You will use a demonstration version of the program RESIX, which is available from Interpex of Golden, CO. The demonstration program is free, but you can not save or print the results.

(Since Resix runs only on DOS, Windows95, and Windows98, you may have to use the alternative VES 1.3 program. See the instructor to adapt this exercise to VES.)

To download your own copy of the program and its support files, follow the link below in your web browser.

	http://www.seismo.unr.edu/ftp/pub/louie/class/hydro/resix/

  demo.rxp      127 Kb    Mon Oct 23 00:00:00 1995 
  readme.1st      1 Kb    Mon Oct 23 00:00:00 1995 
  resix.exe     254 Kb    Mon Oct 23 00:00:00 1995 Binary Executable
  resix.gif       5 Kb    Mon Nov  6 00:00:00 1995 GIF Image
  resixd.ovl    295 Kb    Mon Oct 23 00:00:00 1995 

• RESIX2DI
• RESIXP
• TEMIXXL

Run the RESIX program in Windows by opening the folder where you downloaded into above, and then double-clicking on the resix DOS window icon. A DOS window will appear and start RESIX.

1. On a PC run ``resix''
2. enter ``C'', then enter, and you will get to a menu screen
3. use the right arrow key to move to "calculate"
4. use the down arrow key to move to "interpret"
5. hit enter, then ``8'' for Windows's VGA display, then ``8'' for the normal 640x480 window, then hit enter (no need to force BIOS graphics)

Press a key; then you will see the log-log plot of purple data points with a menu of key commands in yellow below. Press ``F'' for a forward calculation and you will see a yellow line near the bottom, at a default low resistivity. Answering the questions above should tell you why the apparent resistivities computed from this one layer appear as a series of line segments. Pressing ``M'' and then ``E'' to edit the model as a dashed green line directly on the plot with the mouse is fairly effective. You can press ``I'' to force an inversion to match your layers to the data better, once you have the right number of layers at about the right depths.

• Task 1) Modify the model to get the best fit of the data. Start by adding a layer to match the first part of the curve, then add another layer to match the second part of the curve. When you get the major parts of the curve right use the inverse function to find the best match. Write down the layer thickness and resistivities for the model that has the least error. (For this example the error should be less than 8%.) Make sure you report the:
  • Layer numbers?
  • Layer depths (to bottom of each layer)?
  • Layer resistivities?
  • Error of model (one value for the model)?

• Task 2a) To determine how well defined the thickness of layer 2 is, increase the depth of the bottom of layer 2 until the error is 1.05 times the error of your best fit model from task 1. Report:
  • Maximum depth of layer 2?

• Task 2b) Decrease the depth of layer 2 until the error is 1.05 times the error of your best model from task 1. Report:
  • Minimum depth of layer 2?
  Try adjusting layer 2's resistivity to get the error back to what it was before you changed the depth. Explain how layer 2's resistivity changed as layer 1 changed from maximum to minimum thickness. Using the charts handed out at the lectures on electrical properties of saturated rocks, speculate on the possible range of porosity in layer 2, and alternatively on the possible range of its water quality.

• Task 3a) To determine how well defined the resistivity of layer 1 is, increase the resistivity of layer 1 until the error is 1.05 times the error of your best fit model from task 1. Report:
  • Maximum resistivity of layer 1?

• Task 3b) Decrease the resistivity of layer 1 until the error is 1.05 times the error of your best model from task 1. Report:
  • Minimum resistivity of layer 1?
  Propose changes in the field procedures used to gather these data that would allow a better determination of layer 1's resistivity. Consult the characteristic curves handed out during lecture. Are there other EM (not galvanic) surveying techniques that could be helpful?