On July 23, the fourth earthquake in a day occurred in Iran, and the number of victims reached 287. A day earlier, tremors of magnitude 5.2 were registered in Chile. In general, for 7 months of 2018, 6881 earthquakes occurred on Earth, which took 227 human lives. But why haven't scientists learned to predict these cataclysms? Understood Realist.
How seismically hazardous zones are determined
Lithospheric plates are in constant motion. Colliding and stretching, they increase the tension in rocks ah, which leads to their rapid rupture - an earthquake. The focus (hypocenter) of an earthquake is located in the bowels of the earth, and the epicenter is its projection on the surface.
The strength of earthquakes is measured on a scale of destruction in points (from 1 to 12), as well as magnitude - a dimensionless value that reflects the released energy of elastic vibrations (from 1 to 9.5 on the Richter scale).
The easiest way for science is to identify seismically hazardous zones and long-term earthquake prediction for the next 10-15 years. To do this, researchers analyze the cyclicity of the activation of the seismotectonic process: there is no reason to believe that in the next few hundred years the Earth will begin to behave differently than in a similar period of time in the past.
Can earthquakes be predicted?
No, at least not with sufficient accuracy to allow for the planning of population evacuation programs. While most earthquakes occur in predictable locations along well-known geological faults, the reliability of short-term forecasts leaves much to be desired.
“We have models that show that in Southern California the risk of earthquakes of magnitude 7.5 and above in the next 30 years is 38%. If these models are used to calculate the probability of earthquakes for the next week, the probability drops to about 0.02%,” says Thomas Jordan, director of the Southern California Earthquake Center.
This risk is quite small, but still not zero, and since the San Andreas transform fault runs through the state of California, local schools regularly conduct exercises to prepare for a large earthquake.
Why are large earthquakes so difficult to predict?
Reliable predictions require the identification of signals that would indicate an approaching large earthquake. Such signals should be typical only for large earthquakes: weak and moderate shocks of magnitude up to 5 can cause hanging objects to sway, glass to rattle or plaster to fall, which does not require the evacuation of the population. However, in 5–10% of cases, such shocks turn out to be foreshocks that precede stronger earthquakes. According to statistics, foreshock activity is typical for 40% of medium and 70% of large earthquakes.
Seismologists have not yet been able to isolate specific events that regularly occur just before large earthquakes.
Today, a wide range of potential earthquake predictors has been studied - from an increase in the concentration of radon in the air and unusual animal behavior to deformation earth's surface and changes in groundwater levels. But these anomalies are common: each of them can occur even before the weakest shocks.
Why people are not evacuated at the slightest risk of a large earthquake
The main reason is the high probability of false alarms. So, in 1975, in Haicheng (China), seismologists recorded more frequent weak earthquakes and announced a general alarm on February 4 at 2 pm. After 5 hours and 36 minutes, an earthquake of more than 7 points occurred in the city, many buildings were destroyed, but thanks to timely evacuation, the cataclysm cost almost no casualties.
Unfortunately, such successful forecasts could not be repeated in the future: seismologists predicted several large earthquakes that did not take place, and the shutdown of enterprises and the evacuation of the population only resulted in economic losses.
How Earthquake Early Warning Systems Work
Japan has the best earthquake early warning system today. The country is literally “littered” with stations that, using sensitive equipment, register seismic waves, identify potential foreshocks and transmit information to the Meteorological Agency, which, in turn, immediately transmits it to TV, the Internet and mobile phones of citizens. So, by the time the second seismic wave arrives, the population has already been warned about the epicenter of the earthquake, its magnitude and the time of the second wave.
Despite technological advances, even the Japanese warning system goes off after a natural disaster has occurred. But until researchers thoroughly study the physical processes associated with earthquakes, one cannot count on more. Residents of seismically active zones can only hope that seismometers will become more sensitive, and satellite observation will help speed up the forecast time.
In a technical sense, an earthquake is defined as an unforeseen release of energy in the earth's crust, which leads to the formation of seismic waves. Earthquakes are also understood as tremors or shudders of the earth's crust. Many people wonder if it is possible to predict earthquakes, but before answering this question, it is worthwhile to understand the following: earthquakes are a completely natural process that humanity cannot control today.
Today, scientists are only able to identify individual places on the planet where there is a possibility of major earthquakes. However, the time, place and absolute probability of an earthquake modern science currently unable to determine. Perhaps in the future, scientists will be able to predict earthquakes the way meteorologists can predict the weather, but so far these are just dreams and hopes for the future.
