Seismic intensity scales

Intensity scales are based on the observed effects of the shaking, such as the degree to which people or animals were alarmed, and the extent and severity of damage to different kinds of structures or natural features.

The intensity of shaking depends on several factors: Site response is especially important as certain conditions, such as unconsolidated sediments in a basin, can amplify ground motions as much as ten times.

Where an earthquake is not recorded on seismographs an isoseismal map showing the intensities felt at different areas can be used to estimate the location and magnitude of the quake.

For instance, thick layers of soft soil (such as fill) can amplify seismic waves, often at a considerable distance from the source.

[6] The first recognizable intensity scale in the modern sense of the word was drawn up by the German mathematician Peter Caspar Nikolaus Egen in 1828.