Isoseismal

Synonyms

Isoseismal line

Definition

An isoseismal (line) is a contour or line on a map connecting points of equal intensity relating to a specific earthquake and confining the area within which the intensity is the same.

Discussion

When an earthquake occurs, its intensity at a given site is determined through the classification of observed effects on humans, buildings, and on the natural environment. Today, these kinds of data are acquired from macroseismic surveys and, in some countries, also from standard questionnaires distributed to the public. The results are then compared to the effects classified in an intensity scale, in order to assign intensity values. All of the assigned values are subsequently placed onto a map; the zones with the same intensities are then bounded by the isoseismal lines and marked with a roman number (corresponding to the degree of intensity). The significance of isoseismals depends on the number of observations in each place and on the close distribution...