Test #1 - GEO 309/549 Structural Geology
February 20, 2007
Your Name ______
Key____________________
24 pts. (2 ea.)
1)
a)
A 10m thick bed dips at 30°. Approximately how
thick does it appear on a horizontal surface?
___20__________ m
( 0m, 5m, 7.1m, 8.7m, 10m, 14.1m 20m, 300m )
b)
A planar fault follows a single topographic contour on a map.
What does this tell you about the fault? ____Horizontal_____________________
c)
You are standing on the flank of a perfectly circular structural dome, due south from the
center of the basin. At your feet, you note a limestone bed that dips at an angle of 42°.
Give the complete strike and dip
of the limestone bed where you see it. ( ___090_____ , ___42S______ )
d)
beds
In a field mapping exercise you find a fold that is shaped like a syncline. The oldest
are in the concave center of the fold. Describe this fold ______Synformal Anticline
e)
A thin sandstone bed outcrops amidst the vegetation right at your feet. It also outcrops
at the feet of your field partner, who is standing on the next hill. She is due north of you
and at the same altitude as you.
Give two possibilities for what this observation means about the orientation of the bed.
Either the dip is.......
_________0o_______ or the strike is.....______N-S_______________________
f)
A fault with pure normal offset has a strike of N60°E and
a dip of 45° SE. The fault has a total offset of 100 m.
Give (in proper notation) the orientation of the slickenlines ___150__ ,___45S_
What is the rake of the slickenlines? ____90___
To the nearest meter…
How large is the heave? _____71______m How large is the throw?_____71______m
10 pts. (2 ea.)
2)
A fault plane is oriented (N50°W,vertical).
Motion on the fault is a combination of dip-slip and strike-slip.
Slickenlines have a rake of 35°NW.
The plunge of the slickenlines is _____35___________
(0°, a bit less than 25°, 25°, a bit more than 25°, a bit less than 35°, 35°, a bit more than 35°, 90°)
The bearing of the slickenlines is ______310____________
(000°, 025°, 050°, 055°, 140°, 230°, 270°, 310°, 350°)
The strike-slip component of fault motion is ________> DS________________
(larger than the dip slip, equal to the dip-slip, smaller than the dip-slip, can’t tell)
If the total offset on the fault is 100 meters, the strike-slip component is: ___82______ meters
The dip slip component is ______57____ meters.
16 pts.
3)
cos  sin 
Using a rotation tensor of R  
, a vector with a starting orientation of x=1,
sin  cos  
y=0 is rotated by 45° counterclockwise. This vector has a new orientation of x=___0.71
y=__0.71__.

The plates on the earth are rigid spherical caps and their respective motions can be
described by axes of _Rotation that pass through the _Center__ of the Earth.
The transform faults at mid-ocean ridges define _______ _________, or lines of latitude
about the pole of rotation.
In a 3-D case, there are __3___ principal axes of strain.
A principal axis of strain can be thought of as a direction along which the starting vector
and ending vector are in (a) the same direction (b) differing directions (c) a ninety degree
orientation from one another (d) an angular separation of one radian. ____A___
18 pts. (2 ea, plus 2 for work shown on map)
4)
Below is a topographic map (elevations in meters), showing the trace of a limestone bed across
the surface of a hill. There is a fold. (You MAY note TWO possible solution. Choose the solution
where the strikes of the beds on the limbs of the folds are more N-S oriented (as opposed to E-W
oriented)
What (within 15° each) are the strike
and dip of the bed on one side of the fold? _000_____, ____45E__
..............and on the other side of the fold they are: ___180__, ____45W__
If we define the fold axis as the line separating the two dip domains, then what (within 15°
each) are the bearing and plunge of the fold axis? __000____, ___000___
Look at the strike lines you drew. The fold could have been produced by (a) east-west
extension (b) east-west compression (c) N-S compression (d) N-S extension (e) strike-slip
deformation ___B___
SHOW ALL YOUR WORK ON THE MAP, and INDICATE THE FOLD
AXIS
600
500
400
300
200
100
0
200
400
scale in meters
600
16 pts. (2 ea.)
5)
In an area with very little topography, a fold plunges at a SHALLOW angle.
All beds dip at only shallow angles.
In the fold is a bed that appears as a thick black curve on the map below.
There is also a vertical dike that appears as a shaded line striking northwest-southeast.
The bed and the dike are both cut by an east-west striking fault that dips STEEPLY.
Beds are NOT overturned.
Is the fold a syncline or an anticline? ___Anticline____. Which way does it plunge? ___E___
(N,E,S,W)
If the fault is strike-slip, it is __Right_-lateral.
Now, look carefully at how the bed has been offset vertically..........
If the fault is a normal fault, then
which side has dropped downward? The ____North_____ side.
( north , south )
Therefore, if it is a normal fault, which way does the fault dip? ____North_____
( north , south )
EXPLAIN below in A FEW WORDS the best clue that it’s a normal (and not strike-slip) fault:
____________________________________________________________________________
Where are the rocks older at the surface, X or Y? ___Y_______
Where will you find the bed if you drill vertically? _______X______________
( X , Y , X and Y , neither X nor Y )
16 pts.
6)
For an exposed section of the San Andreas Fault, one would expect to see slickenlines that have
a rake of _________0_____(0°, 30°, 45°, 90°, 130°). The plunge on these slickenlines are
expected to be _______0________(0°, 30°, 45°, 90°, 130°)
The forces that give rise to the significant permanent strains (deformation) with the Earth’s
crust arise from: (a) lunar tides (b) relative plate motions (c) solar wind (d) centrifugal force (e)
ocean and glacial loading.
Cross-sections are usually ___Perpendicular__ to strike, so as to show ___True____ dips.
If one observes flat beds on a vertical cliff face, then either the beds are ___Flat_____ or the
direction perpendicular to the cliff face is the direction of __True___ _____Dip___.
Apparent dip is always _____< or =_______ true dip. Moreover, the plunge of a slip vector is
always ___< or =__________ the rake of the slip vector.
(greater than, less than, greater than or equal to, less than or equal to )