O’zbekiston respublikasi oliy va o’rta maxsus ta’lim vazirligi mirzo ulug’bek nomidagi o’zbekiston milliy universiteti

Note

* in spite of the fact that... — haqiqatga qaramasdan
XVI. Answer the following questions ofter reading the text given below

1. 
   What do you call an earthquake?
   
2. 
   What facts did scientists establish after careful study of earthquakes?
   
3. 
   What varieties of earthquake motion do you know?
   

EARTHQUAKES

Earthquakes are shakings of the earth's crust, of degrees varying in intensity from scarcely perceptible tremors to violent agitations that overthrow buildings and open huge fissures in the ground. They may either accompany volcanic eruptions, or they may occur independently of such eruptions. An earthquake is sometimes called a seismic throb or shock. During severe earthquakes considerable areas are permanently raised or lowered. During an earthquake in South America, in 1835, the entire coast line of Chili and Patagonia was elevated from 2 to 10 feet above the ocean level. During an earthquake, in 1819, near the mouth of the Indus, a track some 2000 square miles in area sunk and was converted into a salt lagoon, while a much larger area was elevated some 10 feet.

Many years ago scientists after careful study of earthquakes established the following facts:

1. 
   The place or origin of the shock is situated not far below the earth's surface, but is near the surface, probably, never deeper than thirty miles and often much less.
   
2. 
   The area of disturbance depends not only on the energy of shock, but also on the depth of its origin below the surface: the deeper the origin, the greater the area of disturbance.
   
3. 
   The direction of the motion at the surface is nearly upward over the origin, and more inclined as the disturbance from the origin increases.
   
4. 
   The shape of the area of the disturbance depends on the nature of the material through which the wave is moving. If these arc of nearly uniform elasticity in all directions, the area is nearly circular; if more elastic in some directions than in other the area is irregular in shape.
   

There are three varieties of earthquake motion:

1. 
   Explosive — these are attended by a violoent motion directly upward. During such shocks the crust is broken, and bodies are thrown upward in the air.
   
2. 
   Wave-like*, or horisontally progressive, like waves in water. Here the area of disturbance is great.
   
3. 
   Rotary, or those attended by a whirling motion of the crust. During an earthquake that happened in Chili the ground was so shifted thai three great palm trees were twisted around one another like willow wands.