What is earthquake and it's effect?

Earth quake

An earthquake is the result of a sudden release of energy in the earth’s crust that creates seismic waves.

The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

Earthquakes are measured using observation from seismometers.

The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe.                               

The most recent large earthquake of magnitude 9.0 or large was a 9.0 magnitude earthquake in japan In 2011(as of march 2011),and it was the Japanese earthquake since records began.

One of the most devastating earthquake in recorded history occurred on 23 January 1556 in the Shaanxi province, China,Killing more than 830,000 people.

Fault or fault pane : the  surface where when two block of the earth suddenly slip past one another   

hypocenter : The location below the earth’s surface where the earthquake starts

.Epicenter : The location on the surface of the earth directly above the hypocenter 

  Types of earthquake

          There are four types of earthquakes.

1.    Tectonic earthquakes

2.    Volcanic earthquakes

3.    Collapse earthquakes

4.    Explosion earthquakes

·         Tectonic earthquakes are the most common type of earthquake.

              It may be of small or of extremely high magnitude.

·         Volcanic earthquakes occur usually after a volcanic activity has taken place. The magma that erupts during an earthquake leaves a space, to fill the space left by the magma the rocks move towards the space to fill it in, causing severe earthquake.

·          Collapse earthquakes are comparatively small earthquakes

     and they take place around underground mines.

·    The explosion earthquakes are caused due to the nuclear  explosions.

 EARTHQUAKE FORMATION

          Earthquakes develop in the crust of the earth. The crust    involves the earth's surface, submarine levels, down to the ocean floors. The inner part of the earth contains massive energy. Some of this energy escapes through cracks and other volcanic activity, but the bulk of it is stored within the earth’s inner part, contained in the crust.

After a period of time, the built up energy and movement causes huge tension in the plates, and there is massive pressure on the fault lines. This intense pressure resulting from energy build up causes the fault lines give way, and plates move over, against or apart from each other.

Stress in the earth’s outer layer cause a pushing effect against the sides of the fault.  Due to this motion, rocks slip or collide against each other releasing energy.  This released energy travels in waves through the earth’s crust and causes the shaking that we fell during an earthquake.

Under the surface of the earth, the two sides of a fault are constantly moving, relative to one another.  This movement is known as a fault slip.  The movement of these two sides is not smooth and is accompanied by a gradual build-up of elastic strain energy within the rocks along the fault.

The location on a fault where the slip first occurs is called the hypocenter, whereas the position directly above it on the ground surface is called the epicenter.

EARTHQUAKES MEASURES

      The strength of an earthquake can be measured by magnitude and          intensity.It is commonly measured on the Richter Scale which is an open-ended logarithmic scale.

Date	Location	Name	Magnitude
March 11, 2011	Pacific Ocean,  Tōhoku region, Japan	2011 Tōhoku earthquake	9.0[3][4][5]
February 27, 2010	Maule, Chile	2010 Chile earthquake	8.8
December 26,2004	Indian ocean,Sumatra	Indian ocean	9.1-9.3
January,12,2010	Aleppo, syria	Aleppo	Unknown
March 28, 2005	Sumatra, Indonesia	2005 Sumatra earthquake	8.6
September 12, 2007	Sumatra, Indonesia	2007 Sumatra earthquakes	8.5

EFFECTS OF EARTHQUAKES

Direct Effects:

1. Ground failures(or instabilities due to ground failures) surface faulting surface or fault rupture, or effects of seismic waves,

Ground cracking, Liquefaction.

2.  Vibrations transmitted from the ground to the structure

Indirect Effects: 

1 .  Tsunamis

2 .    Landslides

3 .    Floods

4 .     Fires

   Ground shaking

 The principal cause of earthquake-induced damage is ground shaking. As the earth vibrates, all buildings on the ground surface will respond to that vibration in varying degrees. the effect of ground shaking on buildings is a principal area of consideration in the design of earthquake resistant buildings.

Ground failure

 Earthquake-induced ground failure has been observed in the form of ground rupture along the fault zone, landslides, settlement and soil liquefaction. can occur in low density saturated sands of relatively uniform size. The phenomenon of liquefaction is particularly important for dams, bridges, underground pipelines, and buildings standing on such ground