GeologyRocksEarthquake Scales
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Earthquake Scales
Tue, 04/22/2008 - 22:03Intensity - amount of damage at one place
Americans use the Modified Mercalli Scale, this side of the pond we use the European Macroseismic Scale EMS 98
Richter Scale is (was) magnitude (i.e. the energy release of the 'quake)
Calibrated for California as there is a distance from epicentre term matched to Californian crust. Also only applied to the ancient Wood-Anderson (1925) seismograph
ML, local magnitude -matched to 'Richter' magnitude
MS, Surface wave magnitude
mb, Body wave magnitude
Mw, Moment magnitude (conversion from seismic moment - a more meaningful determination of earthquake power)
Note also that an increase of one unit on the 'Richter Scale' is almost 32 times IN ENERGY (it is 10 times AMPLITUDE recorded on seismograph) [2 units = 1000x energy]
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The logarithmic scale
Wed, 04/23/2008 - 13:46The logarithmic scale astounds me every time. Just because when you stop to think about it, a change from 2 to 4 on the scale is 100 times as powerful, 2 to 7 is 100,000!. That just really puts the range of power of these things in a little better perspective and makes me awe at what ol' mother nature can do.
I don't know if they do it over there in the UK, but here in the US the media often relates the power of the earthquake to nuclear bombs, usually the ones the US dropped on japan.. It's one thing I hate because I think it densensitizes us to the destruction of those cities in Japan, and I think it's insensitive to say "this earthquake had the power of 1,000 Hiroshima bombs." but nevertheless they do it, and it does put the power in a little greater perspective.
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well I guess I mistyped when
Thu, 04/24/2008 - 18:22well I guess I mistyped when I used powerful, as that is in terms of energy. I was going strictly from the log scale, where for example 1 is x10, 2 is x100, 3 is x1000. Just doing the multiples of 10 for size of the quake. Though basing the difference on energy would make for an even more astounding relativity.
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Amplitude vs Energy
Thu, 04/24/2008 - 23:03It is an important distinction between amplitude and energy (which is proportional to the square of amplitude).
Both are technically 'logarithmic'
Amplitude of the wave goes as you describe
log10-1(magnitude difference) = amplitude difference
For energy ...
log10-1(magnitude difference*1.5) = energy difference
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Earthquake Scales
Submitted by al8301 on Tue, 04/22/2008 - 09:34.The 'earthquake stats' topic made me realise how little I understand of ways of defining earthquake 'strength'. I'll put down what I (think I) know below and would appreciate additions and corrections.
Mercalli Scale: Defines 'damage caused'. Based entirely on surface damage so dependent on building quality, building density and surface geology as well as earthquake 'strength'
Richter Scale: Defines 'intensity'. Log scale, was taught it was only applicable to Southern Californian earthquakes but not sure why?
Magnitude (ML): Also defines 'intensity. Log scale, worldwide standard to do same thing as Richter scale
What other scales are there? What glaring errors have I made above?