Intensity Scales

The level of violence of seismic shaking varies considerably over the affected area. This intensity is not capable of simple quantitative definition and, particularly before seismographs capable of accurate measurement of ground motion were developed, the shaking was estimated by reference to intensity scales that describe the effects in qualitative terms.

Subsequently, the divisions in these scales have been associated with accelerations of the local ground shaking.

Intensity depends, however, in a complicated way not only on ground accelerations but also on the periods and other features of seismic waves, the distance of the point from the source, and the local geological structure.

Furthermore, it is distinct from magnitude, which is a measure of earthquake size specified by a seismograph reading.