Some people still think that earthquakes are a rare and unusual phenomenon. This is far from true. Severe, catastrophic earthquakes really do not happen very often - 1-2 times a year; weaker ones - much more often. Total for globe Hundreds of thousands of earthquakes occur every year! It turns out that our Earth, which appears in folk tales, proverbs and sayings as a symbol of inviolability and stability, is in fact not so immutable. People have been wondering for a long time: what are the causes these menacing natural phenomena - earthquakes?
Possible causes of the earthquake
Attempts to explain the causes of earthquakes were made already in ancient times and were reflected in various peoples in numerous legends and traditions. For a long time the origin of earthquakes was explained by supernatural causes. Thus, among the tribes that inhabited Siberia, there was an idea that earthquakes were caused by giant underground monsters. The legends widespread among the Turkmen told about a monstrous dragon. When he walks on the ground, it shakes and trees burst with a crash. IN ancient Russian sources talked about whales on which the Earth supposedly rests. When whales turn from side to side, they earth's surface echoes of this noise are heard - an earthquake occurs. Churchmen used earthquakes, along with other menacing natural phenomena, as proof of the power of God, explaining them as “God’s punishment” sent to people for their sins.
Scientific approach
Causes earthquakes are easy to name, if you turn to science to find out the opinion of scientists. An earthquake is fluctuations earth's crust caused by for various reasons. Depending on them There are three types of earthquakes:
- Landslides.
Found in many places rocks, water soluble eg limestone, salt. The groundwater They gradually dissolve them, and over time, cracks, voids, and caves form underground. They often reach significant sizes. Eventually, the roof of the cave may not be able to withstand the pressure of the layers located above and collapse. In this case, an underground shock or even a series of tremors occurs - an earthquake. The source of a landslide earthquake can be other phenomena, for example, a landslide in the mountains. Earthquakes of this type have little strength and are felt only in close proximity from the site of the collapse.
- Volcanic.
Volcanic eruptions, which are quite formidable natural phenomena in themselves, are very often accompanied by earthquakes. They are often destructive, but their distribution is usually limited to a small area adjacent to the volcano.
- Tectonic.
Most often, earthquakes are not associated with landslides or volcanic eruptions. These are the so-called tectonic earthquakes - the most strong earthquakes, sometimes covering areas of millions square kilometers. They are caused by movements of vast areas of the earth's crust. And these movements are caused by the fact that the matter in the bowels of the globe is in continuous movement. Where it rises, the earth's crust bends upward; Where matter sinks, the earth's crust also sinks. These movements, completely invisible to the eye, ultimately lead to the rupture of rock layers.
Thus, the causes of earthquakes are: rock falls (and consequent tremors), volcanic eruptions, but main reason Most earthquakes are movements of large areas of the earth's crust.
What is the cause of destruction during an earthquake?
Imagine that you are bending a flexible rod with your hands. At first it bends. The further you go, the stronger the resistance of the rod; Finally, it breaks with a crash. Much the same thing happens with rocks. If one section of the earth's crust rises and the neighboring one falls, then elastic forces gradually accumulate, which ultimately lead to rupture of the layers. However, these breaks and cracks are not always visible on the earth's surface. It happens that they pass at a depth of tens of kilometers from the surface of the earth.
Sometimes rocks move along the formed cracks to a considerable height, which is clearly visible on the surface. In 1906, a catastrophic earthquake destroyed the city of San Francisco. First, a fault in the earth's crust formed. During the earthquake along the fault line, gigantic layers of earth dropped in places up to 7 m. In Assam (India), during a very strong earthquake, a section of the earth's crust dropped by more than 10 m and a so-called fault was formed over tens of miles. Apparently, such movements more often occur where cracks, faults, and shifts previously occurred and where the earth’s crust is already weakened.
Earthquakes are usually observed in areas of young folded mountains, where the movement of matter in the earth's interior is especially active. Areas prone to earthquakes oceanic trenches, what is the cause of destruction during an earthquake.
In the Pacific Ocean, along island arcs and continental coasts stretch deep-sea trenches. There are high young mountains adjacent to these areas of the ocean. Apparently further development these mountains and depressions and determines frequent earthquakes on the shores of the Pacific Ocean. Often, a crack formed as a result of a tectonic earthquake opens an outlet for magma to the earth's surface. This is how a volcano arises.
