Hi Larry,

That's true for shallow, regional events within about 600 km.  For 
teleseismic events an
emperical table is used.

I've posted the table and Ray Buland's FORTRAN code, which is used by NEIC 
to compute mb.  See:
http://jclahr.com/science/software/mb/

Cheers,
John




At 07:39 PM 3/29/2005, you wrote:
>Stephen,
>
>WinQuake uses the following formula to calculate mb magnitude
>
>mb = log10(A/T) + 0.01*D + 5.9
>
>A = Peak P wave displacement amplitude in micrometers, T = Period of the 
>displacement amplitude and D = Distance in degrees
>
>See http://www.eas.purdue.edu/~braile/edumod/as1mag/as1mag3.pdf for more 
>information.
>
>Regards,
>Larry Cochrane
>Redwood City, PSN
>
>Stephen & Kathy wrote:
>>mornin,    I've been trying to find a table or chart or formula which 
>>will yield the Q(Delta,h), distance and depth values which I can use to 
>>plug into the Mb magnitude formula!!   Thanks in advance for any help in 
>>finding it!!!
>>    Stephen
>>    PSN Station #55
>>    near Pilot Hill Ca. USA
>>    38.828N  120.979W
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