Classification of Earthquakes

Factsheet

Based on magnitude, earthquakes may be classified as microearthquakes, slight-, moderate-, great- and very great as detailed below:

                                                                                      Magnitude

Microearthquake                                             -less than 3.0

Slight                                                               - 3.2-4.9

Moderate                                                         -5.0-6.9

Great                                                               -7.0-8.0

Very great                                                       - Greater than 8.0

Depending upon the epicentral distance of the earthquake, they may also be classified as local shock, near shock, distant shock and teleseismic shock as detailed below:

                                                                                    Epicentral Distance in degress

Local shock                                                     Less than 4.0

Near shock                                                      Between 4.0 and 10.0

Distant shock                                                  Between 10.0 and 20.0

Teleseismic shock                                            Greater than 20.0.

For the Earth as a whole, the frequency of occurrence of earthquakes in different magnitude is given below:

Magnitude (Ms)                                 Average number of earthquakes/year

            8.0                                                                   2

            7.0                                                                   20       

            6.0                                                                   100

            5.0                                                                   3,000              

            4.0                                                                   15,000

            3.0                                                                   >100,000

A list of damaging earthquakes in India during the last about ten years:

·         Uttarkashi earthquake of October 20,1991 (M:6.6).

·         Latur earthquake of September 30,1993 (M:6.3).

·         Jabalpur earthquake of may 22,1997 (M:6.0).

·         Chamoli earthquake of March 29,1999 (M:6.8).

·         Bhuj earthquake of January 26,2001 (M:6.9).