How to determine the proximity of an earthquake?
So what phenomena signify the spontaneous activity of the earth's interior? Let's try to consider some of them separately. Let's start with the signals captured by seismographs. Something is beginning to happen in the bowels of the earth. What could it be?
Experts believe that shortly before the impact of the elements, the picture of microseismic activity is changing. After all, the Earth is constantly "shaking." Each year, instruments record several million inconspicuous earthquakes for us. Perhaps, according to the characteristic picture of their distribution, it will be possible to trace how the element gathers its forces, prepares to strike a special blow. In any case, the International Institute of Earthquake Prediction Theory and Mathematical Geophysics of the Russian Academy of Sciences, created on the basis of the scientific group that existed at the Institute of Earth Physics since the 1960s, has been doing this for a long time. Such a technique is especially good because it allows observations to be made at a great distance from the epicenter of the earthquake.
Each year, devices record several million inconspicuous earthquakes for us.
Perhaps in the near future we will learn to predict at least some underwater earthquakes. The American geologist Jeffrey McGuire, analyzing the information collected in recent years, drew attention to the fact that earthquakes in the range of ridges in the eastern part of the Pacific Ocean are preceded by small tremors. They become the harbinger of the main blow of the elements. So, before the earthquake, which had a magnitude of 5.4, tremors were observed with a magnitude of at least 2.5.
Researchers even conducted a thought experiment. Processing data on seismic activity in this part of the Pacific Ocean for 1996-2001, they whenever they discovered tremors of similar strength predicted that an hour later a radius of 15 kilometers would have led to a more powerful earthquake. So they retroactively predicted six of the nine largest earthquakes in the vicinity of these underwater ridges in these years.
Another method of forecasting is almost inspired by biblical revelations. “There will be large earthquakes in places, and smooth, and pestilence, and terrible events, and great signs from heaven” (Luke 21: 11). In fact, on the eve of a powerful earthquake that erupted in Alaska on March 27, 1964, not only the “small worlds,” but scientists also saw "Great signs from heaven." Subsequently, experts recognized that sometimes, shortly before underground strikes, the electromagnetic properties of the ionosphere change. Could this help predict the trouble in time?
Using the example of several earthquakes - in particular, in Mexico (January 21, 2003) and the Indian state of Gujarat (January 26, 2001) - Russian scientist Sergei Pulinets showed that 5-7 days before the catastrophe, the concentration of free electrons in the ionosphere changes, and this affects the quality of satellite navigation system signals. But another thing turned out: this does not happen at all before every burst of seismic activity. In addition, storms in the Sun also influence the measurement results, that is, the GPS signal level. Using this method is like doing astronomical observations, being on the deck of the ship, where the slightest pitching introduces an error into the final result.
So, making an accurate forecast is not yet possible, but the mechanism of the phenomenon is broadly understood by scientists. Stress in the earth's crust reaches its maximum value a few days before the earthquake. Small cracks occur, which are filled with ground water. Trickles of radioactive gas from radon emitting alpha rays also seep through them, and they ionize air molecules. An abnormal electromagnetic field is created. His tension is higher than usual. Therefore, the content of free electrons also becomes different.
NASA scientists are also convinced that the approach of large earthquakes can be predicted by the change in electrical activity in the ionosphere. Exist « a clear correlation between electrical signals in the atmosphere and earthquakes. ” In this case, in the not too distant future, it is possible to create a global earthquake warning system - similar to the one that monitors tsunamis in various parts of the World Ocean. To do this, it is enough to put into orbit a network of satellites that will monitor atmospheric phenomena.
Another curious natural phenomenon. Six days before the strong earthquake in Gujarat (it claimed the lives of about 20 thousand people), satellites recorded an increase in soil temperature in this area (its largest increase was 4 °). The most amazing thing is that this was noted exactly where the elements subsequently struck - along the main fault line. And this has been observed more than once.
Perhaps a similar increase in temperature occurs before each earthquake. As an analysis of information about the temperature of the soil and the lower atmosphere collected by meteorological satellites in regions where earthquakes soon occurred, this thermal anomaly covers a circle with a radius of about 100 kilometers from the epicenter of the disaster. However, such a method still does not allow reliable prediction of the impact of the elements. You can rely on it only if the sky in the zone of the future earthquake remains cloudless all the time, and the earth does not have high vegetation, such as shrubs or forests. This is an ideal method of tracking down the insidious elements, and therefore everywhere where the ideal is far away, the awakening of Seismos will continue to be unexpected. To say that we will soon succeed in accurately predicting the start of an earthquake based on this method is like guessing on coffee grounds.
