing its amplitude.

Sometimes their height reaches 40–50 meters. Such a huge mass of water, hitting the shore, completely devastates the coastal zone in a matter of seconds. The extent of the destruction area deep into the territory in some cases can reach 10 km!

Causes of tsunami

The connection between tsunamis and earthquakes is obvious. But do vibrations in the earth's crust always generate tsunamis? No, tsunami are generated only by underwater earthquakes with a shallow source and magnitude greater than 7. They account for about 85% of all tsunami waves.

Other reasons include:

  • Landslides. Often a whole chain of natural disasters can be traced - a shift of lithospheric plates leads to an earthquake, which generates a landslide that generates a tsunami. This is precisely the picture that can be seen in Indonesia, where landslide tsunamis occur quite often.
  • Volcanic eruptions cause up to 5% of all tsunamis. At the same time, gigantic masses of earth and stone, soaring into the sky, then plunge into the water. A huge mass of water is shifting. Ocean waters rush into the resulting funnel. This dislocation generates a tsunami wave. An example of a disaster of absolutely terrifying proportions is the tsunami from the Karatau volcano in 1883 (also in Indonesia). Then 30-meter waves led to the death of about 300 cities and villages on neighboring islands, as well as 500 sea vessels.

  • Despite the presence of our planet’s atmosphere, which protects it from meteorites, the largest “guests” from the universe overcome its thickness. When approaching the Earth, their speed can reach tens of kilometers per second. If such meteorite has a large enough mass and falls into the ocean, it will inevitably cause a tsunami.

  • Technological progress has brought not only comfort to our lives, but has also become a source of additional danger. Conducted underground nuclear weapons testing, this is another reason for the occurrence of tsunami waves. Realizing this, the powers possessing such weapons entered into a treaty prohibiting their testing in the atmosphere, space and water.

Who studies this phenomenon and how?

The destructive effect of the tsunami and its consequences are so enormous that humanity has become the problem is to find effective protection against this disaster.

The monstrous masses of water rolling onto the shore cannot be stopped by any artificial protective structures. The most effective defense in such a situation can only be the timely evacuation of people from the danger zone. For this a sufficiently long-term forecast of the upcoming disaster is necessary. Seismologists do this in collaboration with scientists from other specialties (physicists, mathematicians, etc.). Research methods include:

  • data from seismographs recording tremors;
  • information provided by sensors carried out into the open ocean;
  • remote measurement of tsunamis from outer space using special satellites;

  • development of models for the occurrence and propagation of tsunamis under various conditions.
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There are all sorts of elements on Earth: tornadoes, tsunamis, earthquakes, volcanic eruptions, avalanches, floods, fires, and so on. Many of them are destructive. Let's talk more about tsunamis. Many people know first-hand what it is. “Big wave in the harbor” is how the word “tsunami” is translated. We are talking about marine gravity waves that arise as a result of earthquakes (underwater, coastal) or the displacement of individual sections of the seabed.

Many people really know the destructive power of tsunamis. People are very afraid of this unbridled phenomenon. And this fear is passed on from generation to generation. Sometimes tsunamis are even called “rogue waves” because they have already claimed millions of lives.

A tsunami has the following characteristics:< ul >

  • wave height reaches 50 meters and above;
  • its propagation speed is 50-1000 km/h;
  • the number of waves arriving on the shore ranges from 5 to 25;
  • the distance between waves can reach 10-100 or more kilometers.
  • Do not confuse tsunamis with ship and storm waves. In the first case, the entire thickness of the wave moves, in the second - only the surface layer.

Tsunami: what is it - causes and signs

Scientists have been studying the nature of such a phenomenon as a tsunami for decades. Among the reasons that cause it are:

  • underwater landslides;
  • falling into the ocean or sea of ​​meteorites, comets or other celestial bodies;
  • volcanic eruptions (underwater);
  • underwater earthquakes;
  • tropical cyclones, typhoons;
  • excessively strong wind;
  • testing of military weapons.

As a result of any of the above reasons occurring on the seabed, a force is released that creates lightning-fast movement of water. Most often, a tsunami is caused by underwater earthquakes.

