Structural Geology (Geol 4013/6013)/50

Lab Exercise 6Name: ______

Questions (50 pts), 50 pts for other graphs and plots.

  • Determination of fault slip line vector (net slip)
  • Piercing Point
  • Faults and principal stresses

Study Chapter 8 and 10 of the Lab Manual by Donal M. Ragan: “Structural Geology, an Introduction to Geometrical Techniques”.

Use the following color scheme: Use a redpencil to draw the fault plane on the stereonet and map.
Use different dark colors for other lines (e.g., vein, dike, bed, net slip, strike-slip, dip-slip)!

Solve the problem on page 174, using Figures 8.12 & 8.13.
Follow the instruction for the problem on Page 174 in section 8.5 of Chapter 8, and answer the questions.

Plot the fault (in red) and vein (in blue) as great circles!
Label the line of their intersection as ‘i’.
  1. What is the attitude of the intersection line, i?
  1. 196, 25 b. N16E, 26 c. 320, 14 d. 029, 25 e. 081, 12

  1. What is the pitch of the line of intersection (i)?
a. 16S b. 16S c. 30N d. 42S e. 17S
On a graph paper, draw a horizontal E-W oriented line (trace or strike of the fault with the same length as the length of the fault on Fig. 8.12 (i.e., 5 cm). Mark point A on the line.
From point A, draw the cut-off line of the vein on the footwall, with a pitch of 30 from N (see Fig. 8.13).
From point A, draw the 100 m (18 mm) long normal slip (D) perpendicular to the trace (strike) of the fault.
D intersects the cut-off line on the hangingwall.
From the intersection point, draw a line parallel to the footwall cut-off line, back to intersect fault’s strike!
Locate point B where the vein is exposed on the east side of the fault (i.e., the hangingwall).
From point B, draw the outcrop trace of the vein, in the eastern side of the fault, as a line parallel to the vein in the western side (see Figure 8.13b)
  1. How much is the strike separation (i.e., line AB)?
  1. 67 m b. 24 m c. 82 m d. 120m e. 181m

Problem on page 177(Use Figure 8.14). Follow the instruction for the problem on page 177, and answer the questions. Scale: 10.5 mm = 200 m.

Plot the fault (in red) and the bed (in blue) as great circles. Label them!
Label the intersection line as ‘I’.
Plot the slickenside (D) (see Figure 8.14b)
  1. What is the pitch (rake) of the bed on the fault?
  1. 48S b. 34N c. 41N d. 17S e. 55S

  1. What is the pitch (rake) for the striations on the fault?
  1. 35S b. 36S c. 82N d. 70S e. 17S

Mark the slickenside as ‘D’ on the fault great circle.
Draw a horizontal line on your graph paper, with the same length as that on Figure 8.14a, to represent the trace (strike) of the fault (see Figure 8.14c). Mark points A and B on this line! Note: B is north of A!
At point A, draw the footwall (FW) cut-off line for the bed using its pitch.
At point B, draw the hangingwall (HW) cut-off line for the bed using its pitch
From point A, draw the slip line D (using its pitch), to intersect the hangingwall cut-off line. Measure the length of D.
  1. How much is the amount of net slip (D)?
  1. 117 m b. 120 m c. 68 m d. 98 m e. 380 m

  1. How much is the strike-slip (SS)?
  1. 95 m b. 102 m c. 58 m d. 99 m e. 137 m

  1. How much is the dip-slip (DS)?
  1. 235 m b. 100 m c. 62 m d. 362 m e. 69 m

  1. What is the sense of slip?
  1. Left-lateral normal b. right-lateral reversec. right-lateral normal d. left-lateral reverse e. pure reverse

Problem on page 178(use Figure 8.16!). Carefully read the problem.

