Isoseismal map

In seismology, an isoseismal map is used to show countour lines of equally felt seismic intensity, generally measured on the Modified Mercalli scale.

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.

In the case of recent earthquakes, news reports are augmented by sending out questionnaires or by collecting information online about the intensity of the shaking.

Because of local variations in the ground conditions, isoseismals generally separate zones of broadly similar felt intensity, while containing areas of both higher and lower degrees of shaking.

[8] In some earthquakes, more than one maximum exists because of the effect of ground conditions or complexities in the rupture propagation, and other information is, therefore, required to identify the area that contains the epicenter.