Scientists can guess what the consequences will be after such a disaster. But it is extremely difficult for people to survive this, and more often it is impossible. It's no wonder why all the dinosaurs died at one time.

Is it possible to know in advance that a tsunami is coming? Of course, scientists have identified a number of signs indicating that a tsunami is about to happen. The first sign of a tsunami is an earthquake. Therefore, when you feel the first intense tremors, you can understand that the wave will be strong. The second sign is a sharp ebb. The further the water goes deeper into the ocean or sea, the higher the waves will be.

Tsunami: myths and truth

People live and do not know that not all the stories about the tsunami that circulate among people are true.
Myths:

  1. Tsunamis can only occur in warm seas. This is wrong. They happen everywhere. It's just that tsunamis most often occur in the Pacific Ocean.
  2. The power of a tsunami depends on how far the water has moved away from the shore before the disaster. In reality, it is the wavelength that depends on the water flow, not its power. And the coast does not always become shallow before a tsunami. Sometimes, on the contrary, the water is before the tsunami.
  3. A tsunami is always accompanied by a large wave. No, a tsunami is not just a wall of water that hits the shore. In some cases, such a wall may not exist.
  4. The arrival of a tsunami is always invisible. Yes, the elements do not clearly warn of their approach. But attentive scientists always notice the approach of a tsunami.
  5. The largest is the first wave of the tsunami. This is not true again. The waves reach the coast after a certain period of time (from several minutes to an hour). And it is the waves following the first that often turn out to be more destructive, since they “fall” onto the wet shore when the resistance has already been reduced.

The truth is that animals always sense when a tsunami is coming. They try to leave the dangerous area in advance. Therefore, after a tsunami, you may not find animal corpses at all. At the same time, fish try to hide in corals. Perhaps it makes sense to listen to the “call” of pets for everyone who lives in seismic zones?!

How to escape from a tsunami?

The only thing that can save life in such a catastrophic situation is to flee inland. People who find themselves hostage to the elements must leave as soon as possible and run away from the coastline. In this case, you should lay your route away from river beds, because tsunami waves can reach there very quickly. Ideally, you should climb a mountain to a height of more than thirty meters. Those who are caught by the elements at sea should sail on a ship further out to sea, since sailing to the shore is simply pointless - certain death awaits there.
By following the recommendations, remaining calm and vigilant, and having good preparation, you can always save yourself from such a destructive element. But the best advice: if you are very afraid of dying during a tsunami, leave seismic areas. As you know, tsunamis are frequent guests of the coast, the Pacific Ocean (about 80% of all active volcanoes on Earth are concentrated here), Sakhalin Island, the Maldives, the coast of Australia, Japan, India, Peru, Thailand, Madagascar.

Tsunami(Japanese 津波 IPA: where 津 - “port, bay”, 波 - “wave”). Translated from Japanese it means “big wave in the harbor” or simply “wave in the harbor”. Tsunamis are long waves generated by a powerful impact on the entire thickness of water in the ocean or other body of water.
They have spatial scales from several hundred meters to several hundred kilometers. Tsunami wave propagation speed (c) described by the formula Lagrange:

с=√gh,

Where h- depth of the ocean;

g- free fall acceleration.

Causes of tsunamis.

Tsunamis are not always generated by any one phenomenon; they can be caused by a combination of them. For example, an earthquake and a landslide, a volcanic eruption accompanied by an earthquake and a landslide, and so on.

Most tsunamis are caused by underwater earthquakes(today it is believed that this is the reason that accounts for about 85 % all tsunamis), during which a sharp displacement (raising or lowering) of a section of the seabed occurs. Not every underwater earthquake is accompanied by a tsunami. The tsunami wave that generates is usually an earthquake with a shallow source. The only problem is the lack of ability to 100% recognize such earthquakes, because warning services focus only on magnitude indicators.

Second reason are landslides(near 7% all tsunamis). Once a landslide occurs, it immediately generates a wave. An earthquake can cause a landslide. Underwater landslides most often occur in river deltas.