Carefully copy Figure 8.16 onto a graph paper.
Plot the fault, bed, and vein on the stereonet.
  1. What is the pitch of the bed on the fault?
  1. 41N b. 67S c. 17S d. 28N e. 54S

  1. What is the pitch of the vein on the fault?
  1. 12S b. 74N c. 64S d. 36N e. 45N

Determine the piercing points x and y, on the footwall and hanging wall, respectively, by using the pitch angles and drawing the cut-off lines for the vein and bed at points A1, A2, B1, and B2.
Connect x to y, and determine the amount of slip, using the scale.
  1. What is the amount of the net slip?
  1. 77 m b. 130 m c. 88 m d. 240 m e. 180 m

  1. What is the pith for the net slip (NS) on the fault?
  1. 73N b. 34S c. 12S d. 34N e. 26N

  1. How much is the strike-slip (SS) component of the slip?
  1. 24 m b. 34 m c. 60 m d. 82 m e. 29 m

  1. How much is the dip-slip (DS) component of the slip?
  1. 41 m b. 56 m c. 62 m d. 220 m e. 23 m

  1. What is the sense of slip?
  1. Right-lateral normal b. right-lateral reverse c. left-lateral normal d. left-lateral reverse
    e. pure normal

/10 pts Attach your stereonet and graph paper!

Part II- Do the following from the 8.13 Exercises on page 197 (Chapter 8) of the Lab Manual:

Problem 1 on page 197. If a normal fault, oriented: 000, 60W, cuts a plane: 270, 30N, and shows a left separation of 100 m, find the net slip. Use the 4 cm = 100 m scale for your graph paper!

On the upper part of a graph paper, draw the trace of the N-S fault and the E-W displaced plane (separated by 4 cm at points A and B).
Point A is the hangingwall exposure, and point B is the footwall exposure!
Plot the fault, and the plane on stereonet
  1. What is the pitch of the plane on the fault?
  1. 24S b. 17N c. 26S d. 34N e. 45S

On the lower part of the same graph paper, draw a horizontal line, representing the strike of the fault, and mark points A and B, 4 cm apart.
Mark the hanging wall (HW) on the dipping side of the fault.
Draw the cut-off lines for the plane at points A and B, using the pitch.
Use solid line for the FW and dashed line for the HW cut-off lines.
Since the fault is normal, the net slip must be perpendicular to the strike of the fault. Draw a line at point B, across the strike to intersect the cut-off line for the hangingwall. This is the net slip!
  1. What is the amount of net slip?
  1. 34 m b. 67 m c. 48 m d. 21 m e. 97 m

Attach your stereonet and graph paper!

Problem 2 on page 197 (Figure 8.44)
Fault: 270, 60N, intersects Plane 1: N45W, 30NE, and Plane 2: N50E, 45NW.

Plot the fault (in red) and Plane 1 (in blue) and plane 2 (in green) on the stereonet
  1. How much is the pitch for Plane 1?
  1. 12 E b. 45W c. 32E d. 16W e. 54W

  1. How much is the pitch for Plane 2?
  1. 45 E b. 36E c. 62E d. 36W e. 53W

On the lower part of the graph paper, draw an E-W line to represent the strike of the fault. Mark points A, B, C, and D on to correspond their position on Figure 8.44.
  1. Which side is the hanging wall?
  1. Southern side b. Northern side

Points A and B are the exposures on the HW and points C and D are exposures on the FW
Draw the cut-off lines for the two planes. Use dashed line for the HW cut lines and solid lines for the FW cut-off lines
Intersect the dashed lines. Intersect the solid lines.
Connect the two intersection points. This is the net slip!
  1. What is the pitch (acute angel) of the net slip?
  1. 42E b. 31W c. 18W d. 25E e. 64W

  1. What is the orientation (trend, plunge) of the net slip?
  1. 134, 15 b. 259, 16 c. 089, 24 d. 287, 26 e. 056, 56

  1. What is the magnitude of the net slip (NS)?
  1. 270 m b. 310 m c. 148 m d. 220 m e. 184 m

  1. What is the slip-based name for the fault?
  1. Left-lateral oblique normal b. right-lateral oblique normal c. left-lateral oblique reverse d. right-lateral oblique reverse e. pure reverse

  1. What is the magnitude of the strike-slip (SS) component?
  1. 97 m b. 45 m c. 111 m d. 158 m e. 86 m

  1. What is the magnitude of the dip-slip (DS) component?
  1. 66 m b. 26 m c. 95 m d. 120 m e. 140 m

/10 pts Attach your stereonet and graph paper!

