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[Phys-L] Re: earthquakes +- critical thinking



Seems to me that the elastic strain energy will scale with the square
of the elastic strain, yes? So small earthquakes that reduce the
strain could have a significant effect on lowering the total
available strain energy.

Comments always welcome,

joe


Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556

On Jan 2, 2006, at 11:57 AM, David Bowman wrote:

Regarding John Denker's complaint about the TDC program on tsunamis:

The Discovery Channel has been running programs about tsunamis.

Near the end of one program, they interviewed some big-shot
professor who wanted to reduce the risk by triggering small
earthquakes. He stood on the beach and said into the camera that
you would need 10 or maybe 100 magnitude-3 earthquakes to take the
place of onemagnitude-8 earthquake.

I muttered something like "what an idiotic thing to say." One of my
relatives, who had been watching the program, said she didn't
believe him; specifically, she didn't think he had any way of
actually triggering the earthquakes. I said that's not a strong
argument; that's just your opinion against his; you can't *prove*
there is no possible triggering mechanism.

My point is that there's a much stronger argument -- an irrefutable
*physics* argument -- that *proves* the proposed scheme cannot
possibly work.

This makes an amusing exercise ... definitely not a plug-and-chug
exercise ... definitely not an ACT "science reasoning" question
(i.e. 40 questions in 35 minutes). So, what's the proof?

====

As I recall, a change of one unit by one earthquake magnitude point
corresponds to a factor of 10^1.5 in released elastic strain energy.
This means that a magnitude 8 quake releases about 10^7.5 times as
much elastic strain energy as a magnitude 3 quake. I thus have a
hard time seeing how only 10^2 - 10^3 magnitude 3 quakes could have
much effect in defusing a potential magnitude 8 quake by dissipating
the built up strain energy involved.

David Bowman
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