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README   for migration velocity analysis         3 Sept 1996

This package contains Demos for migration velocity analysis by
perturbation.  The package consists of five directories.

1. This step is to generate synthetic data for the demo. For field data
   the user would skip this step and proceed with step 2.
Synvxz 	   to generate common offset synthetic data gathers;
Xmod       view the synthetic data (X-windows output)
PSmod      view the synthetic data (PostScript output)

2. Use a velocity model guess to migrate the input seismic data.
Unif2      to compute the v(x,z) velocity profile, and
           velocity derivative dVdv(x,z)

3.
Rayt2d 	   to generate tables of traveltime, traveltime derivatives
	   and cosin of emergence angle
Sukdmig2d  to migrate the synthetic seismograms to produce two outputs
           of prestack migrated data. One is with the primary amplitude
           and the other one with an extra amplitude that is a product
           of the primary amplitude and the depth derivative.
Xmig	   Show the results of migrations. Leave this plot on your
           screen while performing the next steps. 

4. Perform a velocity estimation based on residual moveout by Zhenyue Liu's
   perturbation method.

Surelan	  compute residual-moveout semblance for cdp gathers

The value to be picked is represented by the small high located near the
coordinates (390, -0.1)  in the (depth,r-parameter) space represented
by the semblance plot. Pick this value by placing the mouse cursor
on the center of the peak  and type:  sq   to save the value.

The shell script will prompt you to make additional, similar picks,
for each common shot inversion panel.

Run the next two shell scripts to generate the necessary velocity
perturbation value called: dlambda

Dzdv	  determine depth derivative with respect to velocity 
Velpert   estimate velocity parameter perturbation 

For the demo, this value of dlambda should be approximately 380.

Add the value of dlambda to the velocity used in Unif2
repeat steps 2, 3, and 4. This has been done for you via Unif2.1

To proceed with the next step of the demo, run:

Unif2.1		
Rayt2d
Sukdmig2d
Xmig

As before and then run

Reference: 
Liu, Z. 1995, "Migration Velocity Analysis", Ph.D. Thesis, Colorado
    School of Mines, CWP report #168.

John Stockwell	 | [e-mail]
Center for Wave Phenomena (The Home of Seismic Unix)
Colorado School of Mines
Golden, CO 80401 | http://cwp.Mines.EDU:3852/
voice: [phone]  |    fax: [phone].