Hi Geoffry,

To see the P arrival I normally just turn up the WinQuake Y scale.  Since 
the basic sensitivity is a better than 10nm/count, you can expand it quite 
a lot.

See: http://bnordgren.org/seismo/090803.175000.bhz-ph2.psn.gif

You can pretty well see where the Pn starts around 17:57:00 which is made 
clearer with a 0.2sec low-pass filter.  Looking at the arrival time tables, 
it would seem that you have the 5.8 with a predicted Pn arrival at 17:57:00 
getting its later phases mixed with the 6.9, which has a predicted Pn 
arrival at 18:01:33.  They are going to be pretty hard to untangle.

Regards,
Brett


At 08:02 AM 8/5/2009 -0700, you wrote:
>Hello Bob & Brett ;
>If you were looking only for first arrival times
>Id think High gain is the way to go.
>You must see the noise because the emerging
>signal can sometimes be a part of the noise.
>Many signals i get from this area seems
>to attenuate the P wave in a way it arises
>slowly out of the grass and in such a case
>where exactly is the first arrival time.
>Most not likely the time you actually see.
>If somehow you could use a FFT to see
>the first arrival time I think that may be
>the way to go but since you need many
>samples to use the fft it may not be possible
>to see the exact arrival.
>Does anyone know of processing routines
>that will pull a signal out of the grass other
>than a FFT routine ??


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