Dear Murray,

I received your message from Larry Cochrane about setting up a display
to illustrate the Richter magnitude scale.  One thing to keep in mind is
that, approximately,  for each unit increase magnitude the amplitude of ground
motion goes up by a factor of ten and the duration of shaking increases
by a factor of 3 so that the energy radiated increases by a factor of
10x3 = 30 (actually 10 raised to the 1.5 power, or 32).

Could you describe in more detail what you have in mind for the exhibit?
What will the seismic display look like?  Is it on paper or on a computer
screen?  What did you want the code to do, automatically computer a
magnitude?

It might be helpful to have a meter that indicates the average
amplitude of the signal.  The input would need to be filtered so that
the needle would not bounce with each peak and trough of the
ground motion.  Then you could mark the dial with one point
indicating "maintain this amplitude for 1 sec for a magnitude 1"
The next point with 10 times the amplitude would be labeled:
"maintain this amplitude for 3 seconds for a magnitude 2"
If the scale can register a signal 100 times greater than the
magnitude 1 signal, then this point would be labeled
"maintain this amplitude for 10 seconds for a magnitude 3."

Regards,
John





John C. Lahr
lahr@........  (work)
john@........  (home)

Central Region Geologic Hazards Team
U.S. Geological Survey
PO Box 25046
Denver, CO 80225
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