Ukrainian astrophysicist Vasily Ivchenko proposed another method of forecasting - observation of the upper atmosphere. His work took into account 234 earthquakes that occurred in the 1990s. From the information presented by him it is seen that approximately a hundred kilometers from the surface of the Earth several hours before the impact, an increase in temperature was noted. However, this work does not give hope that a wonderful method will soon appear that will save us from troubles. Study participant Lyudmila Kozak emphasized: “Unfortunately, we were not able to prove that the temperature rises before each earthquake, and, moreover, we cannot even say that whenever the temperature in the upper atmosphere rises, an earthquake will follow” .
Another problem lies in the fact that scientists cannot explain the mechanism of temperature differences. Why does it get warmer when the element prepares to strike? Why is the air warmed high above the ground? Some speculatively talk about the "local greenhouse effect," arguing about the "gases rising above the ground on the eve of the elements." Allegedly, heated gases are squeezed out of the bowels of the planet. They expand, giving rise to a wave, which, having passed the tropopause, reaches the upper layers of the atmosphere, where vortex flows arise - they heat the air. Very foggy and confused.
... It seems that the elements of heaven, earth and water themselves conspired against scientists seeking to understand the mysterious course of earthquakes. Nature does not want to reveal its secrets. Or are some signals telling us exactly what is happening in the bowels of the planet? In a word, can an earthquake be predicted? Scientists themselves call the answer to this question the “holy grail” of seismology. There are many ways leading to this goal. But…
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“The steps of the river terraces - a particularly clear indicator of the tectonic movements of the Urals - allow us to trace in great detail both the long and close history of the rise of the mountains. The generally accepted average growth rate of the Urals is about two millimeters per century. However, in some places the Ural Mountains grow by five or more millimeters per year. Of course, in comparison with actively developing highly seismic mountain systems - the Tien Shan, Pamir, the Caucasus and others - the ancient Urals is in no hurry. There are relatively few earthquakes recorded here. But this is quite enough for an urgent, comprehensive study of modern geological processes of development of the Urals and their impact on human activities. ”
Earthquakes are best known for the devastations they are capable of producing. Destruction of buildings and structures is caused by soil vibrations or giant tidal waves (tsunamis) arising from seismic displacements on the seabed. In this case, the destruction depends on the type of structures that are common in the area of the earthquake. Fatal structures are often lethal for their inhabitants in severe earthquakes, they are very common in rural areas of many seismically active regions of the Earth, an example is the earthquake in Guatemala (1976).
Most of the centers of earthquakes occur in the earth's crust at a depth of 30-40 km below the surface of the Earth. The most active zones in relation to earthquakes are the Pacific belt, which runs along almost the entire coast of the Pacific Ocean (approximately 90% of all earthquakes of the Earth) and the Alpine belt, stretching from Indonesia to the Mediterranean Sea (5-6% of all earthquakes). It is also worth noting the mid-ocean ridges, although earthquakes here are shallow and have a much lower frequency and strength (together with earthquakes inside the plates make up 4-5% of all earthquakes).
Earthquakes can also be caused by landslides and large landslides. Such earthquakes are called landslides; they have a local character and a small force.
Volcanic earthquakes are a type of earthquake in which tremors occur as a result of high stress in the bowels of a volcano. The reason for such earthquakes is lava, volcanic gases. Earthquakes of this type are weak, but last long, many times - weeks and months. Nevertheless, an earthquake of this type does not pose a danger to people. By the way, an earthquake is sometimes the most dangerous natural disaster along with a volcanic eruption.
The cause of the earthquake is the rapid displacement of the lithosphere (lithospheric plates) as a whole at the moment of relaxation (discharge) of the elastic deformation of stressed rocks in the earthquake source.
According to the scientific classification, the depth of the earthquake is divided into 3 groups:
- “Normal” - 33–70 km,
- “Intermediate” - up to 300 km,
- “Deep focus” - over 300 km.
The last group includes an earthquake that occurred on May 24, 2013 in the Sea of Okhotsk, then seismic waves reached many parts of Russia, including Moscow. The depth of this earthquake reached 600 km.
According to Gutenberg and Richter, the depth of the June 29, 1934 earthquake with the epicenter in the Flores Sea was 720 km.