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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 ...
That gave the Mercalli Scale, as well as the European MSK-64 scale that followed, a quantitative element representing the vulnerability of the building's type. [10] Since then, that scale has been called the Modified Mercalli intensity scale (MMS) and the evaluations of the seismic intensities are more reliable.
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 seismic energy (strength) of an earthquake. [13]
In other words, the earthquake zoning map of India divides India into 4 seismic zones (Zone 2, 3, 4 and 5) unlike its previous version, which consisted of five or six zones for the country. According to the present zoning map, Zone 5 expects the highest level of seismicity whereas Zone 2 is associated with the lowest level of seismicity.
The old Modified Mercalli intensity scale (MM), a relic of the pre-instrument days, remains useful in the sense that each intensity-level provides an observable difference in seismic damage. After many years of trying every possible manipulation of accelerometer-time histories, it turns out that the extremely simple peak ground velocity (PGV ...
However, this earlier scale did not include the subdivisions of intensity levels 5 and 6 into "upper" and "lower" categories, which had been introduced later in Japan. [52] In South Korea, a seismic intensity scale modeled after Japan’s was used in the past, but since 2001, the country has switched to the Modified Mercalli intensity scale. [53]
The magnitude/intensity comparison table in the Mercalli intensity scale#Modified Mercalli Intensity scale section makes it appear as though magnitude and intensity are directly comparable, when in reality, the magnitude (number) necessary for a certain intensity is frequently lower than the intensity (number) of the shaking it produces. An ...
Seismic Intensity Scale [1] [2] [3] Intensity Level (震度分級) Strong Ground Acceleration (cm/s 2,gal) Ground Speed (cm/s) What People Feel Effects Indoors Effects Outdoors; 0 Undetectable (無感) below 0.8 gal Imperceptible to humans 1 Slight (微震) 0.8-2.5 gal People may feel slight shaking when motionless 2 Weak (輕震) 2.5-8.0 gal