[Seisunix] Zero Offset VSP Processing

paulmichaels paulmichaels at boisestate.edu
Sun Aug 9 17:33:51 CEST 2020


It looks like you have a zero phase wavelet in your signals.  The place 
to pick first arrivals is the black maximum.  Your arrow is on a side 
lobe.  Zero phase wavelets can be the result of correlation, like with a 
Vibroseis source.  Also, they can be a wavelet of choice in some 
programs that compute synthetic data. If your data are synthetic, look 
into using a minimum phase wavelet, if it is available.


Dr. Paul Michaels, PE
Professor Emeritus, Engineering Geophysics

On 8/5/20 1:21 PM, Erdi Apatay wrote:
> Hello Everyone
> I said before that I was trying to do Zero Offset VSP Processing. To 
> do that, I tried to use free software is called MVSP and Crewes 
> toolbox. My problem is that I can start picking first break arrivals 
> from 4th trace, and I can not see and pick the first three traces when 
> I look at the data during the picking.
> The first software itself assigns negative values for the first three 
> traces, which results in negative velocities. On the Crewes, I am 
> trying to assign values like 0.001 0.002 0.003 before the 4th trace 
> because the 4th trace's time is 0.006, which probably gives rise to 
> wrong velocities.
> In short, Can I do anything about this issue on Seismic Unix? Is there 
> any chance to fix it?
> I added one of my files and the screenshot zoomed where the problem 
> is. I modeled and created this data on different code (fdelmodc). 
> **The data is passive data, and I utilized the noises, recording 120s. 
> So, when you look at my data, you need to zoom in to see closely.
> Thank you
> Best regards
> Erdi
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