Instructions

Here is a pseudosection of resistivity data gathered over two trenchs that were back-filled with construction grade gravel. One of the trenchs was not bracketed fully by this line of data. The host material is a more resistive soil, and the entire region is saturated with water.

1) Does the pseudosection indicate that there is soil on top of the trench, and how can you tell?
Yes
No

2) Does the pseudosection indicate that the bottom of the trench has been imaged, and how can you tell?
Yes
No

3) At what line position is the centre of this trench? To answer - click the correct location on image!

4) Find the voltage that was recorded for the n=3 data point gathered directly over the trench centre, assuming the corresponding apparent resistivity value is 77 Ohm-m and the input current was 1 Amp.

5) Is this apparent resistivity of 77 Ohm-m likely to be more than, or less than, or equal to, the true (intrinsic) resistivity of the gravel back-fill, and why?
more than
less than
equal to

6) Pseudosections do not have a depth scale; however, it is useful to have some idea of what you are dealing with before applying inversion to quantify such interpretation issues. What is a reasonable estimate for the thickness of the top layer of soil overlying the trench?