Part III. Chapter 10 Exercises, Page 267.
Problem 1 on page 267.

Two conjugate faults have attitudes: Fault 1: N30E, 70W and Fault 2: N10W, 60Eand.
Determine the orientation of the principal stresses at the time of the formation of the two faults.

Plot the two faults (in red) on the stereonet.
Label them as Fault1 and Fault2.
  1. What is the orientation of the line of intersection of the two faults (i.e., the intermediate principal stress axis 2)? Label and mark it with the 2 symbol!
  1. N46E, 20 b. N23W, 14 c. N14E, 35 d. S35E, 35 e. S56W, 43

Having the 2 axis, find the 13 plane (perpendicular to it).
This is the ‘Movement plane” or the ‘M-plane”.
  1. What is the orientation of the maximum principal compressive stress (1)?
    Label and mark it with the 1 symbol!
    Note: 1 is on the acute bisector of the two faults, on the M-plane!
  1. S3W, 55 b. N87E, 30 c. S58E, 23 d. S15W, 68 e. S36W, 37

  1. What is the orientation of the minimum principal compressive stress (3)?
    Label and mark it with the 3 symbol!
    Note: 3 is on the obtuse bisector of the two faults, on the M-plane!
  1. N87E, 5 b. N3E, 22 c. S12E, 15 d. S68W, 78 e. N79W, 4

Label the two intersections of the M-Plane with the two faults as ‘SL’ to represent the slip lines.
  1. What is the angle of , between 1 and the two slip lines (SL)?
  1. 12 b. 42 c. 31 d. 20 e. 60

  1. What is the angle of the internal friction (i)?
    Note: From the Mohr circle we have: i +2 = 90.
  1. 39 b. 28 c. 35 d. 15 e. 20

  1. What is the sense of slip on Fault 1?
  1. Left-lateral reverse b. right-lateral reverse c. left-lateral normal
    d. right-lateral normal e. pure normal

  1. What is the sense of slip on Fault 2?
  1. Left-lateral reverse b. right-lateral reverse c. left-lateral normal
    d. right-lateral normal e. pure normal

Attach your stereonet

Problem 2 on page 267.

Fault 1 and Fault 2 are conjugate. Their traces on a horizontal plane are: N25W and N82W, respectively.
The pitch of Fault 1 and Fault 2 on plane 1, oriented: N10E, 70E, are 18S and 48N, respectively.
The pitch of Fault 1 and Fault 2 on plane 2, oriented: N76E, 80N, are 30W and 26E, respectively.

Plot the horizontal traces of the two faults, by putting 1 and 2, at N25W and N82W on the primitive.
Plot Plane (face) 1 and Plane (face) 2 as cyclogram (great circle).
Draw the pitch of the two faults on Plane 1 and Plane 2.
Mark these with dots as 1 and 2, respectively.
Draw the cyclogram(great circle) of Fault 1 (connecting 1 and 1) and Fault 2 (connecting 2 and 2).
  1. What is the orientation of the line of intersection of the two faults, i.e., 2?
Label and mark it with the 2 symbol!
  1. N13W, 34 b. N60W, 20 c. N35E, 24 d. N78W, 22 e. N12W, 67

Draw the M-Plane perpendicular to 2.
  1. What is the orientation of the maximum principal compressive stress (1) on the acute bisector of the two faults?Label and mark it with the 1 symbol!
  1. N12W, 14 b. S88E, 50 c. S23W, 7 d. N33E, 7 e. N38W, 9

  1. What is the orientation of the minimum principal compressive stress (3) on the obtuse bisector of the two faults?Label and mark it with the 3 symbol!
  1. S21E, 14 b. S68W, 51 c. S35, 40 d. N33E, 7 e. S67E, 70

Label the principal stress axis on the stereonet as 1, 2, and 3
  1. What is the angle of internal friction (i)?
a. 16 b. 22 c. 34 d. 30 e. 37
  1. What are the senses of slip on Fault 1?
  1. Left-lateral reverse b. right-lateral reverse c. left-lateral normal
    d. right-lateral normal e. pure reverse

  1. What are the senses of slip on Fault 2?
  1. Left-lateral reverse b. right-lateral reverse c. left-lateral normal
    d. right-lateral normal e. pure reverse

/10 pts Attach your stereonet

Problem 3 on Page 268 (note the error in the book!)

