PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA ( LAB 4a )

TOPIC : PLOTTING POLES AND CONTOURING OF STRUCTURAL GEOLOGY DATA ( LAB 4a ) 1.0

OBJECTIVE To plot poles and carry out contouring of the structural geology data. 2.0 LEARNING OUTCOMES

a) b) c) d)

Students should able to use the geological compass. Students should able to measures the dip and dip direction of any planes. Students should able to plot poles of the structural geology data. Students should able to plot contour from the structural geology data. 3.0 THEORY Analysis of the orientation of structural geology data involves; 

Plotting poles representing the dip and dip direction of each discontinuity. This plot will help to identify discontinuity sets, for which both the average orientation and the scatter (dispersion) can be calculated.

The second step in the analysis is to plot great circles representing the average orientation of each set, major discontinuities such as faults, and the dip and dip direction of the cut face. 4.0 EQUIPMENT AND MATERIALS     

Equal-area for plotting poles and great circles (Appendix C) Equal-area polar net (Appendix D) Kalsbeek counting net (Appendix E) Tracing paper Pencil

5.0 PROCEDURE 

Poles can be plotted on the polar stereo net on which the dip direction is indicated on the periphery of the circle, and the dip is measured along radial lines with zero degrees at the center.



The procedure for plotting poles is to lay a sheet of tracing paper on the printed polar net and mark the north direction and each quadrant position around the edge of the outer circle. A mark is then made to show the pole that represents the orientation of each discontinuity as defined by its dip and dip direction. Poles for shallow dipping discontinuities lie close to the center of the circle, and poles of steeply dipping discontinuities lie close to the periphery of the circle.



Concentrations of pole orientations can be identified using Kalsbeek counting net. The Kalsbeek net is made up of mutually overlapping hexagons, each with an area of 1/100 of the full area of the stereonet.



Contouring is performed by overlaying the counting net on the pole and counting the number of poles in each hexagon; this number is marked on the net. These numbers of poles are converted into percentages by dividing each by the total number of poles and multiplying by 100. Once a percentage is written in each hexagon, contours can be developed by interpolation.

6.0 RESULT AND ANALYSIS 

Discontinuities pattern.



Equal-area equatorial net for plotting poles and great circles.

7.0 QUESTION AND DISCUSSION (1) Give two (2) methods to draw the structural geology data and discuss based on what situation we choose that method (each method). a. Cross section techniques - Geologic cross-section is an interpretation of a vertical section through the Earth's surface, most usefully a profile, for which evidence was acquire by geologic and geophysical techniques or from a geologic map. Cross-sections sometimes are trial sections, drawn to solve structural problems, or are drawn to supplement a fair copy map or illustrate a report. They are also drawn to site boreholes in the search for a lost aquifer or ore body. The geological cross sections drawing are not a small or trivial undertaking and methods for their generation have become sophisticated. This is because we are trying to make interpretations about the geometry of features. However, this is often the exception and skills should be tuned for cross section construction without such subsurface information.

b. Streonet Techniques - A stereonet is a lower hemisphere graph on to which a variety of geological data can be plotted. all stereonets will be plotted by hand using card stereonets and tracing paper. This is best done learning to plot by hand. In the field, for those using notebooks, it is useful to be able to draw a sketch stereonet to test a theory on the geometry of a structure being mapped. (2) Explain the type of geological structure plotted in the stereo net with the aid of diagram. - According to the geological structure that has been plotted in this experiment by the stereonet, we can determine the earth terrain such as the hill, mountain and many other earth surface that represent by the contour. There are several data that required in this experiment such as the dip directions and dip angles in the geological map. It can be plotted on polar stereonet which dip direction and dip degree is being used. In this experiment, we have 120 data to be plotted. Using the tracing paper, we have plotted 120 dotes on it which is requires focus on the plotting work or else the result will be slightly unaccurate base on the data. After the data were plotted, there are groups of plotted dotes then calculated. After that, another tracing paper was used to plot the contour. By using this kind of plotting contour method, the slope stability and the failure of slope can be determined. The failure of slope is whether planar, wedge, circular or toppling.

