## PSN-L Email List Message

**
Subject: Re: Mb question: correction**

From: John or Jan Lahr JohnJan@........

Date: Tue, 29 Mar 2005 20:37:00 -0700

Hi Larry,
I spoke too soon!!! You were correct. The formula you gave is an
alternative to the more complex one for mb using a table.
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/
Looking at: http://www.eas.purdue.edu/~braile/edumod/as1mag/as1mag3.pdf
I see that, given:
A is amplitude in microns
D is distance in degrees
T is period in seconds
Larry Braile gives this formula for MS:
MS = log10(A/T) + 1.66*log10(D) + 3.3
and this formula for mb:
mb = log10(A/T) + 0.01*D + 5.9
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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