Conjectures and hypotheses
Researchers of seismic phenomena have modern equipment at their disposal, which allows them to make certain guesses about the possibility of an earthquake at one point or another on the planet. However, these are just guesses and hypotheses, and there is no guarantee that they can be confirmed in reality.
Analyzing the history of earthquakes in a particular region, scientists are able to build certain hypotheses and make assumptions about the possibility of repetition of tremors in this place.
Possessing the results of research, scientists using special equipment and modern technologies establish points of increasing pressure in the underground crust and determine the lines of tectonic disturbances. Only after a rigorous analysis of these data, experts can very roughly assume the possibility of an earthquake at a given point. Such predictions are very, very unreliable.
What has been achieved
Scientists have made significant progress in predicting the occurrence of additional tremors that may follow after the main initial earthquake, such phenomena are sometimes called aftershocks (from the English aftershock).
Per last years many of these predictions turned out to be 100% correct. Such forecasts are based, first of all, on a deep and thorough analysis and study of charts and common features, following the first earthquake, repeated tremors, while the basis of such studies is the study of the lines of tectonic disturbance identified during or after the first earthquake.
To be sure, earthquake research today is far ahead of what the industry was like a few decades ago. Technology development and modern methods research may soon help scientists move even further.
Researchers believe that a key link in the theory of studying earthquakes and the possibility of predicting them is a clear understanding of the relationship between magnetic and electric charges rocks and the occurrence of an earthquake as a phenomenon.
Experts consider the study of the electromagnetic charge of rocks of fundamental importance, since it was found that in a very short time before earthquakes, the properties of electromagnetic fields change to a certain extent. It is quite obvious that the key to unraveling the occurrence of earthquakes and the possibility of their successful prediction lies in a detailed study of electromagnetic fields and the patterns of their change. In this area, scientists continue to conduct research, but, unfortunately, today it is almost impossible to predict the occurrence of an earthquake at one point or another on the planet with a significant degree of probability.
The earth has one unfortunate property: it sometimes slips out from under your feet, and this is not always associated with the results of a cheerful party in a friendly circle. From the shaking of the soil, the asphalt stands on end, the houses collapse. What is there at home? catastrophic earthquakes can uplift or destroy mountains, drain lakes, turn rivers. Residents of houses, mountains and coasts in such situations have only one thing left: to try to survive as much as possible.
People have been confronted with the riot of the earth's firmament since about the time when they descended to this firmament from the trees. Apparently, the first attempts to explain the nature of earthquakes also date back to the beginning of the human era, in which underground gods, demons and other pseudonyms of tectonic movements appear abundantly. As our ancestors acquired permanent dwellings with fortresses and chicken coops attached to them, the damage from shaking the ground beneath them became greater, and the desire to appease Vulcan, or at least predict his disfavour, became stronger.
However, different countries in ancient times they were shaken by various entities. Japanese version assigns a leading role to giant catfish living underground, which sometimes move. In March 2011, another fish riot led to a massive earthquake and tsunami.
Scheme of tsunami propagation in the water area Pacific Ocean. The painting shows in color the height of the waves diverging in different directions, generated by an earthquake near Japan. Recall that the earthquake on March 11 brought down a tsunami wave on the coast of Japan, which led to the death of at least 20 thousand people, extensive destruction and the transformation of the word "Fukushima" into a synonym for Chernobyl. Tsunami response requires great speed. Ocean waves are measured in kilometers per hour, and seismic waves in kilometers per second. Due to this, there is a margin of time of 10-15 minutes, during which it is necessary to notify the inhabitants of the threatened territory.
Unsteady firmament
The earth's crust is in very slow but continuous motion. Huge blocks push against each other and deform. When the stresses exceed the tensile strength, the deformation becomes inelastic - the earth's firmament breaks, and the layers are displaced along the fault with elastic recoil. This theory was first proposed almost a hundred years ago by the American geophysicist Harry Reid, who studied the 1906 earthquake that almost completely destroyed San Francisco. Since then, scientists have proposed many theories that detail the course of events in different ways, but the fundamental principle has remained broadly the same.
The depth of the sea is variable. The arrival of a tsunami is often preceded by a retreat of water from the shore. Elastic deformations of the earth's crust preceding an earthquake leave the water in place, but the depth of the bottom relative to sea level often changes. Monitoring of the sea depth is carried out by a network of special instruments - tide gauges, installed both on the coast and at a distance from the coast.