The third reason are volcanic eruptions(near 5% all tsunamis). Large underwater eruptions have the same effect as earthquakes. A classic example is the tsunami generated after the Krakatoa eruption in 1883. Huge tsunamis from the Krakatoa volcano were observed in harbors around the world and destroyed a total of 5,000 ships and, as a result, killed about 36,000 people.

In the age of the use of atomic energy, a person has in his hands a means to independently cause shocks, previously available only to nature. Therefore, it should be understood that fourth reason is human activity. Here it should be remembered that in 1946, the United States carried out an underwater atomic explosion with a TNT equivalent of 20 thousand tons in a sea lagoon 60 m deep. The resulting wave at a distance of 300 m from the explosion rose to a height of 28.6 m, and 6.5 km from the epicenter still reached 1.8 m. And, although international treaties currently prohibit underwater testing of atomic weapons, but, as practice shows, such agreements are formal in nature and serve only to personally reassure citizens of adjacent territories in their imaginary safety and comfort.

A small, but not so safe percentage falls on meteorological reasons(such as the fall of a large celestial body) and other potential causes, described in scientific circles as “unknown” (but very dangerous). Meteorological reasons today are a rather poorly understood phenomenon. They are recorded mainly in the Pacific, Atlantic and Indian oceans.

Features of tsunami propagation

Far from the coast, the height of a tsunami is no more than 2-2.5 m, and its length can reach several hundred kilometers. These tsunamis are very gentle and almost imperceptible to ships passing over them.

The speed of a tsunami depends entirely on its depth and can reach speeds of up to 800 km/h. The most interesting thing is that in the open ocean, tsunamis are invisible, although they move at a speed of 700-800 km/h, but when approaching the shore, the speed noticeably decreases with a significant increase in the height of the approaching wave.

If a tsunami moves towards the shore, then its height, reaching shallow water, begins to increase to 20-30 m, and in some cases can reach 30-60 m. Near the shore itself, the tsunami becomes steeper and higher, reaching its peak point along the entire path of its journey.

This leads to enormous destruction and numerous casualties. Examples of this phenomenon were the coasts of Thailand, Indonesia, India and Sri Lanka during the tsunami of December 26, 2004. in the Indian Ocean, as well as the northeastern part of Japan on March 11, 2011 (the magnitude of the earthquake that generated the tsunami was 9.0 points).

From the point of view of the development of science today, we can say that the height of the tsunami on the coast and the features of movement inland depend on the size of the initial disturbance of sea level, bottom slopes, and the configuration of the coastline of the terrain.

Tsunamis are most dangerous in narrowing bays and straits, as well as in the mouth areas of rivers flowing into the sea. Tsunamis penetrate furthest along river valleys. Examples of such areas are: the Second Kuril Strait, Tuharka Bay on the island of Paramushir, Crab Bay on the island of Shikotan, the mouth of the Kamchatka River and others.

The tsunami threat at any point during the day can rise or fall sharply depending on fluctuations in the tidal level.

The very first harbingers are animals and birds, which, sensing danger, leave their habitats in the period from several hours to several days, or even weeks before the impending disaster. It’s as if our Mother Earth herself is taking care of warning living things about danger through various energy waves captured by animals and birds.

For example, residents of earthquake-prone Japan have been determining the danger of earthquakes for hundreds of years by the behavior of aquarium fish. Thus, on the eve of a tsunami, Japanese catfish literally try to jump out of the aquarium and constantly rush from wall to wall. Repeated observations, including those carried out by scientists from the experimental oceanological laboratory of the Russian Hydrometeorological University, also confirmed that ocean fish also leave coastal waters several hours before the tsunami. Studies have shown that stingrays, carp fish, catfish and crayfish are especially sensitive to changes in electromagnetic fields before natural disasters.

It is no coincidence that biochemist H. Tributsch notes that, shortly before the onset of earthquakes and the subsequent occurrence of tsunamis, a powerful stream of charged particles or ions rushes from the soil surface into the atmosphere, which saturate the air with electricity to the limit, causing increased excitability, nausea, and headaches in people. It is these electrostatic fields that force animals to leave dangerous areas. And a group of German researchers from Tübingen, led by Professor W. Ernst, also found a change in the color of leaves of flowers, shrubs and trees several weeks before earthquakes. Such changes can be recorded using space satellites, which will allow people to be warned about danger in advance.

