WHY DO EARTHQUAKES OCCUR?
 
Earth layers

Earth can be said to be made up of four layers as under:

  • Inner Core - which is presumed solid; is about 2450 km in diameter and consists essentially of iron with about 10% being made up of a combination of elements such as nickel, sulphur etc.

  • Outer Core -which is ~ 2150 km thick and is presumed to be liquid because it does not transmit shear waves.

  • Mantle - which is said to be ~2900 km thick where the rock temperature is near its melting point making the mass viscous. This forms about 70% of earth’s volume as compared to the Cores (inner plus outer) forming 27%.

  • Crust is the brittle top most layer. It varies in thickness from 5 to 40 km and consists of materials like granites and basalts. This layer is better studied by earth scientists because it is accessible.