(3) Explain the methodology to determine the discontinuities survey data. - Discontinuities can be defined as any form of mechanical breaks or fractures within a rock mass which can cause tensile strength across the fracture planes to approach zero or even lower. To determine the discontinuities survey data, we need to collect some data and assuming some parameters in order to measure he discontinuities. To collect such data, the best tool is the geological compass. Collecting data by using geological compass is a better method because it can save a lot of time while using other method that wasting much time on calculation to find the data needed. There are another kind of method to determine the discontinuities which called Scan line Survey. Before conducting this job, there is some preliminary preparation before we do the right procedure smoothly. The discontinuities survey data sheet is prepared which is containing all of the data that we need to measure on the site. 8.0 CONCLUSION - This experiment is about plotting poles and contouring of structural geology data. From this experiment, student should be able to measure the dip and dip direction of any planes, plotting poles of structural geological data and able to plot contour from the structural geology data. In this experiment, we are using equal-area for plotting poles and great circles, equal-area for polar net, kalsbeek coutingnet, tracing paper and pencil to come to the experiment objectives.

No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Distance m 0.0 0.5 1.5 1.9 3.0 3.5 3.8 4.1 0.3 6.7 7.0 8.2 9.0 9.5 9.9 10.3 10.8 11.9 12.4 12.8 13.9 14.2 15.5 15.8 16.0 16.9 17.7 18.5 19.8 20.6 21.0 22.5 22.7 23.1 23.8 24.3 24.8 25.0 26.0 27.6 28.0 28.7 29.2 30.0 31.6 32.0 32.7 33.7 34.0 35.2

Type 1 1 1 1 3 1 1 1 1 1 1 1 1 3 1 1 3 1 4 4 1 3 1 3 1 1 1 4 3 1 3 1 1 1 4 1 3 1 1 3 1 3 1 1 3 1 1 1 1 1

Dip Direction Dip Persistence Aperture Infilling degree degree m 212 70 20 1 2 160 85 20 1 2 138 86 20 1 2 147 85 20 1 2 105 46 20 1 2 150 78 20 1 4 260 65 20 1 4 200 64 20 1 4 262 65 20 1 4 205 75 20 1 2 262 52 20 1 2 145 75 20 2 2 128 75 20 2 2 70 40 20 1 3 320 74 20 1 3 215 74 20 1 3 95 38 20 1 3 168 85 20 1 3 310 35 20 2 4 190 40 20 3 2 352 64 20 1 2 88 62 20 1 2 213 60 20 1 2 80 48 20 1 2 200 58 20 1 2 205 60 20 1 2 165 88 20 1 2 206 54 20 2 2 85 42 20 1 2 205 55 20 1 2 90 42 20 1 2 235 60 20 1 2 310 36 20 1 2 200 58 20 1 2 350 60 20 1 6 212 76 20 1 2 98 50 20 1 2 310 50 20 1 2 205 62 20 1 2 98 48 20 1 2 354 86 20 1 2 94 50 20 1 2 194 75 20 1 2 275 44 20 1 2 95 46 20 1 2 210 75 20 1 2 303 25 20 1 2 355 80 20 1 2 207 75 20 1 2 260 50 20 1 2

Roughness

water

5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 5 3 5 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 5 3 5 3 3 3 3 3 3

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

TABL E 1 ORIENTATION AND PHYSICAL CHARACTERISTICS OF DISCONTINUITIE

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continues

-

Continues

Pole data Data 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Percentage % 0.8 1.6 2.4 3.2 4.0 4.8 5.6 6.4 7.2 8.0 8.8 9.6 10.4 11.2 12.0 12.8 13.6 14.4

Scale contour 3%

6% 9%

12%

15%