Earthquake Terminology

( Seismology )

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.

Seismic zonation map of a country is a guide to the seismic status of a region and its susceptibility to earthquakes. India has been divided into five zones with respect to severity of earthquakes. Of these, Zone V is seismically the most active where earthquakes of magnitude 8 or more could occur.

When the earth is shaken to her (utmost) convulsion, And the earth throws up her burdens (from within), And man cries (distressed): 'What is the matter with her?'- On that Day will she declare her tidings: For that thy Lord will have given her inspiration. On that Day will men proceed in companies sorted out, to be shown the deeds that they (had done). Then shall anyone who has done an atom's weight of good, see it! And anyone who has done an atom's weight of evil, shall see it. (Holy Quran - 99)