Slickensided normalfault is oriented: N32E, 60NW (SW is wrong!).
Striations (slickensides) are oriented: 54, N23W.
Determine the orientation of the three principal stresses at the time of faulting.

Plot the cyclogram of the fault and the slickenside () on it. Plot the pole to the fault and mark it with a cross ().
Facts: The striations () must be:
on the fault! On the M-Plane, and 90o to the intermediate principal axes (2)
2 must also be on the fault plane!
The M-plane contains the pole to the fault () and the striation ()
Draw the M-plane by connecting the pole to the fault () and striations () on a great circle
Pole to the M-plane defines 2.
Label and mark it with the 2symbol!
Assume that 1 is at about 30o to the fault (i.e., ≃ 30).
Mark it with the 1symbol!
Find 3 at 90o to 1. Mark it with the 3symbol!
  1. What is the orientation of 1 (i.e., 1)?
  1. S32E, 14 b. S36W, 51 c. S51, 40 d. N23E, 7 e. N34E, 72

  1. What is the orientation of 3 (i.e., 3)?
  1. S50E, 2 b. S68W, 25 c. S35, 14 d. N13E, 9 e. S67E, 78

  1. What is the orientation of 2 (i.e., 2)?
  1. S44E, 44 b. S42W, 17 c. S76, 24 d. N33E, 5 e. S56E, 61

  1. What is the angle of internal friction (i)?
    Note: i+2 = 90
  1. 24 b. 30 c. 42 d. 36 e. 16

  1. What is the sense of slip on the fault?
  1. Left-lateral reverse b. right-lateral reverse c. left-lateral normal
    d. right-lateral normal e. pure normal

Attach your stereonet

Problem 6 on Page 268

Given:The cohesive strength, Co = 38 MPa. Angle of internal friction, I = 33o, and
1 remains a constant 100 MPa.

  1. What will be 3 at failure?
  2. Under the same conditions, if anexisting fracture, with an angle of sliding friction of s = 33o, is oriented 45o to the 1, which will occur? Fracture or slip?
  3. If the existing fracture, is oriented 55o to the 1 direction, which will occur? Fracture or slip?

On a graph paper, plot the Mohr circle, using the scale: 1 cm = 10 MPa. Label everything!
Plot the straight, solid line (s= Co + in) from theCo = 38 MPa intercept, with a positive slope of
I = 33ofrom the naxis
Start with 1 = 100 MPa and put the pin of your compass (i.e., the center of the circle) on the x axis, and with trial and error try to make a Mohr circle to go through 1 = 100 MPa while touching the envelope.
If it does not work, reduce the 3 until the circle touches the envelope and goes through the 1 = 100 MPa. When that happens, read 3.
  1. Part (a). What will be 3 at failure?
  1. 20 MPa b. 12 MPa c. -13 MPa d. -31 MPa e. 23

Plot a straight, dashed line (s= sn) from the origin, with a positive slope of s = 30ofrom the n axis.
  1. Part (b). What will occur first if the angle of friction is 30o for a fracture inclined 45o to 1
    (i.e., if  =  = 45)? Fracture or slip?
  1. Fracture b. Slip

  1. Part (c). What will occur first if the fracture is inclined 55o to 1, fracture or slip
    (i.e.,  = 55, or =  = 35)?
  1. Fracture b. Slip

  1. Which line is steeper? The s= Co + in) or s= sn?
  1. The coulomb criterion line b. The frictional sliding criterion

  1. What is the 2 angle for part c?
  1. 70o b. 35o c. 210o d. 55o e. 80o

/20 pts Attach your Mohr circle and failure envelope

Structural Geology (Geol 4013/6013)Lab 6. Page 1