The magnitude measures the energy released by the rupture of the fault causing an earthquake. Seismic intensity, in contrast, measures surface damage.
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00:00An earthquake magnitude measures the energy released by the rupture of the fault causing
00:11the quake.
00:12The magnitude is calculated from the amplitude and duration of ground motion, recorded by
00:17seismological instruments.
00:21Magnitude is a logarithmic quantity.
00:22A one degree increase on the magnitude scale corresponds to a release of energy 30 times
00:28greater.
00:29The Richter scale is one of many units of magnitude, but seismologists prefer to use
00:34the moment magnitude scale.
00:36There is a relationship between the magnitude of the quake, the size of the fault, and the
00:41shift between the two blocks separated by the fault.
00:44Seismic intensity, by contrast, measures surface damage.
00:48It characterizes the severity of ground shaking in a given location by considering the effects
00:53of the shaking on people and man-made structures.
00:56The depth of the quake, as well as the type of rocks crossed by the seismic waves, influence
01:01the intensity.
01:02With the same quake, the intensity can vary from one place to another.
01:05Two quakes with the same magnitude can have different maximum intensities, and vice versa.
01:11Intensity depends on the distance from the seismic focus and decreases away from it.
01:16The scales range from 1 in regions where the shake is imperceptible, to 12 where ground
01:22structures are destroyed.