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Seismic intensity scales categorize the intensity or severity of ground shaking (quaking) at a given location, such as resulting from an earthquake.They are distinguished from seismic magnitude scales, which measure the magnitude or overall strength of an earthquake, which may, or perhaps may not, cause perceptible shaking.
Isoseismal map for the 1968 Illinois earthquake. The irregular distribution of shaking arises from variations of geology and ground conditions. The Earth's crust is stressed by tectonic forces. When this stress becomes great enough to rupture the crust, or to overcome the friction that prevents one block of crust from slipping past another ...
It is often used within earthquake engineering (including seismic building codes) and it is commonly plotted on seismic hazard maps. [6] In an earthquake, damage to buildings and infrastructure is related more closely to ground motion, of which PGA is a measure, rather than the magnitude of the earthquake itself.
A type of seismic zone is a Wadati–Benioff zone which corresponds with the down-going slab in a subduction zone. [2] The world's greatest seismic belt, known as the Circum-Pacific seismic belt, [3] is where a majority of the Earth's quakes occur. Approximately 81% of major earthquakes occur along this belt.
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The effects of any one earthquake can vary greatly from place to place, so many MMI values may be measured for the same earthquake. These values can be displayed best using a contoured map of equal intensity, known as an isoseismal map. However, each earthquake has only one magnitude.
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Earthquakes in the New Madrid and Wabash Valley seismic zones from 1974 to 2002, with magnitudes larger than 2.5. The zone had four of the largest earthquakes in recorded North American history, with moment magnitudes estimated to be as large as 7 or greater, all occurring within a 3-month period between December 1811 and February 1812. Many of ...