Along with areas prone to earthquakes, there are vast areas where they almost never occur. Such aseismic areas are said to include, for example, the East European Plain, where Moscow and St. Petersburg are located, and West Siberian Lowland. They are so-called platforms, stable sections of the earth's crust.
Possible consequences of earthquakes
Earthquakes bring enormous disasters to people, destroying entire areas. Possible consequences of earthquakes are so severe that the affected states have to develop plans for economic recovery, as usually happens after wars:
- walls of houses collapse, cities are destroyed;
- Residents are dying under the rubble of houses;
- earthquake causes significant changes in terrain seabed. The vibrations of the seabed, in turn, set in motion huge masses of water, forming a tsunami;
- Communication is interrupted, electricity supply is cut off, water supply system fails;
- roads, buildings, bridges are destroyed;
- Huge cracks form on the earth's surface;
- aftershocks can cause landslides and landslides in the mountains;
- earthquakes cause topographical changes in topography: new mountains, rivers, lakes appear, and some that previously existed disappear. New islands are appearing in the sea, while others that were recently on the maps are disappearing under the water.
Protection against the consequences of earthquakes
So, immediate reasons and possible consequences earthquakes known to science. Is it not possible to predict earthquakes and thereby prevent the colossal disasters that befall people from time to time? This question has occupied scientists for a long time. As a result of long-term observations, seismically dangerous areas, that is, prone to strong earthquakes, have been identified: Crimea, Caucasus, Pamir, Tien Shan, Baikal region, Kuril-Kamchatka arc and some others.
It is known exactly how strong earthquakes can occur in a particular seismic area. This makes it possible to draw up special seismic zoning maps, which indicate areas prone to earthquakes and indicate their possible strength. Thus, to make an earthquake forecast, only one factor is missing - the time of the earthquake's onset. In order to learn to predict this, it is necessary to better know the structure of the earth's interior.
But if it is not yet possible to prevent or accurately predict an earthquake, then it is already possible to fight it destructive actions. It has been established that the use of certain materials in construction, such as reinforced concrete, and the use of special building structures can significantly reduce and sometimes even prevent their destruction. Anti-seismic construction is now being carried out in earthquake-prone areas. There are no multi-storey buildings being built there. Houses are built on reinforced foundations with lightweight roofs. The brick walls are connected with reinforced concrete belts. All these measures significantly increase the reliability of buildings, and they do not fall apart during earthquakes.
This, of course, is not all measures to protect against the consequences of earthquakes: in the future, scientists will be able to accurately predict the onset of earthquakes and thousands of people will be saved from death. Thus, science equips people with increasingly powerful means to combat natural disasters and relieves them of fear of menacing natural phenomena.
The strongest earthquakes throughout human history have caused colossal material damage and caused a huge number of casualties among the population. The first mention of tremors dates back to 2000 BC.
And despite the achievements modern science and the development of technology, no one can still predict exact time, when the elements strike, so quick and timely evacuation of people often becomes impossible.
Earthquakes are natural disasters that kill the most people, much more than, for example, hurricanes or typhoons.
In this rating we will talk about the 12 most powerful and destructive earthquakes in human history.
12. Lisbon
On November 1, 1755, in the capital of Portugal, the city of Lisbon, it happened major earthquake, later called the Great Lisbon Earthquake. A terrible coincidence was that on November 1 - All Saints' Day, thousands of residents gathered for mass in the churches of Lisbon. These churches, like other buildings throughout the city, could not withstand the powerful shocks and collapsed, burying thousands of unfortunates under their rubble.
Then a 6-meter tsunami wave rushed into the city, covering the surviving people rushing in panic through the streets of destroyed Lisbon. The destruction and loss of life were colossal! As a result of the earthquake, which lasted no more than 6 minutes, the tsunami it caused and numerous fires that engulfed the city, at least 80,000 residents of the Portuguese capital died.
Many famous figures and philosophers touched on this deadly earthquake in their works, for example, Immanuel Kant, who tried to find scientific explanation such a massive tragedy.