Signs of a tsunami may also include:

  1. A sudden rapid withdrawal of water from the shore over a considerable distance and drying out of the bottom.
  2. The occurrence of an earthquake. In tsunami-prone regions, there is a rule that if an earthquake is felt, it is better to move further from the coast and at the same time climb a hill, in order to thus prepare in advance for the arrival of the wave.
  3. During a storm, only the surface layer of water moves. During a tsunami - the entire thickness of water, from the bottom to the surface.
  4. A tsunami, as a rule, generates not one, but several waves. The first wave, not necessarily the largest, "wets the surface", reducing resistance for subsequent waves.
  5. The speed of tsunami waves, even near the shore, exceeds the speed of wind waves. The kinetic energy of tsunami waves is also thousands of times greater.

Consequences of the tsunami.

The consequences of the tsunami are huge human casualties. Human life alone is a priceless gift and gift.
As the first of the seven foundations of AllatRa states, the highest value in this world is human life. And it is very important to protect the life of any person as your own, because although it is fleeting, it gives everyone a chance to increase their main value - their inner spiritual wealth, the only thing that opens the Personality to true spiritual immortality.

The worst consequence of a tsunami is the loss of at least one priceless human life.


But, in addition to the loss of life, tsunamis also cause flooding of large coastal areas, salinization and erosion of soils, destruction of buildings and structures, and damage to ships moored near the coast. A tsunami deals a huge blow to the economy of the country in which such a disaster occurs. The economic losses from the tsunami are colossal and amount to truly astronomical sums of money allocated to eliminate the consequences and restore the destroyed infrastructure of the region.

An example of this is an event in Japan. According to experts, a year after the earthquake and the resulting tsunami, the damage to Japan is estimated at 210.00 billion US dollars. This tsunami not only became the most expensive natural disaster in history. But it also destroyed 128,582 and partially destroyed 243,914 buildings. About 320,000 people lost their homes and 15,848 lost their lives. Another 3,305 people are considered missing.

What to do if a tsunami occurs?

We must make sure that documents, the necessary minimum of things and products are always at hand.

You should discuss with family members a meeting place after a disaster, consider evacuation routes from a dangerous coastal area, or identify places for rescue if evacuation is not possible. These may be local hills or high capital buildings. You need to move to them by the shortest route, avoiding low-lying places. A distance of 2-3 km is considered safe. from the shore.

It is important to understand that when tsunami warning signs, tremors are observed, or local tsunami warnings are issued, the time to rescue can be measured in minutes. Therefore, it is necessary to act instantly, remaining collected and as calm as possible.

The occurrence of distant tsunamis is detected by warning systems and the forecast is communicated by radio and television. Such messages are preceded by the sound of sirens.

The number, height of waves, as well as the interval between them is impossible to predict. Therefore, after each wave it is dangerous to approach the shore for 2-3 hours. It is advisable to use the gap between waves to find the safest place.

Any earthquake felt on the seashore should be considered a tsunami hazard.

You cannot go close to the shore to watch the tsunami. It is believed that if you see a wave and are in a low-lying place, it is too late to save yourself.

Compliance with these simple rules of behavior and knowledge of tsunami precursors could reduce the number of victims of the Indian Ocean tsunami in 2004. Indeed, according to eyewitnesses (this can also be seen in the recorded videos), many people used such a harbinger of a tsunami as the low tide before the arrival of the wave to walk along the seabed and collect sea animals, shells, as well as various things left after the rapid “leaving” of the water during low tide

With correct behavior, the number of saved people could reach tens of thousands.

It is necessary to pay attention to the development of science in the field of observation of animals, birds, fish and the entire surrounding world, so that, together with these harbingers of upcoming changes, we are fully armed and informed as much as possible about the impending future.
It is important to understand that in order to reduce damage from the consequences of a tsunami, it is necessary to take great responsibility for construction, which should be carried out outside the tsunami impact zone. If this is not possible, build buildings so that they absorb impacts on their short side, and/or place them on strong columns. In this case, the wave will freely pass under the building without causing damage to it.

