The weak zones of earth's crust which is more prone to earthquakes are called seismic zones. It is also known as fault zones.
In India, the areas most affected or threatened by earthquakes are Kashmir, Western and central Himalayas, the whole of North-east, Rann of Kutch, Rajasthan and Indoh gangetic plane. Some areas of South India is also prone to earth-quakes.
SEISMOGRAPH: THE EARTHQUAKE MEASURING INSTRUMENT.
Seismograph is an instrument which measures and records the magnitude of an earthquake in terms of the shock waves it produces.
A seismograph consists of a heavyweight like a heavy metal ball suspended from a support with the help of a strong wire. The support is attached to the base of the seismograph and the base is rigidly fixed to a solid rock on the surface of the earth. A pen is attached to the the lower end of the hanging heavyweight. It is used to draw graphs on the graph paper which is wrapped around a rotating drum. When earthquake occurs the pen draws graphs on the graphsheets due to the oscillation of the heavy object. From this graph we can measure earthquakes.
FOCUS AND EPICENTER OF EARTHQUAKE:
The place inside the earth's crust where the earthquake is generated, is called 'focus' of the earthquake.
The point on earth's surface directly above the focus is called epicenter.
MAGNITUDE OF EARTHQUAKE AND RICHTER SCALE:
The magnitude or intensity of an earthquake is expressed on the Richter Scale.
In a Richter scale 1 to 12 numbers are assigned to express the magnitude of an earthquake.
Suppose the magnitude of an earthquake is 3 on the Richter scale, and magnitude of another Earthquake is 4 on the Richter scale, then the second earthquake is 10 times more intense than first earthquake.
The magnitude of earthquake having 4 in Richter Scale is ten times more than the magnitude of the Earthquake having 3 on the Richter scale.
The Earthquakes having magnitudes higher than 7 on the Richter Scale are called destructive Earthquake.
PROTECTION AGAINST EARTHQUAKE:
Earthquakes are highly destructive and it cannot be predicted. Therefore, we should always take some precaution against earthquake.
1. All the houses and other buildings in seismic zones should be designed and constructed in such a way that they can with stand measure earthquake tremors.
2. In highly systemic areas the use of mud and timber for building houses is better than using heavy construction materials.
3. The cupboards and shelves should be fixed to the world's so that they do not fall easily when shaking occurs during an earthquake. Glass bottles should not be placed on high shelves and heavy objects should be placed low to the ground.
4. The objects such as heavy mirrors, photo frames, wall clocks and water heaters should be mounted securely on the world at such places in the house that they do not fall on the people in the house in the event of an earthquake.
5. All buildings should have fire fighting equipment in working order because some buildings may catch fire during an earthquake due to electric short circuits.
PRECAUTIONS TAKEN WHEN EARTHQUAKE OCCURS:
A. If we are at home when an earthquake occurs.
We should take the following precautions.
1. We should take shelter under a study table for a kitchen counter and stay there till the shaking due to earthquake stops and we should cover our head with hands.
2. We should stay away from tall and heavy objects so that if they topple they may not for on us. We should also stay away from glass windows that may shatter due to vibrations.
3. If we are in bed, we should just move on the bed to be close to a wall but not get up from the bed. We should protect our head with a pillow.
B. If we are outdoors when an earthquake occurs.
We should take the following precautions.
1. We should stay at a clear spot away from buildings, trees and overhead power lines etc. We should also seat on the ground.
2. If we are in a car or bus, we should not come out of it. The car or bus should be driven slowly to a clear spot away from buildings, trees and overhead electric wires etc. We should not come out of the vehicle till the tremors stop.
No comments:
Post a Comment