11. San Francisco
On April 18, 1906, at 5:12 am, powerful tremors shook sleeping San Francisco. The force of the tremors was 7.9 points and as a result of the strongest earthquake in the city, 80% of the buildings were destroyed.
After the first count of the dead, authorities reported 400 victims, but later their number increased to 3,000 people. However, the main damage to the city was caused not by the earthquake itself, but by the monstrous fire it caused. As a result, more than 28,000 buildings throughout San Francisco were destroyed, with property damage amounting to more than $400 million at the exchange rate of that time.
Many residents themselves set fire to their dilapidated houses, which were insured against fire, but not against earthquakes.
10. Messina
The largest earthquake in Europe was the earthquake in Sicily and Southern Italy, when on December 28, 1908, as a result of powerful tremors measuring 7.5 on the Richter scale, according to various experts, from 120 to 200,000 people died.
The epicenter of the disaster was the Strait of Messina, located between the Apennine Peninsula and Sicily; the city of Messina suffered the most, where practically not a single surviving building remained. A huge tsunami wave, caused by tremors and amplified by an underwater landslide, also caused a lot of destruction.
Documented fact: rescuers were able to pull two exhausted, dehydrated, but alive children from the rubble, 18 days after the disaster struck! Numerous and extensive destruction was caused primarily by low quality buildings in Messina and other parts of Sicily.
Russian sailors provided invaluable assistance to the residents of Messina imperial fleet. Ships included study group sailed on Mediterranean Sea and on the day of the tragedy they ended up in the port of Augusta in Sicily. Immediately after the tremors, sailors organized a rescue operation and thanks to their brave actions, thousands of residents were saved.
9. Haiyuan
One of the most deadly earthquakes in the history of mankind, there was a devastating earthquake that struck Haiyuan County, part of Gansu Province, on December 16, 1920.
Historians estimate that at least 230,000 people died that day. The force of the tremors was such that entire villages disappeared in the faults of the earth’s crust, such big cities like Xi'an, Taiyuan and Lanzhou. Incredibly, strong waves formed after the disaster were recorded even in Norway.
Modern researchers believe that the death toll was much higher and totaled at least 270,000 people. At that time, this was 59% of the population of Haiyuan County. Several tens of thousands of people died from the cold after their homes were destroyed by the elements.
8. Chile
The earthquake in Chile on May 22, 1960, considered the strongest earthquake in the history of seismology, measured 9.5 on the Richter scale. The earthquake was so powerful that it caused tsunami waves more than 10 meters high, which covered not only the coast of Chile, but also caused enormous damage to the city of Hilo in Hawaii, and some of the waves reached the coasts of Japan and the Philippines.
More than 6,000 people died, most of whom were hit by the tsunami, and the destruction was unimaginable. 2 million people were left homeless and the damage amounted to more than $500 million. In some areas of Chile, the impact of the tsunami wave was so strong that many houses were carried away 3 km inland.
7. Alaska
On March 27, 1964, the most powerful earthquake in American history occurred in Alaska. The magnitude of the earthquake was 9.2 on the Richter scale and this earthquake was the strongest since the disaster struck Chile in 1960.
129 people died, of which 6 were victims of tremors, the rest were washed away by a huge tsunami wave. The disaster caused the greatest destruction in Anchorage, and tremors were recorded in 47 US states.
6. Kobe
The Kobe earthquake in Japan on January 16, 1995 was one of the most destructive in history. Tremors with a magnitude of 7.3 began at 05:46 am local time and continued for several days. As a result, more than 6,000 people died and 26,000 were injured.
The damage caused to the city's infrastructure was simply enormous. More than 200,000 buildings were destroyed, 120 of the 150 berths in the port of Kobe were destroyed, and there was no power supply for several days. The total damage from the disaster was about $200 billion, which at that time was 2.5% of Japan's total GDP.
Not only government services rushed to help the affected residents, but also the Japanese mafia - the Yakuza, whose members delivered water and food to those affected by the disaster.
5. Sumatra
December 26, 2004, huge tsunami, which hit the shores of Thailand, Indonesia, Sri Lanka and other countries, was caused by a devastating earthquake measuring 9.1 on the Richter scale. The epicenter of the tremors was located in Indian Ocean, near the island of Simeulue, off the northwestern coast of Sumatra. The earthquake was unusually large; the earth's crust shifted at a distance of 1200 km.
