## PSN-L Email List Message

Subject: Re: Mb question
From: Stephen & Kathy skmort@..........
Date: Tue, 29 Mar 2005 21:12:37 -0800

```Thanks Larry,,,    I did look at your help files on how winquake
calculates Mb,,  but it refers to a formula which requires the table,,
so I assumed you had a file with the table, but couldn't find it,,,
then I said, well I'll just let your program calculate Mb,,  but for
some reason it is not obvious to me how to do it????   That is when I
went looking for a table to set up my own calculation!!

Looking at Johns fortran info and table I realize it isn't as simple as
I first thought it would be,,,   a straight forward array, with depth on
one side and distance on the other would be something on the order of
800 by 108!!   The fortran table is 17 by 108!   And as near as I can
tell from the formulas, it isn't just bands of depth,,,   it appears
that the full range of Q is wider than the limits in the table???  Per
chance and just for fun, has anyone converted it to a PC or dos
program?????   Or perhaps a mathcad program???

Thanks all,,,  it is becoming a real education!!!

Stephen
38.828N  120.979W

Larry Cochrane 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
>
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