[irised] Frequency vs. Magnitude

[Michael Hubenthal]

Hi Katie,

I haven't seen a reply to your post yet so I will take a crack at a  
response.

In short, my guess is that the previous machine took some artistic  
liberties and it sounds like they weren't discussed in the manuals.   
There is a relationship between Period (1/frequency) and Magnitude  
however there are other factors involved.  For example the equation  
to determine magnitude using body waves is Mb = log(A/T) + s.  Where  
(A) is the amplitude of the P-wave train, the first arriving body  
wave, (T) is the period of the displacement, and (s) is a correction  
term.  Larry Braile suggest that for the AS-1 program s=0.01*D + 5.9  
where D is distance to the event.

The problem with describing the changes in shaking only in terms of  
magnitude only is that it doesn't account for other factors such as  
the distance to the epicenter, regional geology etc.  However, the  
folks at Pitsco probably just said, lets assume that all of these  
other factors are held as constants and put a magnitude sticker on  
there (or they may not have even thought about it that much).

I guess in thinking about your activity, what is the content that you  
want to convey to them?

Best Wishes
Michael








On Jan 22, 2008, at 12:15 PM, Katie Stofer wrote:

> >From the Maryland Science Center ...
>
> I have a more general question about quakes that I hope one of the  
> experts can help me with. We have been using a machine to simulate  
> earthquakes that ostensibly varies magnitude - Pitsco's Epicenter  
> Earthquake Simulator. They no longer make this and now sell instead  
> the EQ Tremor Table, which, instead of magnitude, varies cycles per  
> second (frequency), from 0-30, "in the range of P waves." So, is  
> there a relationship between frequency and magnitude (the latter  
> being the one that school groups visiting the science center are  
> more familiar with)? Was our original machine really varying  
> magnitude (being built, as far as I can tell, on some sort of belt  
> sander with a variable voltage control), or just frequency as far  
> as anyone can tell?
>
> Any ideas/insight are appreciated before I rewrite our entire  
> program due to a broken simulator!
>
> Thanks,
> Katie Stofer
> -- -- Kathryn Stofer TerraLink Exhibit Manager Maryland Science  
> Center 601 Light Street Baltimore, Maryland 21230 410/545-5976  
> 410/545-5974 fax BODYWORLDS - Coming to MSC Feb. 2 - Sept. 1, 2008!
> _______________________________________________
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> irised at iris.washington.edu
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---------------------------------
Michael Hubenthal
Education Specialist
IRIS Consortium
607-777-4612
www.IRIS.edu
hubenth at iris.edu