The height of the tsunami waves reached 15-30 meters and victims of the disaster various estimates became from 230 to 300,000 people, although the exact number of deaths is impossible to calculate. Many people were simply washed into the ocean.
One of the reasons for such a number of casualties was the lack of an early warning system in the Indian Ocean with which to report to the local population about the approach of a tsunami.
4. Kashmir
On October 8, 2005, the worst earthquake to hit South Asia in a century occurred in the Pakistani-controlled region of Kashmir. The strength of the tremors was 7.6 on the Richter scale, which is comparable to the San Francisco earthquake in 1906.
As a result of the disaster, according to official data, 84,000 people died, according to unofficial data, more than 200,000. Rescue work were hampered by the military conflict between Pakistan and India in the region. Many villages were completely wiped off the face of the earth, and the city of Balakot in Pakistan was completely destroyed. In India, 1,300 people became victims of the earthquake.
3. Haiti
On January 12, 2010, an earthquake measuring 7.0 on the Richter scale occurred in Haiti. Basic the blow fell to the capital of the state - the city of Port-au-Prince. The consequences were terrible: almost 3 million people were left homeless, all hospitals and thousands of residential buildings were destroyed. The number of victims was simply enormous, according to various estimates from 160 to 230,000 people.
Criminals who had escaped from a prison destroyed by the elements poured into the city; cases of looting, robberies and robberies became frequent on the streets. Material damage from the earthquake is estimated at 5.6 billion dollars.
Despite the fact that many countries - Russia, France, Spain, Ukraine, the USA, Canada and dozens of others - provided all possible assistance in eliminating the consequences of the disaster in Haiti, more than five years after the earthquake, more than 80,000 people still live in improvised camps for refugees.
Haiti is poorest country V western hemisphere and this disaster dealt an irreparable blow to the economy and living standards of citizens.
2. Earthquake in Japan
On March 11, 2011, the strongest earthquake in Japanese history occurred in the Tohoku region. The epicenter was east of the island Honshu and the strength of the tremors was 9.1 on the Richter scale.
As a result of the disaster, the nuclear power plant in the city of Fukushima was severely damaged and power units at reactors 1, 2, and 3 were destroyed. Many areas became uninhabitable as a result of radioactive radiation.
After underwater tremors, a huge tsunami wave covered the coast and destroyed thousands of administrative and residential buildings. More than 16,000 people died, 2,500 are still considered missing.
The material damage was also colossal - more than $100 billion. And given that the complete restoration of the destroyed infrastructure may take years, the amount of damage may increase several times.
1. Spitak and Leninakan
There are many tragic dates in the history of the USSR, and one of the most famous is the earthquake that shook the Armenian SSR on December 7, 1988. Powerful tremors in just half a minute almost completely destroyed the northern part of the republic, capturing the territory where more than 1 million inhabitants lived.
The consequences of the disaster were monstrous: the city of Spitak was almost completely wiped off the face of the Earth, Leninakan was severely damaged, more than 300 villages were destroyed and 40% of the republic’s industrial capacity was destroyed. More than 500 thousand Armenians were left homeless, according to various estimates, from 25,000 to 170,000 residents died, 17,000 citizens remained disabled.
111 states and all republics of the USSR provided assistance in the restoration of destroyed Armenia.
Movements within the earth's crust lead to earthquakes—shakes of the earth's surface. They may be associated with volcanic activity or with movements of their parts. The center of an earthquake can be deep under the Earth's surface - at a depth of several hundred kilometers, in which case they are felt quite weakly on the surface. The greatest destructive force have those earthquakes that occur at a depth of 20-50 km. The place on the earth's surface closest to the center of the earthquake is called the epicenter - it is at this point that the earthquake is strongest.
Hundreds of thousands of earthquakes are recorded around the globe every year. However, most of them are weak and we do not notice them. The strength of earthquakes is assessed by the intensity of destruction on the Earth's surface and measured on a twelve-point scale.
Earthquakes with a magnitude of 1-2 go unnoticed by most people, but they can be felt by animals that are more sensitive to movements of the earth's surface.