If there is a threat of a tsunami, ships moored near the coast must be taken out to the open sea.

You should pay attention and your understanding that there are no state territories on planet Earth.

It is people themselves, by desire and choice, who share one indivisible planet, one whole and the only one, dividing it in all possible ways - whatever their imagination and greed is enough for. All this division is just an appearance for the mind and an outlet for the ego, especially the imaginary owners of artificially created territories in distant and not so distant history. We are all Earthlings. We are all inhabitants of the Earth. And it doesn’t really matter what complexion each of us has, where we live or what we believe.

It is important to support each other, lend a helping hand to your neighbor, and take care of the people around you in every possible way. And then no disaster will become an obstacle in the life of every person, but will only be a temporary task, overcoming which with joint efforts will be easy and least painful for the people “affected” by the disaster.

The tsunami phenomenon itself is as old as the Ocean. Eyewitness stories about terrible waves, passed from mouth to mouth, became legends over time, and about 2000-2500 years ago written evidence appeared. According to one of them, Atlantis perished. Researchers also name a tsunami among the likely reasons for the disappearance of the island.

The time of this grandiose event dates back to ancient times - 2500 years ago. It is clear that there could be no talk of any scientific examination of the phenomenon at that time. The study of tsunamis became possible only after the emergence and development of seismology, since a tsunami, as a rule, is a consequence of an earthquake, in turn, the birth of the science of seismology can be considered the time of invention (the beginning of the current century) by the Russian scientist academician B. B. Golitsyn of an electrodynamic seismograph - an instrument with the help of which the epicenter of an earthquake is determined relatively accurately and simply.

Currently, different views are expressed on the causes of tsunamis. Along with the main cause - earthquakes, these include surges of water into bays caused by typhoons, storms, and strong tides. This appears to be explained by the origin of the word “tsunami” (translated from Japanese as “harbour wave”).

There are also different views on the mechanism of formation of a tsunami source excited by earthquakes. In particular, it is assumed that the earthquake itself does not excite a tsunami, but serves only as a trigger mechanism. The reason is turbidity (suspension, turbidite) flows of sedimentary matter, which has thixotropic properties (under certain conditions, capable of liquefaction) and accumulates in the canyons of tsunamigenic zones and areas. During earthquakes of even small magnitude, this substance receives a kind of impetus to rapid liquefaction and movement and creates the preconditions for the occurrence of a tsunami source.

Without entering into a discussion about the correctness of the views expressed, let us turn to the most common definition of tsunamis and the causes that give rise to them. By “tsunami” we mean long-period marine gravity waves that suddenly arise in the seas and oceans precisely as a result of earthquakes, the sources of which are located under the bottom of the seas and oceans. Tsunamis can also arise from explosions of underwater volcanoes, underwater and coastal landslides and landslides, which in turn form as a result of earthquakes.

These waves have a high propagation speed and enormous kinetic energy, which contributes to their deep penetration onto land. When approaching the shore, they become deformed and, rolling onto the shore, sometimes cause enormous destruction. It should be noted that only tsunamis generated by high-energy earthquakes with a magnitude approximately equal to or greater than 8.0 have significant destructive power.

Recent preliminary studies show that tsunamis can be caused by earthquakes of significantly lower magnitude (for example, M>5.0). But they most often manifest themselves in the form of minor flooding, which can only be detected with the help of appropriate instruments. Tsunami sources are usually confined to the epicentral regions of earthquakes.

It is known that the largest number of earthquakes occurs on the Pacific coast. It is natural to assume that tsunamis most often occur in the Pacific Ocean. Approximate calculations show the following distribution (in%) of tsunamis in various seas and oceans:

Pacific Ocean (mostly peripheral) 75

Atlantic Ocean 9

Indian Ocean 3

Mediterranean Sea 12

Other seas 1

In the Soviet Union, essentially only the Far Eastern coasts are exposed to tsunamis: Kamchatka, the Kuril and Commander Islands and, partially, Sakhalin.