The variety of versions, alas, does not increase the amount of knowledge. It is known that the focus (scientifically - the hypocenter) of an earthquake is an extended area in which the destruction of rocks occurs with the release of energy. Its volumes are directly related to the size of the hypocenter - the larger it is, the stronger the shaking. The centers of destructive earthquakes extend for tens and hundreds of kilometers. Thus, the source of the Kamchatka earthquake of 1952 had a length of about 500 km, and the Sumatran earthquake, which caused the worst in December 2004, modern history tsunami - at least 1300 km.
The dimensions of the hypocenter depend not only on the stresses accumulated in it, but also on the physical strength of the rocks. Each individual layer that is in the destruction zone can either crack, increasing the scale of the event, or resist. The final result ultimately turns out to be dependent on many factors invisible from the surface.
Tectonics in pictures. Collision of lithospheric plates leads to their deformation and stress accumulation.
seismic climate
Seismic zoning of a territory makes it possible to predict the strength of tremors possible in a given place, even if without specifying the exact place and time. The resulting map can be compared with the climatic one, but instead of the atmospheric climate, it displays a seismic one - an assessment of the earthquake strength possible in a given place.
The initial information is data on seismic activity in the past. Unfortunately, the history of instrumental observations of seismic processes is a little over a hundred years old, and even less in many regions. Collecting data from historical sources: descriptions of even ancient authors are usually enough to determine the magnitude of an earthquake, since the corresponding scales are built on the basis of everyday consequences - the destruction of buildings, people's reactions, etc. But this, of course, is not enough - humanity is still too young. If a region has not had a magnitude 10 earthquake in the last couple of thousand years, this does not mean that it will not occur there next year. While we are talking about ordinary low-rise construction, one can put up with the risk of this level, but the placement of nuclear power plants, oil pipelines and other potentially hazardous facilities requires clearly greater accuracy.
Is an earthquake possible in Seoul? The end of 1999 was marked by considerable seismic activity. Devastating earthquakes have occurred in Turkey and Taiwan, Greece and Mexico. There is nothing surprising in the fact that now, after all these catastrophes, Koreans have also begun to worry about whether Korea might also become a victim of a seismic cataclysm. On the whole, the Korean Peninsula is an area of rather weak seismic activity. Its southeastern tip is only a few hundred kilometers from the Pacific Rift. This fault is a huge arc that starts in Alaska and goes further south through the Kuriles, Japan and Taiwan, to Indonesia and New Zealand. This fault is one of the most seismically unstable regions of the planet. It is constantly shaken by earthquakes, and most of the planet's active volcanoes are concentrated there. On the other hand, to the east of the Korean Peninsula, on the opposite coast of the Yellow Sea, lies another seismically active zone. It is relatively small, but fraught with considerable trouble (not least because it is located under the most densely populated regions of northern China). It was here, relatively close to Beijing, that the most catastrophic earthquake of our century occurred in July 1976, killing 220,000 people. However, despite such a dangerous neighborhood, from the point of view of seismologists, the Korean Peninsula is one of the relatively stable areas. Earthquakes occur here from time to time, but still remain rare. At one time, in the twenties, this circumstance even forced the Japanese government to seriously discuss the issue of transferring the capital of the Japanese Empire to Seoul from seismically unsafe (especially with the then construction technology) Tokyo. However, the question arises: is it possible to consider that Korea is absolutely safe? Alas, it is not. In ancient Korean chronicles, there are references to very serious earthquakes, accompanied by destruction and loss of life. So, in 779 in the Korean capital, which was then located in the city of Gyeongju, in the southeast of the peninsula, "the earth shook, many houses collapsed, and about a hundred people died." In 1455 in Seoul, then already the capital of the country, "buildings collapsed, and many people died under the ruins." Korean scientists, relying on chronicles, traces of damage on ancient buildings and geological data, have established that over the past two millennia, about 40 earthquakes of magnitude 7 or more have occurred in Korea. This is not a very large figure by the standards of, say, Japan or Turkey, but still this figure gives cause for concern. In addition, recent years have seen a suspicious increase in seismic activity. If in the 1980s about 10-15 micro-earthquakes per year were recorded in Korea, then in the 1990s their number approximately doubled. In 1996, 39 earthquakes were recorded in Korea, in 1998 - 32. This year seems to be a record one, since in its first nine months, Korean seismologists registered 34 earthquakes. This, of