Tremors with a force of 3 are felt only by people who are at rest, and a force of 4 is felt by everyone.
Earthquakes of magnitude 5 cause the movement of light objects (for example, dishes), chandeliers sway, and unlocked doors slam.
Earthquakes with a magnitude of 6-7 cause damage to buildings, but the walls remain intact. Structures created taking into account seismic activity, withstand such earthquakes.
6-9 points lead to serious destruction of houses, people find it difficult to stand on their feet, and landslides occur in the mountains.
At 10-11 points, any structures turn into ruins, roads, pipelines, railway rails are severely damaged, and the ground cracks.
12 points are the most destructive earthquakes, leading to the complete destruction of settlements and severe changes in the relief (rocks, crevices, lakes appear, rivers change their courses).
Created to measure earthquakes special device which is called seismograph. It registers the slightest vibrations of the earth's crust.
With the help of seismographs, it is possible to predict in a few hours, since any eruption begins with tremors within the earth's crust, after which magma rushes upward.
Signs of a coming earthquake
- the smell of gas in an area where it had not been noticed before,
- disturbance of birds and domestic animals,
- flashes in the form of scattered lightning lightning,
- sparking of nearby but not touching electrical wires,
- bluish glow inner surface walls of houses;
- spontaneous combustion of fluorescent lamps.
There are areas of increased seismic activity - those in which earthquakes occur more often. In Russia it is, Southern Siberia. Special precautions are taken in such areas. Firstly, the probability of an earthquake is taken into account when constructing housing and other structures, since it is the destruction of buildings that causes the most serious damage during an earthquake. Secondly, mechanisms are being created to quickly alert the population, especially in areas with high volcanic activity.
It is no less dangerous if the epicenter of the earthquake is in the ocean, since in this case huge waves up to 30 m high arise.
In the open sea or ocean, tsunamis are not dangerous, therefore, if there is danger, all ships in the port immediately go to sea. On the coast, these huge waves cause serious destruction.
Hundreds of thousands of earthquakes occur on our planet every year. Most of them are so small and insignificant that only special sensors can detect them. But there are also more serious fluctuations: twice a month the earth’s crust shakes violently enough to destroy everything around it.
Since most tremors of such force occur at the bottom of the World Ocean, unless they are accompanied by a tsunami, people are not even aware of them. But when the land shakes, the disaster is so destructive that the number of victims runs into the thousands, as happened in the 16th century in China (more than 830 thousand people died during earthquakes of magnitude 8.1).
Earthquakes are underground tremors and vibrations of the earth's crust caused by natural or artificially created causes (movement lithospheric plates, volcanic eruptions, explosions). The consequences of high-intensity tremors are often catastrophic, second only to typhoons in terms of the number of victims.
Unfortunately, on this moment Scientists have not studied the processes that occur in the depths of our planet so well, and therefore the forecast of earthquakes is rather approximate and inaccurate. Among the causes of earthquakes, experts identify tectonic, volcanic, landslide, artificial and man-made vibrations of the earth's crust.
Tectonic
Most of the earthquakes recorded in the world arose as a result of movements tectonic plates when there is a sharp displacement of rocks. This can be either a collision with each other, or a thinner plate being lowered under another.
Although this shift is usually small, amounting to only a few centimeters, the mountains located above the epicenter begin to move, releasing enormous energy. As a result, cracks form on the earth's surface, along the edges of which huge areas of the earth begin to shift, along with everything that is on it - fields, houses, people.
Volcanic
But volcanic vibrations, although weak, continue for a long time. Usually they do not pose any particular danger, but catastrophic consequences have still been recorded. As a result of the powerful eruption of the Krakatoa volcano in late XIX Art. the explosion destroyed half the mountain, and the subsequent tremors were so powerful that they split the island into three parts, plunging two-thirds into the abyss. The tsunami that arose after this destroyed absolutely everyone who had managed to survive before and did not have time to leave the dangerous territory.
Landslide
It is impossible not to mention landslides and large landslides. Usually these tremors are not severe, but in some cases their consequences can be catastrophic. So, it happened once in Peru, when a huge avalanche, causing an earthquake, came down from Mount Ascaran at a speed of 400 km/h, and, having leveled more than one settlement, killed more than eighteen thousand people.
