Vocabulaire FormaTerre: variable: Macroseismic intensity

Macroseismic intensity

A cumulative measure of the effects of an earthquake at a particular place at the Earth’s surface on humans and (or) structures and thus a measure of the strength of earthquake shaking. Different from magnitude, the intensity at a point depends not only on the earthquake strength (released seismic energy) or earthquake size (released seismic moment), but also on the epicentral distance, the focal depth, the position of the observation point with respect to the type of focal mechanism and its directivity, and the local site conditions. Intensity values are usually given as integer Roman numerals ranging from 0 to 12 (see intensity scales, macroseismic). Although coarse, they are a valuable complementary analogue for physical ground motion parameters, correlating best with ground velocity. Moreover, intensity of shaking, based on the assessment of real post-event damage, is a suitable site-related empirical risk estimator for scenario calibrations. See Chapter 12 of this Manual. Intensity is now also quantitatively estimated using ground motion measurements; such quantitative intensity measurement is called “Instrumental Intensity” to distinguish it from the qualitative seismic intensity.

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