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The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or strength of an earthquake – an event occurring at greater or lesser depth. (The "M w" scale is ...
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.
The first scale for measuring earthquake magnitudes, developed in 1935 by Charles F. Richter and popularly known as the "Richter" scale, is actually the Local magnitude scale, label ML or M L. [11] Richter established two features now common to all magnitude scales.
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The 1965 Valparaíso earthquake (also known as the La Ligua earthquake) struck near La Ligua in Valparaíso Region, Chile, about 140 km (87 mi) from the capital Santiago on Sunday, March 28 at 12:33 local time. The moment magnitude (M w ) 7.4–7.6 earthquake killed 400–500 people and inflicted US$1 billion (adjusted for inflation) in damage.
Isoseismal map for the 1968 Illinois earthquake. In seismology, an isoseismal map is used to show countour lines of equally 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.
An earthquake struck Turkey's eastern Erzincan Province at 1:57:23 a.m. on 27 December 1939 local time with a moment magnitude of 7.8 M w and a maximum Mercalli intensity of XII (Extreme). It is the joint second most-powerful earthquake recorded in Turkey, tied with the 2023 Turkey–Syria earthquakes .
For example, the United States Geological Survey does not use this scale for earthquakes with a magnitude of less than 3.5, [citation needed] which includes the great majority of quakes. Popular press reports most often deal with significant earthquakes larger than M~ 4.