TOPIC : FAULT BEDDING ( LAB 2b )
1.0
OBJECTIVES The end of this practical apprentice will able to : i.
2.0
To plot ground profile and rock formations from geological map – faulted bedding.
LEARNING OUTCOME At the end of the course, students should be able to apply the knowledge and skills they have learned to:
i. Students should able to plot subsurface profile. ii. Students should able to understand the geological structure in subsurface profile. iii. Students should able to understand a history of the geological area
3.0
THEORY A geological map is one, which shows in the first place, the occurrence and distribution of the rocks at the surface of the ground. Conventional sign may show certain facts of observation about them. The geological map allows the geological structure of the country to be inferred.
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Beds of rocks are bounded by bedding surfaces, which may be horizontal, tilted or bent in any form or direction. A series of beds which have been laid down regularly one on the other, and which may be treated as a whole, form a conformable series. It follows that the lower beds are the older. In such a series of bedding surfaces are parallel. Each bedding surface is usually common to two beds of rock, being the top of one and the bottom of the one next above. In the simplest case, these surfaces are planes: bedding planes. Beside that, Faults are fractures in the earth’s crust along which slippage or displacement has occurred. As a result, formerly continuous beds have been dislocated in a direction parallel to fault’s surface. The displacement may vary from a few inches or less, to many miles. When subjected to great pressure, the earth’s crust may have to withstand shear force in addition to direct compression. If the shear forces so induced become excessive, failure will result, movement will take place along the plane of failure until the unbalanced forces are equalized and a fault will be the result.
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4.0
EQUIPMENT AND MATERIALS a) Geological Map (refer to Map B )
b) Graph paper/drawing paper - A4 size c) Ruler d) Pencils e) Colour pencils (optional)
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5.0
PROCEDURES Students should learn to familiarize and observe the samples according by doing few physical tests and tabulate the results from the observation in the Table 1.1 attached for:
i.
Plot the cross-section with the horizontal and vertical scales accordingly to the scale of the geological map on a piece of graph paper or blank sheet. Refer Figure 1.1. The vertical scale is
normally exaggerated to improve visibility of the profile.
ii.
Draw a line to join the line of cross-section on the map, says A - B.
iii.
Using a blank piece of paper, mark the points of intersection accordingly between the lines with the contours respective to its heights.
iv.
Transfer the points to the cross-section profile respective to the heights of the contours.
v.
Join the points to form the profile of the ground elevation.
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6.0
RESULT AND ANALYSIS By referring to Map B,
i. ii. iii. iv. Rock Boundary
Determine the dip and strike of the coal seams. Determine the thickness of sandstone outcrop. Determine the dip and strike of the fault. Plot the rock outcrop and fault on the cross-section profile.
Dip angle
Diagram
Dip direction
AB 300 100
AB
tan θ = 240
100
190 ˚
= 25˚ 240
AB 200
BC 400 100
BLC
tan θ = 250 θ = 24˚
190 ˚
100 250
BC 300
CSBl 600
CSBL
tan θ =
100 50
190 ˚
100
θ = 63˚ 50
CSBl 500
BLC 700 100
BLC
tan θ = 240 θ = 25˚
190 ˚
100 240
BLC 600
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7.0
QUESTIONS AND DISCUSSION 1.
Explain types of fault with the aid of diagram.
The three common types of faults are normal faults, reversed fault and strike-slip fault. In a normal fault the hanging wall is displaced downward relative to the footwall. In the reversed faults the hanging wall is displaced upwards relative to footwall. If the faults dip at angles less than 45 degree the term high thrust fault is applied. Strike slip faults are the high angle fractures in which displacement is horizontal, parallel to the strike of the fault plane. There is little or no vertical movement.
Normal faults rarely are isolated fractures. Typically, a group of parallel normal faults develops a step like arrangement, or a series of fault blocks. A narrow block dropped down between two normal faults is called graben, and an upraised block is called a horst.
Strike-slip faults have a different type of movement than normal and reverse faults. You probably noticed that the blocks that move on either side of a reverse or normal fault slide up or down along a dipping fault surface.
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2.
Discuss how the fault structure was occurred based on the map B.
The fault structure occurred bas on map B is a fault which has a component of dip-slip and a component of strike-slip is termed an oblique-slip fault. Nearly all faults will have some component of both dip-slip and strike-slip, so defining a fault as oblique requires both dip and strike components to be measurable and significant. Some oblique faults occur within transtensional and transpressional regimes, others occur where the direction of extension or shortening changes during the deformation but the earlier formed faults remain active.
The hade angle is defined as the complement of the dip angle; it is the angle between the fault plane and a vertical plane that strikes parallel to the fault.
3.
If there is proposal for built dam structure on the fault area, evaluate the engineering problem that possible to be occurred.
The most engineering problem that possible to be occurred in a severe condition for a dam is when it is subjected to both ground shaking and movement of faults and other discontinuities in the footprint of the dam during strong earthquakes.
Fault slips or block movements under the dam during strong earthquakes are considered to be the most dangerous manifestations for the structural integrity of dams. Creep movements, rather slow and uniform, can be monitored and may be amenable to mitigating measures. If a fault crossing the dam site is evaluated as potentially active, the next question is what size of fault movements is to be expected, as the size expresses its damage potential. Correlation of the length of faults with earthquake magnitude and displacement along the fault, supplies such information. The coefficients for the linear least square regressions are derived from best fit procedures.
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Several authors have performed such analyses and rather significant correlations were derived. A comprehensive elaboration is given by Wells and Coppersmith (1994), based on analyzing world-wide data including hundreds of earthquakes, developing regressions of magnitude on fault rupture parameters. Quite credible correlations are obtained so that the order of magnitude of fault break displacement can be estimated.
8.0
CONCLUSION As a conclusion, we can see that fault is a fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other. This movement may occur rapidly, in the form of an earthquake - or may occur slowly, in the form of creep. Faults may range in length from a few millimeters to thousands of kilometers. Most faults produce repeated displacements over geologic time. During an earthquake, the rock on one side of the fault suddenly slips with respect to the other. The fault surface can be horizontal or vertical or some arbitrary angle in between.
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9.0
REFERENCE a) http://www.builtsense.net/topic/213-folds-faults-and-joints-geological-structures/ b) http://www.waterpowermagazine.com/features/featuredam-design-the-effects-ofactive-faults/ c) http://geology.uprm.edu/Morelock/1_image/structure.htm
Lab Report Assessment Rubric CLO 1 (Technical expertise): 10% Criteria (KI) 1 Introduction Result and analysis Question and Discussion Relevant calculation / information Conclusion Total
CLO 2 (Communication skill): 2.5% Criteria (KI) 1 Material and organisation Short and ease to understand Attractive presentation Total
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3
4
5
Weightage 0.25 0.5 0.5
Total
0.5 0.25 Total = 10%
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3
4
5
Weightage 0.17 0.17 0.16 Total = 2.5%
Total
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