ES304 Self-assessment Test, Page 3

The questions in this test are similar to those in the sample paper for the end-of-semester assessment. However, the actual assessment will have few multiple-choice questions, and many single-word answer questions compared with this version.

If you have difficulties with any of the answers, don't hesitate to see or email me.

In each section, either choose answers with the radio buttons, or from the pulldown menus, then press the "submit" button to have the test scored and to get some feedback. At this time there is no record of your performance retained on the system.

 

Test 1

Test 2

Test 3

Test 4

Questions about rock and mineral properties will usually be one-word-answer style in the final paper:

First part

The choices in some of these menus may sometimes seem strange or unlikely—but most of them have been served up as answers in exams, so don't scoff too loudly!

 

1
 What are the units in which resistivity is measured?  
2
 Which of these materials has a relatively low resistivity?  
3
 Archie's Law at its simplest relates rock or formation resistivity to pore fluid resistivity and...?  
4
 The resistivity of a sandstone bed is seen, in measurements in a borehole, to decrease from top to bottom. What might this mean?  
5
 Black shale beds often have low resistivity. Why?  
6
 The resistivity of a bed hosting conductive-mineral ore will be unusually low if the ore is ...?  
 
 

Second Part

Remember that you also learn basic information in the practical class exercises, and this all becomes part of your knowledge base.

 

1
 Resistivity measurements require current to be injected into the ground through electrodes. What limits the current?  
2
 In resistivity sounding, why is there a larger error in measurements made at large spacings?  
3
 If resistivity measurements are repeated over a period of hours at the same observation point, what is the chief source of variation in the resistivity measurements?  
4
 You are planning an electrical sounding to recognise layering down to perhaps 100m. What is the maximum electrode spacing you would budget to use?  
5

You are carrying out an electrical sounding, and have increased the array spacing in the following steps:
1 m - 1.5 m - 2 m - 3 m - 5 m - 8 m - 10 m.

What would your next spacing most likely be?

  
6
 A Wenner or Schlumberger sounding is carried out by expanding the electrode array along a line. Two such soundings are carried out, each on a line at right angles to the other (frinstance, NS and EW) but with centres coincident. Why might the resistivities interpreted differ (even if the layer thicknesses are the same)?  
 
 

Third Part

Some of the questions in these pages haven't been covered in lecture class or in practical work. They are very unlikely to be part of an assessment (unless there is some basis in the subject for you to work from), but try and work through the answer anyway. If for no other reason than you might encounter an unexpected question in the final exam.

 

1
 Electromagnetic measurements of rock resisitivity are often easier to carry out than direct-current resistivitymeasurements. Why?  
2
 In frequency-domain electromagnetic (FDEM) exploration, what controls the depth of penetration on a given geological section?  
3
 Time-domain electromagnetic (TDEM) methods have become important because they ...?  
4
 The Audio Frequency Magnetic (AFMAG) technique is a passive electromagnetic method in which measurements are made of variations in the propagation of electromagnetic waves from ... ?  
5

Frequencies used in electromagnetic exploration of the upper crust are typically in what range ...?

  
6
 Dowsing is practiced in many areas to locate subterranean streams, and sometimes gold and precious gems. Typically the dowser carries one or more sensors and observes their response. What are the most effective dowsing sensors?