What is an earthquake?
Earthquake is sudden shaking of outer layer of earth surface(Lithosphere). This is a natural calamity on which there is no control of human being.It comes without information and causes loss of life and materials according to intensity.
Causes of Earthquakes:
To know the reason of earthquake we have to understand the structure of earth surface.Our earth is made up of mainly four layers.
These layers are inner core,outer core,mantle and crust.Outer core is molten lava and in liquid state.Crust and upper mantle is called lithosphere.this is 50-100 km thick layer.These layers are divided in seven parts.These parts are called Tectonic plates.These plates moves very slowly from their place.
When these tectonics plates slip past one another,friction sometime causes these plates to stuck together.Plates are continued to move but their edges are stuck with the other plate's edges. Pressure is developed between the plates.Kinetic energy of plates is saved in the form of potential energy till a threshold point reaches and plates suddenly moves.Sudden movement of plates releases stored energy abruptly and vibrations occur. These vibrations travel toward the earth surface.These vibrations are called seismic waves.
The plane formed between the plates where they slip one another is called fault line.
The point inside the earth where pressure is released is called focus or hypocentre.
The point on the Earth's surface above the focus is called epicentre.
How seismic waves travel?
Mainly there are two types of seismic waves.
1.Body waves
2.Surface waves
Body waves travel through the inner layers of the earth and reaches first on the earth surface. Body waves have higher frequency than surface wave.
Body waves are further categorized into
1. Primary waves or P wave:P waves are faster than S wave and first to measured by seismograph.
Speed: 1-14 km/sec.
These are compression waves or push-pull waves and moves in parallel and straight.
They can travel travel through any kind of material i.e all the three mediums solids, liquids and gases.
2.Secondary wave or S wave: These waves are slower than S wave and reaches after the P wave on e earth surface.
Speed: 1-8 km/sec.
These are transverse wave like sine waves.when the waves travel forward particle travel up and down.They can only travel through solid medium.
Surface waves:
surface waves move along the surface of the earth and reaches later than body waves. These waves have lower frequencies.Due to travelling near the surface surface waves are entirely responsible for the damages and destruction associated with the earthquakes.
How are Earthquakes recorded?
The instrument used for recording earthquakes is seismograph and the recording done by seismograph is called seismogram.
The strength or magnitude of the earthquake is measured using Richter Scale.Richter is numbered 0-10. Richter scale is a base 10 logarithmic scale.
Magnitude Severity
1-2.9 Generally not felt,micro
3-3.9 felt by many people,no damage
4-4.9 felt by all,minor breakage
5-5.9 some damage to weak structures
6-6.9 moderate damage,earthquake resistant building survive with slight damage
7-7.9 severe damage,felt across long distance
8 and higher major damage,felt in very large area.
Safety from earthquakes: Does and Dont's
Awareness about earthquakes is the protection from earthquakes.
If you are indoor:
1. Drop to the ground and take cover under the table and other piece of furniture untill the shaking stops.If there is no table ,cover your face and head with your arms and crouch in the corner of a room.
2.Protect yourself by staying under the bed,back of the door,corner of a room.
3.stay away from glass window,anything that can fall.
4.If you are in bed,cover your head with pillow unless you are under a heavy light fixture that can fall.
If you are outdoor:
1. Move away from buildings,trees,street lights and utility wires.
2.If you are in a moving vehicle,stop and stay in your vehicle.
If trapped under Debris:
1. Do not light a match.
2.Tap on a wall or pipe so that rescuer can locate you.
3.Use a whistle if it available.
4. Shout only as a last resort behause you have to inhale dangerous gases and dust.
Then why red cloths are seen to bulls in game to make them angry.Actually bulls attack not seeing red colour but waving of the cloth by metador. It is waving that cause them to charge not the colour of the cloth.They feel threat from moving objects.