Technogenic
In some cases, the causes and consequences of earthquakes are often associated with human activity. Scientists have recorded an increase in the number of tremors in areas of large reservoirs. This is due to the fact that the collected mass of water begins to put pressure on the underlying earth’s crust, and water penetrating through the soil begins to destroy it. In addition, an increase in seismic activity has been noticed in oil and gas production areas, as well as in the area of mines and quarries.
Artificial
Earthquakes can also be caused artificially. For example, after the DPRK tested a new nuclear weapon, in many places on the planet, sensors recorded moderate earthquakes.
An undersea earthquake occurs when tectonic plates collide on the ocean floor or near the coast. If the source is shallow and the magnitude is 7, an underwater earthquake is extremely dangerous because it causes a tsunami. During the shaking of the sea crust, one part of the bottom falls, the other rises, as a result of which the water, in an attempt to return to its original position, begins to move vertically, generating a series of huge waves moving towards the coast.
Such an earthquake together with a tsunami can often have catastrophic consequences. For example, one of the most powerful seaquakes occurred several years ago in the Indian Ocean: as a result of underwater tremors, big tsunami and, hitting the nearby coasts, led to the death of more than two hundred thousand people.
The tremors begin
The source of an earthquake is a rupture, after the formation of which the earth's surface instantly shifts. It should be noted that this gap does not occur immediately. First, the plates collide with each other, resulting in friction and energy that gradually begins to accumulate.
When the stress reaches its maximum and begins to exceed the frictional force, the rocks rupture, after which the released energy is converted into seismic waves moving at a speed of 8 km/s and causing vibrations in the earth.
The characteristics of earthquakes based on the depth of the epicenter are divided into three groups:
- Normal – epicenter up to 70 km;
- Intermediate – epicenter up to 300 km;
- Deep-focus - the epicenter at a depth exceeding 300 km, typical of the Pacific Rim. The deeper the epicenter, the further the seismic waves generated by the energy will reach.
Characteristic
An earthquake consists of several stages. The main, most powerful shock is preceded by warning vibrations (foreshocks), and after it, aftershocks and subsequent tremors begin, and the magnitude of the strongest aftershock is 1.2 less than that of the main shock.
The period from the beginning of foreshocks to the end of aftershocks may well last several years, as, for example, happened at the end XIX century on the island of Lissa in the Adriatic Sea: it lasted three years and during this time scientists recorded 86 thousand tremors.
As for the duration of the main shock, it is usually short and rarely lasts more than a minute. For example, the most powerful shock in Haiti, which occurred several years ago, lasted forty seconds - and this was enough to turn the city of Port-au-Prince into ruins. But in Alaska, a series of tremors were recorded that shook the earth for about seven minutes, with three of them leading to significant destruction.
Calculating which shock will be the main one and will have the greatest magnitude is extremely difficult, problematic, and there are no absolute methods. Therefore, strong earthquakes often take the population by surprise. This, for example, happened in 2015 in Nepal, in a country where mild tremors were recorded so often that people simply did not pay attention to them special attention. Therefore, a ground shaking with a magnitude of 7.9 led to a large number of victims, and the weaker aftershocks with a magnitude of 6.6 that followed it half an hour later and the next day did not improve the situation.
It often happens that the strongest tremors occurring on one side of the planet shake the opposite side. For example, the 2004 magnitude 9.3 earthquake in the Indian Ocean relieved some of the increasing stress on the San Andreas Fault, which is located at the junction of lithospheric plates along the California coast. It turned out to be so strong that it slightly modified the appearance of our planet, smoothing out its bulge in the middle part and making it more rounded.
What is magnitude
One way to measure the amplitude of oscillations and the amount of energy released is the magnitude scale (Richter scale), containing arbitrary units from 1 to 9.5 (it is very often confused with a twelve-point intensity scale, measured in points). An increase in the magnitude of earthquakes by just one unit means an increase in the amplitude of vibrations by ten, and energy by thirty-two times.
The calculations showed that the size of the epicenter during weak surface vibrations, both in length and vertically, is measured at several meters, when medium strength– kilometers. But earthquakes that cause disasters have a length of up to 1 thousand kilometers and extend from the rupture point to a depth of up to fifty kilometers. Thus, the maximum recorded size of the epicenter of earthquakes on our planet was 1000 by 100 km.
