Earthquake Terminology

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Definitions:

Epicentre:

It is the point on the (free) surface of the earth vertically above the place of origin (hypocentre) of an eartquake. This point is expressed by its geographical latitude and longitude.

Hypocentre or Focus:

It is the point within the earth from where seismic waves orignate. Focal depth is the vertical distance between the hypocentre and epicentre.

Magnitude:

It is the quantity to measure the size of an earhquake in terms of its energy and is independent of the place of the observation.

Richter Scale:

Magnitude is measured on the basis of ground motion recorded by an instrument and applying standard correction for the epicentral distance from recording station. It is linearly related to the logarithm of amount of energy released by an earthquake and expressed in Richter Scale. 

Intensity:

It is the rating of the effects of an earthquake at a particular place based on the observations of the affected areas, using a descriptive scale like Modified Mercalli Scale.

Classification of earthquakes
Slight Magnitude upto 4.9 on the Richter Scale.
Moderate  Magnitude 5.0 to 6.9
Great Magnitude 7.0 to 7.9
Very Great
Magnitude 8.0 and more