It will be seen that there is a certain rough correspondence between these curves and the isoseismal lines.
An isoseismal line is a curve which passes through all points at which the intensity of the shock was the same.
The only complete map of the isoseismal lines is that drawn by Professor Mercalli.
Within the isoseismal 3, buildings were more or less slightly damaged.
It will be noticed that large portions of them, and especially of the isoseismal 4, traverse the sea.
The curve for the first degree (A) coincides of course with the isoseismal line of intensity 2.
Outside the isoseismal 4, the earthquake was observed at several places.
In this case, the elongated forms of the isoseismal lines cannot be attributed to variations in the nature of the surface rocks.
That isoseismal along which the decline of energy is most rapid was called by K. von Seebach a pleistoseist.
Secondly, it will be noticed (Fig. 60) that the isoseismal lines are not equidistant from one another.