00:00 [music]
00:06 An earthquake magnitude measures the energy released by the rupture of the fault causing the quake.
00:12 The magnitude is calculated from the amplitude and duration of ground motion, recorded by seismological instruments.
00:19 Magnitude is a logarithmic quantity.
00:22 A one degree increase on the magnitude scale corresponds to a release of energy 30 times greater.
00:29 The Richter scale is one of many units of magnitude, but seismologists prefer to use the moment magnitude scale.
00:36 There is a relationship between the magnitude of the quake, the size of the fault, and the shift between the two blocks separated by the fault.
00:43 Seismic intensity, by contrast, measures surface damage.
00:48 It characterizes the severity of ground shaking in a given location by considering the effects of the shaking on people and man-made structures.
00:55 The depth of the quake, as well as the type of rocks crossed by the seismic waves, influence the intensity.
01:01 For the same quake, the intensity can vary from one place to another.
01:05 Two quakes of the same magnitude can have different maximum intensities and vice versa.
01:10 Intensity depends on the distance from the seismic focus and decreases away from it.
01:15 The scales range from 1 in regions where the shake is imperceptible to 12 where ground structures are destroyed.
01:23 [sound effects]
01:26 [silence]
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