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v. t. e. 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 " Mw ...
In 1902, Italian seismologist Giuseppe Mercalli, created the Mercalli Scale, a new 12-grade scale. Significant improvements were achieved, mainly by Charles Francis Richter during the 1950s, when (1) a correlation was found between seismic intensity and the Peak ground acceleration (PGA; see the equation that Richter found for California).
AD 62 Pompeii earthquake. On 5 February AD 62, an earthquake of an estimated magnitude of between 5 and 6 and a maximum intensity of IX or X on the Mercalli scale struck the towns of Pompeii and Herculaneum, severely damaging them. The earthquake may have been a precursor to the eruption of Mount Vesuvius in AD 79, which destroyed the same two ...
Richter established two features now common to all magnitude scales. First, the scale is logarithmic, so that each unit represents a ten-fold increase in the amplitude of the seismic waves. [ 12 ] As the energy of a wave is proportional to A 1.5 , where A denotes the amplitude, each unit of magnitude represents a 10 1.5 ≈32-fold increase in ...
The Mercalli intensity scale uses personal reports and observations to measure earthquake intensity but PGA is measured by instruments, such as accelerographs. It can be correlated to macroseismic intensities on the Mercalli scale [ 3 ] but these correlations are associated with large uncertainty.
The earthquake was 6.5 on the M w scale, with a maximum perceived intensity of IX (Violent) on the Mercalli intensity scale. However, most of the intensity measurements were consistent with an overall maximum intensity of VII ( Very strong ), and only the damage to a single structure, the Imperial County Services building in El Centro , was ...
e. An interplate earthquake is an earthquake that occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. [1] If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to ...
The 1857 Fort Tejon earthquake occurred at about 8:20 a.m. (Pacific time) on January 9 in central and Southern California.One of the largest recorded earthquakes in the United States, [6] with an estimated moment magnitude of 7.9, it ruptured the southern part of the San Andreas Fault for a length of about 225 miles (350 km), between Parkfield and Wrightwood.