Monday, September 30, 2013

Disaster management - Earthquakes

An earthquake occurs when rocks break and slip along a fault in the earth. Earthquakes occur due to deformation of crust and upper mantle of the earth. Due to heating and cooling of the rock below these plates, movement of adjacently overlying plates and great stresses, deformation occurs. Tremendeous energy can build-up between neighbouring plates. If accumulated stress exceeds the strength of the rocks, the rocks break suddenly releasing the stored energy as an earthquake.
The earthquake releases energy in the form of waves that radiate from the epicenter in all directions. The 'p' wave or primary wave alternately compresses and expands material in the same direction it is travelling. This wave can move through solid rocks and fluids. These are the fastest waves. The 's' wave or secondary wave is slower and shake the ground up, down, back and forth perpendicular to the direction in which it is travelling. Surface waves follow both the 'P' and 'S' waves.
The magnitude of an earthquake is measured in richter scale. The richter scale is logarithmic.


Liquefaction of ground
Ground displacement

There is virtually no technique to control the occurrence of earthquake. However, certain preventive measures can be taken to minimise the damage.
Minimizing development activity (especially construction, mining, construction of dams and reservoirs) in areas known to be active seismic zones.
Continuously monitoring seismic activity using 'seismographs' and alerting people regarding any recorded disturbance in advance.

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