Depending upon the possible causes, the earthquakes may be classified as:
1. Natural earthquake
2. Earthquakes due to induced activities.
Natural Earthquakes
Natural earthquakes may be due to
(i) active faults (ii) movement of tectonic plates or
(iii) due to volcanic eruptions.
In earths crust there are some faults which are not yet settled. The displacement of rocks along faults cause earthquake.
Tectonic means large scale process affecting the structure of the earthcrust. This process causes gradual movement of material within the crust of earth. Sometimes it shakes the earth crust.
Volcano is a mountain or hill having a crater through which lava, rock fragments, hot vapour and gas are or have been erupted from the earths crust. Occasionally the volcanoes become active and create earthquake near the mountain crater.
Earthquakes due to Induced Activities
These are caused by vibrations induced by atomic explosions and collapse of ground due to faulty mining.