Every year several hundreds of thousands of earthquakes occur on the globe, and about a hundred of them are destructive, causing death to people and entire cities. Among the most terrible earthquakes of the outgoing twentieth century is the earthquake in China in 1920, which claimed the lives of more than 200 thousand people, and in Japan in 1923, which killed more than 100 thousand people. Scientific and technological progress has been powerless in the face of a formidable disaster. More than fifty years later, hundreds of thousands of people continue to die in earthquakes: in 1976, 250,000 people died in the Tian Shan earthquake. Then there were terrible earthquakes in Italy, Japan, Iran, the United States (in California) and we have - on the territory of the former USSR: in 1989 in Spitak and in 1995 in Neftegorsk. More recently, in 1999, the disaster struck and buried about 100,000 people under the rubble of their own homes during three terrible earthquakes in Turkey.
- The northern end of the Trans-Caucasus transverse uplift is located on the territory of Russia - Stavropol and Krasnodar regions, that is, in the area of Mineralnye Vody and on the Stavropol vault. Weak earthquakes of two or three points in the area of Mineralnye Vody are a common phenomenon. Stronger earthquakes occur here once every five years on average. At the beginning of the 90s, rather strong earthquakes with intensity of three or four points were registered in the western part of Krasnodar Territory - in Lazarevsky district and in the Black Sea depression. And in November 1991 a similar earthquake was felt in the city of Tuapse.
- Is it possible to predict earthquakes? Scientists have been looking for an answer to this question for many years. Thousands of seismological stations, which have tightly enveloped the Earth, watch the breath of our planet, and the whole army of seismologists and geophysicists, armed with instruments and theories, try to predict these terrible natural disasters.
- Earth's bowels are never calm. Processes in them occurring, cause movements of the Earth's crust. Under their influence, the surface of the planet is deformed: it rises and falls, stretches and shrinks, it forms giant cracks. A dense network of cracks (faults) covers the entire Earth, breaking it into large and small areas _ blocks. Individual blocks can move along the faults relative to each other. Thus, the Earth's crust is _inhomogeneous material. Deformations in it accumulate gradually, leading to local development of cracks.
- To be able to predict an earthquake, it is necessary to know how it occurs. The basis of modern ideas about the origin of an earthquake is the position of fracture mechanics. According to the approach of the founder of this science, Griffiths, at some point, the crack loses its stability and begins to spread avalanche-like. In the heterogeneous material before the formation of a large crack, there are various phenomena, precursors to this process. At this stage, the increase in tension in the area of the gap and its length for some reason does not lead to a violation of the stability of the system. The intensity of precursors decreases with time. Stage of instability - avalanche-like propagation of the crack appears after the reduction or even complete disappearance of precursors.
- If we apply the positions of fracture mechanics to the process of earthquakes, we can say that an earthquake is an avalanche-like spread of a crack in an inhomogeneous material - the Earth's crust. Therefore, as in the case of a material, this process is preceded by its precursors, and immediately before a strong earthquake, they must disappear completely or almost completely. It is this feature that is most often used in earthquake prediction.
- The prediction of earthquakes is also facilitated by the fact that the avalanche-like formation of cracks occurs only at seismogenic faults, where they have already occurred many times before. So, observations and measurements for forecasting purposes are carried out in certain areas according to the developed maps of seismic zoning. Such maps contain information about the origin of earthquakes, their intensity, recurrence periods, etc.
- Earthquake prediction is usually done in three stages. Firstly, possible seismically dangerous zones for the next 10-15 years are identified, then the medium-term forecast is made - for 1-5 years, and if the probability of an earthquake in a given place is high, the short-term forecast is made.
Nevertheless, scientists have to admit that the main task of seismology has not yet been accomplished. We can only talk about trends in the development of the seismic situation, but the rare accurate forecasts inspire hope that in the near future people will learn to meet with dignity one of the most formidable manifestations of the force of nature.