The news that came from Italy in the late summer of 2016 made the whole world shudder. A terrible earthquake struck near the town of Perugia. The hardest blow fell on the village of Akkumuli, which was very close to the epicenter of the earthquake. Three quarters of its buildings disappeared from the face of the earth, the rest were seriously damaged.
Such earthquakes usually occur no more than once a year, but less significant disasters occur more often. If we talk about all the earthquakes that are recorded on our planet throughout the year, then their number is simply amazing - there are hundreds of thousands of them! It is only in folklore that our Earth is considered stable and unshakable. And what do we see with our own eyes? What is the cause of severe cataclysms?
Why do earthquakes happen
For a long time mankind has been trying to explain the nature of the tremors. For some time, natural disasters were attributed to supernatural properties. For example, the tribes inhabiting Siberia believed that tremors caused giant monsters living in the bowels of our planet. How can we not recall the Kola superdeep borehole and the voices from hell emanating from it?
Turkmen legends speak of a dragon causing an earthquake with its heavy gait. In ancient Russian legends, you can find a mention of whales that hold the earthly firmament. According to legend, whales, tossing and turning from side to side, provoked earthquakes.
From the point of view of modern science, an earthquake is a vibration of the earth's crust, which can be caused by a wide variety of reasons (tectonic shifts, volcanic activity, etc.). Basically, earthquakes are divided into three types.
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Landfall earthquakes
Well-known rocks such as salt and limestone are found in many places. After their dissolution by groundwater, voids, cracks and caves of impressive size appear. There comes a time when the upper layers cannot withstand the pressure of the layers and collapse.
This is how an earthquake or a series of tremors occurs, called a landslide earthquake. A mountain collapse can easily be the cause of a natural phenomenon. It should be noted that such earthquakes occur only in the nearby area and do not have much strength.
Volcanic earthquakes
They are provoked by volcanic eruptions. Despite their impressive destructive power, their area of action is limited only to the area adjacent to the volcano. The only exception is a supervolcano eruption, like the one that can form in the Yellowstone National Park. The echoes of such an event, if it decides to happen, will be heard in different parts of the continent.
Tectonic earthquakes
They cover an area of up to 1,000,000 km2 and are incredibly powerful. The cause of a tectonic earthquake is the mixing of huge areas of the earth's crust. Substances in the underground are constantly moving. As they rise to the surface of the earth, they make the earth's crust bend. Such movements are imperceptible to the eye, but there comes a time when they break the rock layers.
Consider the causes of the disaster that befell sunny Italy. The Tyrrhenian Sea to the west of Italy separates this country from the islands of Corsica and Sardinia, while gradually expanding. The pressure on the fault, which falls on the Apennine mountain range, increases. On the opposite side, a movement is observed, in which the plate "slides" under Italy. As a result, the largest fault was formed, over which the city of Perugia is located.
What is an earthquake?
When bending the rod, we feel resistance, which constantly increases until the rod breaks. A similar story happens with rocks. When an individual piece of land rises and the adjacent one sinks, the elastic force increases until the formation fractures occurs. In some cases, cracks protrude on the earth's surface, and sometimes they form at a depth of up to 10 kilometers or more.
It happens that rocks move to a great height. At the beginning of the last century, the city of San Francisco was destroyed by a terrible earthquake. Huge layers of earth sank 7 meters or more. Seismologists know that the area of oceanic trenches and young mountains is the area where earthquakes occur most often.
How to measure tremors?
Attempts to classify earthquakes by strength have been made many times. In the late 19th century, the Italian scientist Giuseppe Mercali developed a 12-point earthquake scale. It is still used in the United States today. Europeans use the EMS-98 12-point earthquake scale. In Japan, the scale starts at three points, and the highest point in this system is 7.
What is the probability of predicting a disaster?
At the moment, all the reasons for the occurrence of tremors are well known to science. A completely natural question arises: is it possible to predict an earthquake, and thereby save an incredible number of people from the consequences of a colossal disaster?
Long-term observations made it possible to identify seismic zones and establish the estimated strength of an earthquake in a particular area, which contributed to the emergence of seismic zoning maps. And only one important factor is missing for making an accurate forecast - the time of the beginning of the disaster. To determine it, one should thoroughly study the structure of the earth's interior, which is technically difficult today.
Russia has nothing to fear
On our planet, in addition to earthquake zones, there are gigantic territories where tremors are practically not observed. These areas primarily include the East European Plain, on the territory of which St. Petersburg and Moscow are located, and the West Siberian Lowland. These platforms are earthquake resistant. Residents of the CIS countries can also feel safe, at least until our planet is comprehended by global changes.