Quote:
Originally Posted by Pawnmower
yah it was fairly minor , compared to 89
the Richter scale is crazy , If i understand it properly (every full mag = 10 times more power)
the earthquake we had was a 6.0 Mag
in 89 it was 6.9
so the 89 quake was 9 times more powerful than 2014........that seems almost impossible
But yah
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You're correct that a unit change on the magnitude scales used to measure earthquakes represents a 10-fold increase in what is being measured. That's because the magnitude scales are logarithmic and use 10 as a base. I heard a CNN science reporter incorrectly claim this morning that a 0.9 difference would be 9 times higher. That's a reasonable quick-and-dirty approximation, but the more exact description is that would instead be 10^0.9 (or 10 to the power to 0.9) higher, which is about 7.9 times stronger.
Further complicating matters, the magnitude scales describe amplitudes on a seismograph, not the actual energy. The amount of energy that is generated is more relevant in terms of what the earthquake can do. To convert relative differences in magnitudes into differences in energy, you have to multiply the difference in magnitude by 1.5 and then use that product as the exponent, as is explained by the USGS (
http://earthquake.usgs.gov/learn/top...uch_bigger.php)
In this case, the ratio of the energy from the two quakes (Loma Prieta versus Napa) would be
10 ^ (1.5 * 0.9) = 10 ^ 1.35 = 22.4
The above calculation is probably the basis for the USA Today article that reports that the 1989 Loma Prieta earthquake was "more than 22 times stronger" than the recent Napa earthquake.
http://www.usatoday.com/story/news/n...ison/14527315/
Pardon my being so pedantic about this. I'm a statistics professor and probably can't help it.
