The basic questions concerning an earthquake are: What is an earthquake? What happens when it occurs? What is the cause of an earthquake? what can we do to minimize its effect?
I will now try to get some explanations/answers to these question.
An earthquake is a sudden tremor or movement of earth's crust which lasts for a very short time. It originate naturally at or below the surface of the earth. We often hear about the earthquake in news only once in a while, even though earthquake occurs all time, all over the earth. There are about 800 of them everyday. This is because the vast majority of these quakes are very week. The are not even noticed. Major earthquakes are very much less frequent but are most destructive. Major earthquakes usually do not occur alone; when one such earthquake happens, there is usually another one at a nearby location. Sometime, an earthquake also has foreshocks. These are smaller earthquakes that happen in the same place before the larger earthquake follows. As at present, Scientist cannot predict accurately that a given earthquake is a foreshock and is likely to be followed by a larger earthquake.
Effects of an earthquake
Earthquake produces various damaging effect in the areas the act upon. The list of some of the main effects caused by earthquakes are given below:
1. Earthquake causes damage to the building, bridges, dams.
2. Earthquake in many cases, can cause great loss of life.
3. Earthquake can also cause floods and landslides. Landslides, triggered by earthquake, often cause more destruction than the earthquake themselves.
4. If the earthquake happens to be beneath the ocean floor, they can lead to a tsunami.
Causes of earthquake
It is known that earthquake are caused by disturbances deep down inside the uppermost layer of the earth. The outermost layer of the earth is not in a single piece but is broken into number of plates known as lithospheric plates or tectonic plates. It may surprise you, but these plates are moving around very slowly just a few millimetres every year due to the movement of the molten magma inside the earth. The movements of these plates cause changes on the surface of the earth. The movements of these plates cause changes on the surface of the earth and can cause an earthquake.
When the plates try to slide past each other. The boundaries of the plates get interlocked due to friction. The rest of the plates keeps moving. This cause a tension to build up in the plates. When the force of moving plates overcomes the friction of the edges, all the stored energy gets released. The earth shakes at this point. The vibration at the point. The energy gives rise to shock or seismic waves very much like ripples in a pond, when a stone is thrown into it. These shock waves shake the earth as they move outward through it. When the waves reach the surface of the earth, they shake the ground and anything on it.
Scientists call the origin of the earthquake, the point at which tension is released as its focus. Since this is often deep below the surface of earth and difficult to map, its location is specified by the point on the surface of earth, directly above the focus. This point on the surface of earth is known as epicenter of the earthquake. The shock waves travel outward from the epicenter. Greatest damage usually happens closest to the epicenter. The strength of the earthquake decreases away from the epicenter. The whole phenomenon may last for a just a few seconds.
Predicting an earthquake
We now know about the causes of an earthquake. But to predict when, and where, the next earthquake might occur is a very difficult task. Attempts at predicting when and where earthquakes will occur have met with some success in recent years. Geologists also have been able to use instruments such as seismometers to find out the sources of seismic waves. They are also investigating other potential clues like tilting of building and change in the earth's magnetic field.
Measuring an earthquake
We can realize that the destruction caused by an earthquake depends on many factors. One major factor is its intensity. Geologists usually express the intensity of an earthquake in terms of a magnitude on a scale known as the Richter Scale. The Richter scale, named after Dr. Charles F. Richter, is the scale used for measuring the strength of an earthquake, in terms of the amplitude of its seismic waves.
- This scale is not a simple scale.
- On this scale, an increase of two in the magnitude means 100 times more destructive energy.
Protection against earthquake
The earthquake strike suddenly, violently without warning at nay time of the day or night. If an earthquake occurs in a populated area, it can cause death and injuries and property loss. It is, therefore, important that we identify the potential hazards before hand and take necessary precautions to protect ourselves as best as we can. People living in seismic zones where the earthquake are most likely to occur, have to be specially prepared.
1. All the building in seismic zones need be designed so that they can withstand major tremors. It is advisable to make the structure simple so that it is 'Quake Safe'.
2. Since some building may catch fire, it is necessary that all the building have their fire fighting equipment in order.
3. Since some buildings may catch fire, it is necessary that all the building have their fire fighting in order.
4. Safer places indoors, as well as outdoors, must be clearly identified.
5. An emergency communication plan should be made available.
6. Disaster management supplies (like flashlights, first aid box etc.) should be available on hand.
Safety precautions during earthquake
For a person present inside of a building:
1. Take shelter under a table and stay there till the shaking stops.
2. Stay away from tall and heavy objects that may fall on you.
3. Do not get up, if you are in bed. Protect your head with pillows.
4. Stay indoor until shaking stops and it is safe to move outside. Most of injuries occur when people, inside the building, attempts to move to a different location within the building or try to leave it.
For a person caught outside in the open:
1. Find a clear spot, away from buildings, trees, bridges and overhead power lines. Drop to the ground.
2. Do not come out, if in a moving vehicle. Drive slowly to a clear spot and stay inside. Come out only when the tremors stop.
Safety precautions after the earthquake
1. Stay calm for a while. Expect after shocks. These shocks can cause additional damage.
2. Beware of possible tsunami, if you live in coastal area.
3. Carefully inspect utilities/supplies.
4. Use telephones only in emergency.
5. Stay away from damaged areas.
6. Help the injured ones.