So, as a result of what processes do tsunamis occur? Observations show that this is mainly: a) a sudden displacement of a section of the surface of the sea or ocean in the vertical direction (or close to vertical) due to a similar downward or upward displacement of the corresponding section of the seabed; b) a sharp shift of water in the horizontal (or close to it) direction due to a similar displacement of large blocks of the earth’s crust with steep slopes near deep-sea depressions; c) above-water or underwater collapses and landslides; d) explosions or large eruptions of underwater volcanoes; e) bottom vibration, etc.

It should be borne in mind that a tsunami occurs only in the case of a rapid, almost instantaneous completion of these processes. When powerful tsunamis occur, we can talk about at least four conditions that favor them: 1) the source of the earthquake is located under the bottom of the sea, ocean (it happens, although rarely, that the sources of an earthquake and a tsunami do not coincide) or in comparative proximity to those large blocks of the earth’s crust, which, moving as a result of an earthquake in a horizontal direction towards the ocean, come into direct contact with large water columns; 2) above the epicentral region of the earthquake there is a layer of water of significant thickness; 3) the depth of the earthquake source is small (10-60 km); 4) the earthquake must be of great strength (or if we are talking about a landslide or collapse, then the mass of rocks involved in the formation of the tsunami must have a sufficiently large volume).

As a rule, tsunamis with foci in deep-sea zones have the greatest destructive power.

In the open ocean, tsunami waves are low (in the case of the strongest earthquakes, they presumably do not exceed 2-3 m), have a significant (sometimes reaching 200-300 km) wavelength and a propagation speed commensurate with the speed of a modern passenger jet.

The speed of the wave is determined by the Lagrange formula: v = (square root)gH, where g is the acceleration of gravity and H is the depth of the pool at the place where the speed is determined.

When approaching the shore, depending on the coastal bottom topography and the configuration of the coastline, a tsunami can “grow” from 1-2 m in height in the open ocean to several tens of meters on the shore. But, perhaps, the main reason for the increase in wave height is the decrease in ocean depth. The latter can be calculated using the Airy-Green formula:

where hm is the height of the wave in shallow water with a depth of Hm; - wave height at depth Нp.

The transformation and growth of the wave begins to noticeably manifest itself at the boundary of the continental shallows (depth 200 m or less) and occurs most intensively from a depth of 10-15 m. Once in the shallow coastal zone, the wave is deformed - its height increases with a simultaneous increase in the steepness of the leading front. As it approaches the shore, it begins to capsize, creating a foaming, seething, high-height water flow, which causes destruction on the shore.

The destructive power of tsunami waves depends on the intensity of the earthquakes that generated them, the distance from the point of origin to the shore, the length of the tsunami source and the initial height of the wave, as well as on the features of the bottom topography along the path of wave propagation and the configuration of the coastline.

With very steep bottom slopes and straight shores, as well as in areas with fairly high shores, the tsunami does not grow strongly and does not cause any significant destruction. A particular danger is posed by narrowing bays and straits with decreasing depths, in which there is a significant increase in height, and therefore the destructive effect of waves. Moreover, in the case of a low-lying coast, the wave covers large areas of land, sweeping away everything in its path. The extreme danger is posed by river mouths, through which a tsunami can penetrate deep into the territory at a distance of several kilometers. Wave height decreases only in closed, expanding bays with a narrow entrance.

Most people have a good understanding of the nature and parameters of ordinary wind waves and a very poor understanding of tsunamis. For comparison, we present a table of some characteristic parameters of wind waves and tsunami waves (maximum values).

From the table 4 shows, in particular, that in the open sea the height of tsunami waves does not exceed 3 m. Having at the same time a very long length, they become safe for any watercraft located in the ocean at a considerable distance from the coast.

An extremely interesting, somewhat unique case of an extremely high wave should be cited. On July 9, 1958, as a result of an earthquake in Alaska, a mass of ice and earth rocks with a volume of about 300 million m3 of the Lituya glacier from a height of close to 900 m fell into the narrow and long Lituya Bay, causing a colossal wave splash on the opposite side of the bay, reaching some sections of the coast are almost 600 meters high. At this time, there were three small fishing vessels in the bay. “Despite the fact that the disaster took place nine kilometers from the ship’s anchorage, everything looked terrible. Before the eyes of the shocked people, a huge wave rose up and swallowed the foot of the northern mountain. After that, she swept across the bay, tearing trees from the mountainsides, destroying the recently abandoned climbers' camp; falling like a mountain of water onto Cenotaph Island, it swallowed up an old hut... and finally rolled over the highest point of the island, which rose 50 m above sea level.

