Depending upon their mode of origin, the earthquakes are classified into the following groups.
- Earthquake due to surface causes: Earthquakes may be generated by landslips and collapse of the roofs of underground caverns and other surface disturbances. Most of these are very minor, and some are even rarely felt. All causes of an earthquakes
- Earthquake due to volcanic causes: Volcanic eruptions may also produce earthquakes but such earthquakes are generally very feeble.
- Earthquake due to Tectonic causes: Tectonic earthquakes are the most common and numerously occurring earthquakes on the earth. They are powerful and very disastrous earthquakes, which possess a tremendous amount of energy to ruin the structures. They are caused by shocks, which originate in the earth’s crust due to the sudden slippage of the two transversely moving tectonic plates.
Earthquakes can also be classified on the basis of depth of focus. There are three types of earthquakes classified on the basis of depth of focus.
- Shallow focus earthquakes: Earthquakes having a depth of focus 55 km or less are known as shallow earthquakes.
- Intermediate focus earthquakes: Earthquakes having a depth of focus ranging from 55 km to 300 km.
- Deep focus earthquakes: Earthquakes, which have a depth of focus between 300 to 650 km.