GEOL 4714

This tutorial walks you through an example of using the Seismic refraction modeling software that comes with the Burger textbook.

This discussion presumes familiarity with Macintosh computer operations and background in refraction seismics. Examples are discussed in Burger's Appendix A. You should have available a MAC Disc with Burger’s Chapter 3 software, or be working on one of the Benson computers that has the Burger software pre-loaded. I also have a few copies of the Burger software on ZIP disks if you wish to work on a Macintosh computer that only has a ZIP drive. This software only runs on macs — don’t try it on a PC.

Insert the disc (an icon labeled "Burger.Ch2_3_4" or something similar appears) (this step is not necessary on the Benson 3^rd floor macs). Double click on the icon. A window opens showing icons for Chapters 2, 3 and 4. Double click on "Chapter 3". A window labeled "Chapter 3" opens showing many icons. Double click on "RefractModel". A title window labeled "Refract Model" appears, single click on it. A new menu appears at the top of the screen. You are now in the program "RefractModel".

The details for operation of "RefractModel" are given in Burger's Appendix A. The following summary is an example you can duplicate as an exercise. Underlined words mean you click on that word. Bold means you type it in.

1. File New A menu labeled "Main Data" appears.(see Burgers Fig A-1) Follow the menu instructions and enter data into the menus shown in Fig A-2. As our test case we generate a 3-layer dipping model. Parameters to be entered are as follows:

2. File Plot Graph. This generates an X-T plot and a table of X-T data. To see one or the other click on Windows and make a choice.

(Anytime you make changes in the basic model, clicking on 'Plot Graph' starts the calculations as well as displaying the new X-T plot and the data that generated it)

3. File Print Print This will generate prints of both the Table of Travel Times (x-T) and the X-T plot (Figs 1 and 2 were generated that way).

There are other options you may wish to explore: Units, Edit ......But remember: you need to use File PlotGraph each time you make a change.

4. File Save your_initials.refraction.params Saves a file with the model parameters you entered in Step 1 under the name "your_initials.refraction.params" (or any name you type in).

You may now wish to save the x-t data (Fig. 2) and go to another program "RefractSolve" to interpret the X-T plot.

If, at a later time, you wish to rerun this model,open RefractModel

File Open (move highlight to "your_initials.refraction.params") Open and proceed as before.

5. Transfer, RefractSolve, Yes your_initials.refraction.xt Save, Yes, RefractSolve

At this point you have saved the X-T data in the file "your_initials.refraction.xt" and should be in the "RefractSolve" program .

6. File, Open, (move 'highlight' to your_initials.refraction.xt ) Open

The X-T plot should be on the screen (Fig. 1). The next task is to draw lines connecting equal velocity arrivals.

7. Direction Forward. The cursor is now in the form of a + and you will use it to draw lines on the X-T values from left to right (forward direction). Click and hold while you move the cursor to the end of the first segment. Release. Put the cursor on the beginning of the second segment ,click and hold while you move the cursor to the end of the second segment. Release. Repeat for the third segment.

8. Direction Reverse. Repeat step 7 for the reverse direction. Fig. 3 shows the interpretation I did.

9. File Draw Structure. You now should have a sketch of the geologic picture (Fig 4) and a Table of the interpreted values (Fig. 5).

10. File Print Print Generates Figures 3, 4 and 5.

The programs described above can be used to interpret real data. Instead of beginning with a model, you can enter (X-T) data that you have "picked" from field seismograms. You begin by opening RefractSolve.

(In the following example I have used the data from Figure 2, except that in the the interest of speed I modified it to be for 12 geophones and only a "Forward" profile.

1A. File New

2A. Reverse Plot No

Main Data

Shot Offset	5
Spacing	10
Nos of Phones	12

Geophone Data

#1	10	>>>
#2	30	>>>
#3	50	>>>
#4	70	>>>
#5	80.4	>>>
#6	85.8	>>>
#7	91.1	>>>
#8	96.4	>>>
#9	98.5	>>>
#10	100.1	>>>
#11	101.7	>>>
#12	103.2	Done

2B. Direction Forward. The cursor is now in the form of a + and you will use it to draw lines on the X-T values from left to right (forward direction). Click and hold while you move the cursor to the end of the first segment. Release. Put the cursor on the beginning of the second segment ,click and hold while you move the cursor to the end of the second segment. Release. Repeat for the third segment.

3A. File Draw Structure (Figures 6, 7 and 8 appear)

4A. File Print Print (Figures 6, 7 and 8 are printed)

5A. File Save As your_initials.refraction.input (file is saved for possible later work)

6A. File Quit