Earthquakes may be classified in several ways, according to the purpose in view. With regard to the manner of production, they may be grouped into volcanic and tectonic quakes, which will be explained when we take up the causes of these phenomena. For our present purpose, which is chiefly descriptive, it will be most convenient to divide earthquakes into: (1) Macroseismic, or large earthquakes which "disturb continental areas and frequently disturb the world as a whole" (Milne); and (2) Microseismic, or local earthquakes which, as a rule, affect areas of only a few miles' radius, rarely as much as 100 or 200 miles. While the macroseismic quakes are due to a disturbance both of the earth's crust and of the homogeneous interior, those of the microseismic class "appear to be the shiverings within the crust " (Milne).

It should be observed that these terms have been frequently employed in senses very different from those here used, which are taken from Professor Milne. That there should be no very distinct line of demarcation between the two classes, is not surprising, for they represent different degrees of intensity or violence in similar phenomena.