The wave spun Ulrich's ship, which, having lost control, rushed at the speed of a galloping horse towards the ships of Swanson and Wagner, still at anchor. To the horror of the people, the wave broke the anchor chains and dragged both ships like splinters, forcing them to overcome the most incredible journey that has ever befallen a fishing boat. According to Swansop, below the ship they saw the tops of 12-meter trees and rocks the size of houses. The wave literally threw people across the island into the open sea.”

Cases of this kind are very rare and cannot be considered as a standard. However, history knows many examples of tsunamis that are inferior in strength to the one described, but no less severe in their consequences.

Earthquake near the eastern coast of Kamchatka. The height of the excited tsunami waves reached 25-30 m. There was very great destruction in almost all coastal villages of eastern Kamchatka. Due to the weak population at that time, there were few casualties among the population.

An earthquake and tsunami (the epicenter southwest of Lisbon, in the Atlantic Ocean) destroyed and washed away Lisbon. 15 thousand out of 20 thousand buildings were destroyed. About 50 thousand people died. The wave height reached 25-30 m.

Explosion of the Krakatau volcano (Sunda Strait, between the islands of Java and Sumatra). As a result of the explosion, a series of very large tsunami waves arose, not only sweeping along the shores of the Indian and Pacific oceans, but also reaching the Atlantic, reaching the coasts of France and Panama. Off the coast of Java and Sumatra, the wave height reached 30-40 m. The Dutch ship was thrown onto land by a wave and ended up 4 km from the coast at an altitude of 10 m above sea level. Colossal destruction on the islands: residential villages were washed away from the low-lying shores of western Java and southern Sumatra, coastal forests and crops were destroyed. About 36 thousand human casualties.

Sanriku earthquake (general name for the Pacific coast of Aomori, Iwate, Miyagi prefectures). The epicenter is 240 km from the coast of Japan. The tsunami on the shore in some places reached a height of 30 m. About 11 thousand residential premises and public buildings were washed away. 27 thousand people died.

Strong earthquake in Japan. Waves more than 30 m high hit the Sanriku coast. The city of Kamaishi was destroyed, where 1,200 houses were washed away. A large number of trees were blown down. About 4,000 people died. A lot of material damage was caused.

The epicenter of the earthquake is near Unimak Island (Aleutian Islands) in the Aleutian Trench. Despite the great distance of the Hawaiian Islands from the tsunami source (3700 km), even there waves with a height of 11 m (Oahu Island) and 16 m (Hawaii Island) were recorded. The tsunami reached the shores of Alaska, North and South America. The largest wave was observed on Unimak Island: the lighthouse, which stood at Cape Scotch Cap, 34 m above sea level, was washed away, and all its staff (5 people) died. In total, about 200 people became victims of this tsunami. Losses are estimated at $25 million.

This tsunami is the strongest for the Far Eastern coast of the USSR, especially in its consequences, so it should be given more attention, especially since it has not been forgotten by the inhabitants of the Far East to this day. Materials on this event were published in the Bulletin of the Council on Seismology of the USSR Academy of Sciences (1958, No. 4). On the night of November 4-5, 1952, at about 4 o'clock. local time, residents of Severo-Kurilsk were awakened by a magnitude 7 earthquake.

After 45 min. after the earthquake began, a loud roar was heard from the ocean, and within a few seconds a huge wave hit the city, moving at high speed and having its greatest height in the central part of the city, where it rolled along the river valley.

A few minutes later the wave rushed out to sea, taking with it everything destroyed. The retreat of the first wave was so intense that the bottom of the strait was exposed for several hundred meters. There was a lull.

After 15-20 minutes. A second, even larger wave, reaching 10 meters in height, hit the city. It caused particularly severe destruction, washing away all the buildings in its path; only the cement foundations of the houses remained.

