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Moment magnitude is measured on a logarithmic scale.

What that means is that a movement of +1 on the scale (say from 5.5 to 6.5) indicates that the earthquake is ten times larger.

So, to work out how many times bigger one earthquake is than another (say 1940 and 1986), you get yourself a scientific calculator (online version here) and calculate the difference between the numbers:

7.7-7.1 = 0.6

(OK, you didn't need a calculator for that bit)

and then press "INV" followed by "log".  This converts the answer back into "regular" numbers, and in this case, gives an answer of 3.98.  So the 1940 quake was about four times more powerful than the 1986 one.

For discussion, I'll just throw in the thought that whether or not an earthquake is a catastrophe is measured by loss of life (and property). Is it possible that the buildings that replaced those destroyed in the 1940 quake were built to a higher standard, leading to a lower rate of collapse next time?

by Sassafras on Mon Jan 26th, 2009 at 02:51:25 PM EST
[ Parent ]
Actually, motion is one thing, power another: the multiplier for power is 30, not 10. So the 1940 quake was almost eight times more powerful than the 1986 one.

However, while I thought of the same as you, after some reading, the situation with the 1977 quake seems different, see my own reply to pereulok.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Mon Jan 26th, 2009 at 06:33:17 PM EST
[ Parent ]
I´ll try to forget the killed for a minute. Yeah, meybe yoy´re right, standards are lowered. However, sometimes what happens also is that there´s an urgent need of housing to be solved, so many cheap buildings "prefabricados" (I think the word is pre-assembling estructures, but I´m not sure) are built. They are said to be temporal (3-5 years), but in practise they stay. I don´t know if that´s the case in Romania, I just remembered the case of the Soviet "Jrushovkas", 5-storey buildings built during the Khruschov years that never were rebuilt, and becoming a real danger in Russian cities of provinces. But in Romania I´ve heard complanis that standards were lowered after 1940 and after 1977, but not fully complied with until 1989...

Another issue in Bucharest is the consequences for the urban development in the city. Buildings that were built didn´t respect style, height or anything... In a context of disrespect (people blame Ceacescu, but Ceaucescu just made huge -because he was a megalomaniac- the kind of unrespectful development of Bucharest historical centre that was the habit in the 70s and is still the habit nowadays. If you look at the hedquarters of the Union of Arquitect you would imagine what they are doing around here... As this is not the only but one of many cocrete+glass let´s see if we change from being called little Paris to being called little Berlin buildings in city centre.

http://www.flickr.com/photos/pereulok/2281943859/in/set-72157612909967720/

And an example of the kind fo buildings that were bbuilt were the 1940s/1977s collapsed:

http://www.flickr.com/photos/pereulok/2251542375/

"If you don't want a man unhappy politically, don't give him two sides to a question to worry him; give him one. Better yet, give him none." (Fahrenheit 451)

by pereulok on Tue Jan 27th, 2009 at 04:10:25 AM EST
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