I found this brainstorm at CBC News. In a report on the Japanese earthquake, CBC meteorologist Johanna Wagstaffe opined:
" A magnitude 8.9 quake is actually 8,000 times more powerful than a 7.2 quake," said Wagstaffe. " Because the earthquake occurred under the ocean floor, massive amounts of water were displaced above the shaking ocean ground, generating a tsunami."
8,000 times? We know the Richter scale works on factors of ten. An 8.0 magnitude quake, for example, would be ten times greater than a 7.0 tremblor. Hence a 9.0 quake would be one hundred times more powerful than a 7.0. What beggars belief is how Wagstaffe comes up with the math than an 8.9 quake is eight thousand times more powerful than a 7.2.
If anything, meteorologists know far less about seismology than climatology. They're trained to guess whether it's going to rain tomorrow, not whether you've got a tsunami in your future. Yet when a story like the Japanese quake arrives, everybody and their cousins get to weigh in, even if they really know squat.
It's been reported in Australian papers that Japan's 8.9 is 8,000 times the 6.3 Christchurch quake. I've not read anything about 8.9 to 7.2 comparisons.
ReplyDeleteI wish somebody could explain that to me. This seems a bit ambiguous. When it comes to damage there are factors beyond force including distance from epicenter, the depth of the quake, its duration, the surface topography and man-made elements.
ReplyDeleteFrom what I understand of Richter scale measurements, a 7 would be 10X a six. An 8 would be 10X10 or 100X a 6. A 9 would be 10X10X10 or 1,000X a 6. Something around a 9.8 would approximate 8,000X a 6.
But we can't place too much emphasis on the number value. Remember Christchurch was hit by a relatively harmless low-7 quake a month before the deadly mid-6 tremblor.
I can help (after a trip to Wikipedia. The Richter scale measures the shaking amplitude/magnitude.
ReplyDeleteThe energy release is actually a factor of 31.6 between each 1.0 magnitude difference. An 8.9 corresponds to ~7900 times the energy released by a 6.3 earthquake.
I have to assume that Wagstaffe mistakenly said 7.2 instead of probably 6.2...
Like you said, though, the energy released by a quake is as pointless as the category of a hurricane (such as Category 3 Katrina at landfall). There are plenty of other factors involved.
Johanna Wagstaffe is both a meteorologist and a seismologist! Bio: www.cbc.ca/vancouverweather/bio/
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