The magnitude of earthquakes (Richter scale) looks like this:
- 2 – weak, almost imperceptible vibrations;
- 4 - 5 - even though the shocks are weak, they can lead to minor damage;
- 6 – medium damage;
- 8.5 - one of the strongest recorded earthquakes.
- The largest earthquake is considered to be the Great Chilean earthquake with a magnitude of 9.5, which generated a tsunami that, having overcome Pacific Ocean, reached Japan, covering 17 thousand kilometers.
Focusing on the magnitude of earthquakes, scientists claim that out of the tens of thousands of vibrations that occur on our planet per year, only one has a magnitude of 8, ten - from 7 to 7.9, and a hundred - from 6 to 6.9. It must be taken into account that if the earthquake magnitude is 7, the consequences can be catastrophic.
Intensity scale
To understand why earthquakes occur, scientists have developed an intensity scale based on external manifestations, as an impact on people, animals, buildings, nature. The closer the epicenter of earthquakes is to the earth's surface, the greater the intensity (this knowledge makes it possible to give at least an approximate forecast of earthquakes).
For example, if the magnitude of the earthquake was eight and the epicenter was at a depth of ten kilometers, the intensity of the earthquake would be between eleven and twelve. But if the epicenter was located at a depth of fifty kilometers, the intensity will be less and will be measured at 9-10 points.
According to the intensity scale, the first destruction can occur already with magnitude six shocks, when thin cracks appear in the plaster. An earthquake of magnitude 11 is considered catastrophic (the surface of the earth's crust becomes covered with cracks and buildings are destroyed). The strongest earthquakes, capable of significantly changing the appearance of the area, are estimated at twelve points.
What to do during earthquakes
According to rough estimates by scientists, the number of people who have died in the world due to earthquakes over the past half-millennium exceeds five million people. Half of them are in China: it is located in a zone of seismic activity, and people live on its territory big number people (in the 16th century, 830 thousand people died, in the middle of the last century - 240 thousand).
Such catastrophic consequences could have been prevented if earthquake protection had been well designed state level, and when designing the buildings, the possibility of strong tremors was taken into account: most people died under the rubble. Often people living or staying in a seismically active zone have no the slightest idea about how exactly to act in conditions emergency and how you can save your life.
You need to know that if tremors find you in a building, you need to do everything possible to get out as quickly as possible. open space However, it is strictly forbidden to use elevators.
If it is impossible to leave the building, and the earthquake has already begun, leaving it is extremely dangerous, so you need to stand either in the doorway, or in a corner near a load-bearing wall, or crawl under a strong table, protecting your head with a soft pillow from objects that may fall from above. After the tremors are over, the building must be left.
If a person finds himself on the street during the onset of earthquakes, he must move away from the house by at least one third of its height and, avoiding tall buildings, fences and other buildings, move in the direction wide streets or parks. It is also necessary to stay as far away from downed electrical wires as possible. industrial enterprises, since explosive materials or toxic substances may be stored there.
But if the first tremors caught a person while he was in a car or public transport, need to leave urgently vehicle. If the car is in an open area, on the contrary, stop the car and wait out the earthquake.
If it so happens that you are completely covered in debris, the main thing is not to panic: a person can survive without food and water for several days and wait until they find him. After catastrophic earthquakes Rescuers work with specially trained dogs, and they are able to smell life among the rubble and give a sign.
10 most catastrophic volcanic eruptions
Volcano Unzen, 1792
The largest eruption of the Unzen volcano occurred in 1792. The volcanic eruption, earthquake and resulting tsunami killed 15,000 people.
200 years after this eruption the volcano was calm.
In 1991, the volcano became active again, the same year there was an eruption with the release of lava, killing 43 people, including a group of scientists and journalists. Japanese authorities were forced to evacuate thousands of residents. The volcano was active, spewing lava and ash, until about 1995. Since 1995, activity has decreased and it is currently in a static state.
Volcano El Chichon, Mexico, 1982
The eruption of El Chichon in 1982 killed 2,000 nearby residents in Chiapas, Mexico. After the eruption, a lake filled with sulfur formed in the crater of the volcano.
