The Truth about Earthquake
Every year several hundred thousands of earthquakes occur on our planet. Most of them are so small and insignificant that they can only be captured by special sensors. But there are also more serious fluctuations: twice a month the earth crust shakes hard enough to destroy everything around.
As the majority of such impulses with big forces occur at the bottom of the oceans, if they are not accompanied by a tsunami, people even do not know about them. But when the land shudders, the element can be so devastating that the number of victims comes to thousands, as it happened in the XVI century in China (during the 8.1-magnitude quake, the number of killed was more than 830 thousand of people).
Causes of disasters
Earthquake it is the tremors and vibrations of the earth's crust, caused by natural or artificially created reasons (the movement of lithospheric plates, volcanic eruptions, explosions). Effects of high-intensity impulses are often disastrous, the number of victims can be surpassed only by Typhoon.
Unfortunately, at the moment, scientists have not studied processes that are happening in the bowels of our planet very well, and therefore prediction of earthquakes are rather rough and too much general. Among the causes of earthquakes specialists distinguish tectonic, volcanic, landslip, artificial and man-caused fluctuations of the Earth's crust.
Most of the earthquakes that have been recorded appeared as a result of movements of tectonic plates, when there is a sharp shift of rocks. This can be a collision with each other, and the lowering of a thin plate under another one. Although usually this shift is small, only a few centimeters, mountains above epicenter come in motion, which gives release to enormous power of energy. As a result, the earth's surface cracks, huge tracts of land start to shift, together with all that therein - fields, houses, people and others.
Volcanic vibration is weak, but it can continue for a long time. Usually they are not very dangerous, nevertheless some big disastrous have been recorded. As a result of the most powerful volcanic eruption of Krakatoa in the late XIX century, half of the mountain was destroyed by explosion, and subsequent tremors were so strong that had splited the island into three parts, burying two-thirds of it into the abyss. After earthquake, huge tsunami raised and destroyed completely all those who managed to survive until then and did not have time to leave the danger area.
It is impossible not to mention the great landslip and landslides. Typically, these concussions are not strong, but in some cases the consequences are disastrous. So, once similar case occurred in Peru, when a huge avalanche, caused by the earthquake, at a speed of 400 km / h went down from the mountain Askarali, and razed to the ground more than one village, killed more than eighteen thousand people.
4. Man-made or technogenic
In some cases, the causes and consequences of earthquakes are often associated with human activity.
Scientists had recorded growth in the number of tremors in areas of large reservoirs. This is connected to the fact that the collected mass of water begins to give pressure to the earth's crust and water penetrates through ground - destroying it. In addition, an increase in seismic activity has been observed in the field of oil and gas, as well as in the area of mines and quarries.
Earthquakes can also be caused in an artificial way. For example, after the North Korea tested new nuclear weapons, in many places of the planet sensors recorded earthquakes of moderate intensity.
Underwater earthquakes occur during the collision of tectonic plates on the ocean floor or near the coast. If the focus is shallow, and the magnitude is equal to 7 points, undersea earthquake is extremely dangerous because it causes a tsunami. During shuddering of sea bottom crust one part goes down, the other - is raised, as a result, water in an attempt to return to the original position, starts to move vertically, causing a series of huge waves coming towards the coast.
At the beginning…
The earthquake is a gap, after its formation earth's surface is instantly shifted. It should be noted that the gap does not occur immediately. At first plates encounter on each other, whereby friction is generated and energy appears, which gradually begins to accumulate.
When the voltage reaches its maximum and starts to exceed the frictional force, the rocks start to get broken, and then the released energy is converted into seismic waves moving at a speed of 8 km / sec that causes tremors.
Earthquake characteristic by the depth of epicenter is divided into three groups:
1) Normal – the depth of epicenter is up to 70 km;
2) Intermediate – the depth of epicenter is up to 300 km;
3) Deep – the depth of epicenter is over 300 km, this is typical for the Pacific Rim. The deeper is the epicenter, the more far distance will be reached by seismic waves that were generated by energy.
Earthquake consists of several stages. Basically, the strongest tremors preceded by warning fluctuations (foreshocks), followed by the starting aftershocks, further shaking, with the magnitude of the strongest aftershock by 1,2 smaller than the main shock. The period from the beginning of foreshocks to the end of aftershocks may last for several years, as, for example, this happened in the end of XIX century on the island of Lissa in the Adriatic sea: it lasted three years and in that time, scientists have recorded 86 000 impulses.
As for the duration of the main shock, it is usually not long-lasting, and rarely lasts more than a minute. For example, the most powerful impulse happened in Haiti, it took place a few years ago and lasted for forty seconds - and that was enough to turn the city of Port-au-Prince in ruins.
To find out exactly what impetus would be a major and will have the greatest magnitude, is extremely difficult, problematic, and there is no way to be sure on hundred percent. Therefore, strong earthquakes often catch people by surprise. For example, it happened in 2015 in Nepal, in a country where weak tremors were recorded so many times that people simply do not pay much attention to them. Therefore shudder of ground with magnitude of 7.9 points resulted with a large number of casualties.
Magnitude of the earthquake
One of the ways to measure the vibration amplitude and the amount of released energy is the scale of magnitude (Richter scale), which contains conventional units from 1 to 9.5.
The carried out calculations have shown that the size of the epicenter during weak surface oscillations in the length and in the vertical is measured by several meters, when middle power - kilometers. But the earthquake, which causing the disasters, have length up to one thousand kilometers and go from point gap to a depth up to fifty kilometers. Thus, the maximum reported size of the earthquake’s epicenter on our planet was 1000 per 100 kilometers.
This is how magnitude of the earthquakes (Richter scale) looks like:
2 – weak and almost insensible fluctuations;
4 - 5 – even if shocks are week, they can lead to slight disruptions;
6 - medium destruction;
8.5 - one of the strongest recorded earthquakes.
The Great Chilean earthquake is considered to be the largest one, with its magnitude of 9.5, it has spawned a tsunami that passed the Pacific Ocean to get to Japan, overcame 17 thousand kilometers.
What to do in cases of earthquakes
1) a person must immediately leave the building and go to the an open place where there are no electrical wires.
2) If a person can not leave the building, it should avoid the elevator and stairs. Most safety place is near the load-bearing walls.
3) You can not stand in the doorway, sooner or later it will crash.
4) It is better not to hide under tables or other furniture, person is risking to be crushed by it. The best way is to stay close to the rugged furniture, a sofa or table will approach, so when wall or ceiling will crash down they will not squash the furniture at all, little free space will be created around it.
5) Animals instinctively try to curl up and take as less space as possible. The person should also lie on the floor in a pose of uterine baby next to the bed or a large armchair.
6) As soon as the earthquake stopped the man should immediately leave the building, because the new aftershocks may follow.
7) Try not to panic and believe in rescue.