How does the Mercalli scale and the Richter scale measure the strength of an earthquake?

Question

How does the Mercalli scale and the Richter scale measure the strength of an earthquake? What are the advantages and disadvantages of using each scale? Under what conditions would one scale be more beneficial to use than the other?

Answer 1

The Richter Scale is logarithmic. That means a 2.0 on the scale is ten times more powerful than a 1.0 on the scale and a 3.0 would be a hundred times more powerful. The main problem with the scale is the dispersion of the shock waves as it travels to the recording sites (multiple sites are needed to pinpoint the epicenter) the material the shock wave passes through may impede or intensify the vibrations.

None of my geology text books say much about the Mercalli Scale, but they are 15 years old. It is used to measure the damage on the surface. This can be misleading because the damage can relatively minor on the surface but quite extensive 100 m down.

Answer 2

This is long... sorry
EQ = earthquake
MS = Mercalli Scale
RS = richter scale
Mercalli scale measure the intensity and is more descriptive than the Richter Scale that measures the magnitude. The modified Mercalli Scale ranges from I to XII with XII being the most severe. The Mercalli Scale provides a measure of environmental damage usually measured from VI and above
e.g. Intensity Description
1 not felt
4 windows rattle. Crockery disturbed
8 sand and mud ejected
12 total damage. waves seen on ground surface
The Richter Scale measures the magnitude of the earthquake. Magnitude is logarithmemic. Measures how strong waves are.
Advantages of RS - tells us the extact magnitude of EQ
Advantage of MS - tells us environmental effect
Diadvantages of RS- does not tell us effect on environment
Disadvantages of MS- different magnitudes of EQ have different environemntal effects e.g. Newcastle RQ 1989 was (i think - cant find it in book) 5.6 on the RS but there was a lot of environmental damage. Therefore the MS is not a accurate as the Richter scale
if information on environemtnal damage is needed then you use the MS. However, if you want the magnitude of the earthquake to compare it to other EQ, you use the RS
i hope that helps you

Answer 3

Richter scale gives you the energy released at the point of focus. You can measure it any where from the point of epicenter. We need the instrument called seismograph to measure the force released during earthquakes. It is related with Richter scale. The maximum amount of shaking and the difference of arrival time of Primary waves to secondary waves are used for calculation.The result should be practically same. Each one represents ten fold in shaking and 32 times higher force is released for each scale. It is the combined measurement of distance and amplitude of shaking. There is no upper limit for it. But so for we have sensed only up to 9.5 in Richter scale. The Mercalli scale is more meaning full scale. Unfortunately not familiar for common people. It starts from 1 to 12.This scale is decided by the effect sensed by the people and news reports. For a same earthquake it will differ from place to place. It gives you the idea of intensity and damages. There is no meaning in comparing these 2 scales for its unit. One is not at all related with other. Please visit my slide show to know more on this.
My Community in Orkut
http://www.orkut.com/Community.aspx?cmm=26068261
Presentation slides
http://asia.pg.photos.yahoo.com/ph/quake

Answer 4

I wouldn't swear to this but from what I can remember of geology class they measure the force of an earthquake based on the vibrations or waves of movement that it produces. So they assign a rating based on how extensive the tremors are and at white type of frequency they are vibrating. Sorry that this is kind of vague but I don't remember it all exactly. Hope that is at least a little helpful.