Isoseismal map

In seismology, an isoseismal map is used to show lines of equal felt seismic intensity, generally measured on the Modified Mercalli scale. Such maps help to identify earthquake epicenters, particularly where no instrumental records exist, such as for historical earthquakes. They also contain important information on ground conditions at particular locations, the underlying geology, radiation pattern of the seismic waves and the response of different types of buildings. They form an important part of the macroseismic approach, i.e. that part of seismology dealing with non-instrumental data. The shape and size of the isoseismal regions can be used to help determine the magnitude, focal depth and focal mechanism of an earthquake.