(Raymond Yeung) wrote in
om:

Snipola
Incidentally, I learnt that earthquake magnitue is more
of log scale - every increment causes a 30 fold increase in released
energy. A major one is something of 7 or above. Think about the last
one that's about 6, and then multiply that by 30, and with epicenter
right in the neighbourhood.
Snipola

To be exact, the scale is calibrated such that a difference of 2
in magnitude represents a 1000 time increase in energy released.
So a difference of 1 magnitude is sqrt(1000) or about 31.623.

So a 7 is about 32 times more powerful than a 6, and 1000 times
more powerful than a 5.

This is also why the idea of triggering smaller quakes to release
the stress wouldn't work. To release the stress of a magnitude 7
quake would require 1000 magnitude 5 quakes, or 1 million magnitude
3 quakes!!!!

I did the calculations once to figure out how often a triggered
quake would have to be done to release the stress of a large San
Andreas event. Turns out you'd have to have a mag 3 to 4 triggered
quake every few minutes. Not something most people would put up with.

Here's a nice web page giving the formulas relating magnitude to
energy released. There's also a chart comparing various magnitude
quakes tons of TNT.

http://staff.imsa.edu/science/geophy.../eqenergy.html

PS. as a curiosity, there is such a thing as a magnitude 0 quake!!!

Brian
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