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Difference between magnitude and intensity

There are two parameters that are used to describe the size of earthquakes: magnitude and intensity.

Magnitude on the Richter Scale is a fixed value of measurement based on recordings of ground movement called seismograms. It correlates with the size of the hypocentre and the energy radiated in the form of seismic waves. A number of magnitude scales are in use which differ in terms of which seismogram information they use for calculation purposes. This is why different values of magnitude are often quoted for the same quake. The moment magnitude scale (Mw), which bears a direct relation to the dimensions of the quake's rupture surface, is becoming increasingly common. All scales of magnitude are logarithmic, the energy content of an earthquake increasing by a factor of 32 with each complete stage on the scale.

Intensity is an expression of the extent and distribution of damage caused by an earthquake. It is derived from a rough statistical analysis of local damaging effects on each type of building. The scale most commonly used worldwide is the Modified Mercalli Intensity Scale (MM) and its enhanced form, the European Macroseismic Scale (EMS-98). Another important – and again measurable – parameter is peak ground acceleration (PGA). This, together with its derivatives, velocity (PGV), and displacement (PGD), forms the basis for the earthquake-resistant design of buildings.

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