course, is about small earthquakes that people do not notice and can only be recorded with special instruments. Nevertheless, the growth of seismic activity in Korea is obvious. Of particular concern is the fact that the largest center of seismic activity is located in the Seoul region, that is, where almost half of the country's population is now concentrated. There are also two less serious seismic sources in Korea: in the southeast, in the Daegu and Gyeongju regions, and in the north, near the North Korean capital of Pyongyang. Korean seismologists estimate at 57% the probability that in the next 10 years a large (about 6 points) earthquake will occur in the Seoul region, roughly corresponding in strength to the recent devastating earthquakes in Greece and Taiwan. For Pyongyang and Daegu, this probability is 35% and 29%, respectively. A probability of 57% is by no means small, so measures are now being taken in Korea to prepare for a possible earthquake. In particular, after 1988, all houses in the country are built in such a way as to withstand a five-magnitude earthquake without damage. Schools and public buildings are subject to stricter regulations. How effective are all these measures? To answer this important question, Korean seismologists and engineers recently ran simulations of how a hypothetical 6.3 magnitude earthquake would affect an area in central Seoul. According to geologists, two thousand years ago (more precisely, in 89 AD), an earthquake of approximately this magnitude already occurred on the territory of the current Korean capital. An area of 1 square kilometer, where there are 780 buildings for various purposes. The analysis showed that about a third of the buildings are likely to be heavily damaged by an earthquake. At the same time, the most vulnerable were not multi-storey residential complexes built of reinforced concrete, but brick houses 2-4 floors high. In addition, who, if not us, residents of Russia and the CIS, should not know that any, the most wonderful and most thoughtful standards mean nothing if they are simply ignored by builders. This, by the way, was the case in Turkey, where most of the houses were built in violation of existing norms. It is clear that it was profitable for entrepreneurs to "save" on building materials, while the Turkish bureaucracy turned out to be inefficient and corrupt, and was ready to turn a blind eye to gross violations of instructions. Be that as it may, the recent catastrophes in Turkey and Greece have forced the Koreans to think again about the problems of seismic safety. After all, as the Korean press recalls, the costs of preventing destruction are 10-20 times less than the amounts that then have to be spent on restoring the destroyed ...
The question of where an earthquake can occur is relatively easy to answer. For a long time there are seismic maps on which seismically active zones are marked. the globe(Fig. 17). These are the parts of the earth's crust where tectonic movements occur especially frequently.
It should be noted that earthquake epicenters are localized in very narrow zones, which, according to some scientists, determine the interacting edges. lithospheric plates. There are three main seismic belts - Pacific, Mediterranean and Atlantic. About 68% of all earthquakes occur in the first of them. It includes the Pacific coast of America and Asia and through the island system reaches the coast of Australia and New Zealand. The Mediterranean belt stretches in a latitudinal direction - from the Cape Verde Islands across the Mediterranean coast, south Soviet Union to Central China, the Himalayas and Indonesia. Finally, the Atlantic Belt runs along the entire underwater Mid-Atlantic Ridge from Spitsbergen and Iceland to Bouvet Island.
Rice. 17. Scheme of location of seismically active zones of the globe. 1, 2, 3 - shallow, intermediate and deep points, respectively.
On the territory of the Soviet Union, about 3 million square kilometers are occupied by seismically dangerous regions, where earthquakes of magnitude 7 or more are possible. These are some areas of Central Asia, the Baikal region, the Kamchatka-Kuril ridge. The southern part of Crimea is seismically active, where the 8-magnitude Yalta earthquake of 1927 has not yet been forgotten. The regions of Armenia, where in 1968 a strong 8-magnitude earthquake also occurred, are no less active.
Earthquakes are possible in all seismically active zones, in other places they are unlikely, although not excluded: some Muscovites may remember how a 3-magnitude earthquake occurred in our capital in November 1940.
It is relatively easy to predict where an earthquake will occur. It is much more difficult to say when it will happen. It has been noticed that before an earthquake, the slope of the earth's surface, measured by special instruments (tiltmeters), begins to change rapidly, and in different directions. There is a "storm of tilts", which can serve as one of the harbingers of an earthquake. Another way to predict is to listen to the "whisper" of rocks, those underground noises that appear before an earthquake and increase as it approaches. Highly sensitive devices register the amplification of the local electric field- the result of rock compression before an earthquake. If on the coast, after tremors, the water level in the ocean changes dramatically, then a tsunami must be expected.