The wave that passed through the city reached the slopes of the surrounding mountains, after which it began to roll back into the basin located closer to the city center. A huge whirlpool formed here, in which all kinds of fragments of buildings and small ships rotated at high speed. Rolling back, the wave hit the coastal rampart in front of the port area from the rear and, bypassing the mountain, broke through into the Kuril Strait. The section of the coastal rampart and the mountain became an island for a few minutes. On the bridge between this island and the mountain, the wave piled up a pile of logs, boxes, etc., and even brought two houses from the city.

A few minutes after the second wave, a weaker, third wave arrived, which washed a lot of debris ashore. All this was scattered throughout the city and along the banks of the strait. At 9 o'clock In the morning, strong fluctuations in sea level were observed, which, weakening, were repeated throughout the day on November 5.

In the strait, during the passage of the tide, the formation of whirlpools and ripples occurred - standing waves and vertical splashes formed as a result of the collision of currents coming from the Pacific Ocean and the Sea of ​​​​Okhotsk towards each other.

This is how events developed during the tsunami in Severo-Kurilsk. It covered an almost 700-kilometer zone of the Far Eastern coast. The highest waves were recorded in Piratkova (10-15 m) and Olga (10-13 m) bays in Kamchatka.

Near Valdivia (coast of Chile), a catastrophic earthquake generated a tsunami that swept the coasts of all Pacific countries. It caused enormous material damage to most states. There were human casualties. The height of the waves off the coast of Chile reached 20 m. The number of victims in Chile alone was estimated at 2,000 people. 50 thousand houses turned into ruins. The total damage amounted to several hundred million dollars.

As a result of a very strong earthquake in Prince William Sound (Alaska), a tsunami was recorded along the coast of the entire Pacific basin. The height of the waves in some areas reached 10 m. More than 120 people died from the tsunami in different places. The total damage from the earthquake and tsunami amounted to several hundred million dollars.

Science has revealed many great “secrets” of nature and put them at the service of man: electricity and magnetism, atomic energy and laser radiation, the laws of motion of cosmic bodies and the genetic code of a living cell, etc. However, much still needs to be known, discovered, and invented. Apparently, many decades will pass before a person learns to predict some formidable natural phenomena, and then control them.

What can be done in the near future to protect people and various economic facilities from the natural disasters described above? Since a tsunami is a secondary phenomenon that depends on an earthquake, this issue should be considered in its entirety. There are cases when even the strongest earthquake poses absolutely no danger to a particular area (the source of the earthquake is located many thousands of kilometers away), but the resulting wave, covering vast distances, can be the culprit of great destruction.

In our opinion, there are three main ways to avoid the misfortunes described. This includes resettlement from seismically active and tsunami-prone areas, forecasting earthquakes and tsunamis, earthquake-resistant construction taking into account pre-conducted zoning. Let's see how feasible this is.

The first method is rejected by the residents themselves, because for thousands of years they have settled their area, developed landscaping, developed natural resources, and the prospect of losing all this seems to people much more depressing than the threat of facing a formidable element.

The second method - earthquake forecasting - is still in the research stage. Moreover, it must be considered in two aspects: long-term and short-term prediction of events. Long-term forecasting of earthquakes (and therefore tsunamis) is a matter of the future. Short-term - it is already producing positive results, although the final solution to the issue is still quite far away. The situation is somewhat better with the short-term tsunami forecast, which will be discussed below. Here we will only mention that protecting the population from the possible occurrence of a tsunami at present essentially comes down to the population leaving areas where flooding is expected to higher places, but it is not possible to save buildings from destruction.

There remains a third method - earthquake-resistant construction; This is perhaps the main thing that can minimize the results of possible disasters. But, since the construction of structures with an appropriate safety margin is expensive work, it is necessary that it be preceded by clear microseismic zoning, so that, on the one hand, not to overestimate the seismicity of the specific area where the construction will be carried out, and on the other hand, not to underestimate it, since this is related with the safety of the population.

Of course, all three methods of protecting the population from seismic hazards should be taken into account and used, if possible. In some cases, when this is sufficient, others can be used: the construction of concrete barrier dams, forest plantations, barrier shafts made of large stones, breakwaters, etc.