Scientists from 6 century B.C. to 19 century A.D. proposed water or air theory of earthquakes. It means that inside the Earth there are huge shallow areas where air and water circulate. When they move too strongly, the earth’s surface shakes. In 18-19 A.D. there was a hypothesis that earthquakes are caused by the volcano eruptions.
Some scientists have an idea that moon tides can cause an earthquake in a seismically active area. The moon is known to have tidemaking power
40 % stronger when the moon is at the closest distance from the Earth than it is far from our planet. This power causes the strain and deformation of the Earth's crust.
A convincing example of the connection between underground and space events, as American astrophysicists S. Kilston and L. Knopoff think, is frequent earthquakes in California. The scientists proved that the moon gravity power in the full phase causes tension in the earth's crust. All strong (more 6 balls) earthquakes, which occured in California after 1933, were connected with the full and new moon phases, the time of the day (6 am or pm) and the moon positin in the sky.
Theory of crust plates
The most popular explanation of the reasons causing earthquake is so-called «theory of crust plates». The essence of this theory is that habitual for us firm and rigid terrestrial crust - actually represents a shaky coverlet from a number of blocks - plates, similar huge ice-floes, restricted in the frozen sea. The huge platforms slowly float , move in the astenosphere - the upper layer of the mantle. On some plates or platforms, continents are located. They drift together with a platform, changing their location. Where the vast, rigid drifting plates adjoin, rub against each other and collide, the mountain ranges rise, the volcanoes erupt, earthquakes happen. The first man who scientifically explained and proved this hypothesis was a German scientist Ŕlfred Wegener (1880 - 1930).
A.L. Chizhevsky assumed that the fatal role in life of the Earth is played by so-called “parade of planets”, when they settle down approximately in one plane and approximately on one line from the Earth. Their gravitational influences on the Earth are united, therefore on our planet happens natural accidents: earthquakes, eruptions of volcanoes, great floods, etc. In the twentieth century “the parade of planets” was observed several times, but none of the natural phenomena occured.
The scientist consistently protected another idea about influence of solar activity cycles on terrestrial processes. The author built a system of cycles appropriate to maxima of solar radiations.
A.L. Chizhevsky made the conclusion that the world processes depend on cycles that are equal to about 11 years, and synchronic to the sun spot making activity.
Technogene earthquakes can be caused by underground nuclear tests, water reservoir filling, oil and gas extracting with the technique of liquid delivery into peeps, explosions, etc. Weaker earthquakes occur when the arch of the caves fall.
At the end of the XX century, the world-wide technogene human activity caused artrificial seismic activity, which occur due to nuclear explosions. Sometimes the building of water resevoirs provoke an earthquake. Such a disaster took place in India, when the consruction of the water resevoir caused an 8 ball earthquake killing 177 people.