The peculiarity of the eruption of this volcano was that it was thrown into the atmosphere a large number of aerosols, about 20 million tons of this aerosol contained sulfuric acid.
The cloud entered the stratosphere and expanded it average temperature at 4 C, destruction of the ozone layer was also observed.
Volcano Pinatubo, Philippines, 1991
The 1991 eruption of Mount Pinatubo in the Philippines became the second largest eruption of the 20th century. The volcanic rating index was 6.
This is more than the eruption of St. Helens in 1980, but less than Tambora in 1815. Pinatubo, on June 15, 1991, released about two and a half cubic kilometers of material, including lava, ash and toxic gases. In total, about 10 square kilometers of material were ejected during the eruption. About 800 people died as a result of the eruption.
Mount St. Helens, USA, 1980
On May 18, 1980, Mount St. Helens began to erupt in the United States. The volcanic eruption killed 57 people (according to other sources, 62 people).
The release of gases into the atmosphere reached a height of 24 kilometers; before the eruption, an earthquake of magnitude 5.1 occurred, which caused a huge landslide.
The eruption lasted 9 hours. The released energy can be compared to the explosion energy of 500 atomic bombs, dropped on Hiroshima.
Volcano Nevada del Ruiz, Colombia, 1985
The eruption of Mount Nevada del Ruiz in 1985 killed 20,000 people in the nearby village of Armero. This is the second most fatal volcano in the 20th century.
The volcanic eruption melted the glacier on it, and the mudflow completely destroyed Armero.
But the tragedy happened first in the village of Chinchina - the authorities did not have time to completely evacuate the residents and 2,000 people died. The total death toll is estimated at between 23,000 and 25,000.
Kilauea Volcano, USA, 1983 (to date)
Kilauea Volcano may not be the most destructive, but what makes it special is that it has been erupting continuously for over 20 years, making it one of the most active volcanoes in the world. Based on the diameter of the crater (4.5 km), the volcano is considered the largest in the world.
Vesuvius exploded in 79, burying the entire city of Pompeii under a blanket of ash and pumice that fell from the sky for 24 hours. The ash layer reached 3 meters. By modern estimates 25,000 people became victims of the volcano. Excavations were carried out at the site of the city of Pompeii; such a number of victims was caused by the fact that people did not immediately begin to leave their homes, but tried to pack and save their property.
After 79, the volcano erupted dozens of times, last time in 1944.
Volcano Pelé exploded on the Caribbean island of Martinique in 1902, killing 29,000 people and destroying the entire city of Saint-Pierre. For several days, the volcano erupted gases and a small portion of ash, residents saw this, and on May 8, Pele exploded.
Witnesses on ships in the immediate vicinity of the coast described sudden appearance a massive mushroom-shaped cloud filled with fiery hot ash and volcanic gases, the emissions covered the island in a matter of seconds.
Only two people survived the volcano explosion.
Volcano Krakatoa, Indonesia, 1883
The explosion of Krakatoa in 1883 can be compared to the power of 13,000 atomic bombs.
More than 36,000 people died. The height of the ejected ash reached 30 km. After the eruption, the island seemed to have folded, that is, the island itself fell into the void under the volcano, all of this was covered by masses of ocean water. Since the surface temperature was high and the land subsided quickly, this led to the formation of a tsunami wave that moved towards the island of Sumatra, which led to the death of more than 2,000 people on it.
At the moment, in place of the old volcano, a new active volcano has formed, which is growing in height by 6-7 meters per year.
Volcano Tambora, Indonesia, 1815
The eruption of Mount Tambora was the largest volcanic eruption on record on the planet.
10,000 people died instantly from lava flows and toxic gases.
The total number of deaths from the volcano and tsunami is about 92,000 people, not counting those who died from the famine that followed.
The scale of the eruption is evidenced by the fact that the amount of material released into the earth's atmosphere was so large that there was no summer in the northern hemisphere in 1816.
The thing is that particles of matter reflected Sun rays and interfered with the warming of the Earth.
The consequence of the eruption was famine throughout the world.
The power of the eruption was 7 points on the scale of volcanic eruptions.