Geology 107 – Study Guide for Quiz 3 – ANSWER KEY
Study Guide covers Structural Geology, Earthquakes, and Plate Tectonics
1. Label the Anticlines and Synclines on the following Block Diagram. Label the layers from oldest to
youngest on all three sides of the diagram. Be sure to label the oldest as 1 (since it was the 1st to be
deposited):
2. Label the strike, dip direction (Dip), and dip angle (Dip ) for each of the following:
N
NNW
NNE
NW
NE
50
30
62
WNW
ENE
W
E
44
WSW
Strike: NW
Dip: NE
Dip : 30°
Strike: ENE
Dip: SSE
Dip : 62°
Strike: NNW
Dip: WSW
Dip : 44°
Strike: E/W
Dip: N
Dip : 50°
ESE
SW
SE
SSW
S
12
80
5
66
Strike: NE
Dip: NW
Dip : 12°
Strike: N/S
Dip: E
Dip : 80°
Strike: WNW
Dip: NNE
Dip : 5°
Strike: NNE
Dip: ESE
Dip : 66°
25
Strike: N/S
Dip: W
Dip : 25°
Remember: Dip Direction is ALWAYS perpendicular to strike!
(regardless of the wacky way it forced me to draw some of the little dip marks)
SSE
3. Label the block diagrams with at least three layers:
(Hint: Draw the strike first. Then use the sides to show dip. The front of the block will show dip to the
east or west and the side of the block will show dip to the north or south. Remember that dip direction
has to be perpendicular to the strike (except in the case of vertical dip where it doesn’t dip N, S, E, or W
but straight into the earth).
4. What kind of fault is shown in the following diagrams? Justify your answer for each. Label the
footwall and hanging wall where appropriate.
Hanging
wall
Footwall
Left-lateral strike slip fault –
Reverse fault – the hanging wall has
There is no vertical uplift and the LEFT
moved UP in elevation relative to
side is moving toward you
the footwall (pushed together)
Footwall looks like a foot!
Footwall
Hanging
wall
Normal Fault – the hanging wall has
Right-lateral strike slip fault –
moved DOWN in elevation relative to
There is no vertical uplift and the
the footwall (pulled apart)
RIGHT side is moving toward you
5. Label the P-Wave, S-Wave, and Surface Waves on the following seismogram:
6. Based on the location of the Modified Mercalli intensity values, where is the most likely location of
the earthquake? (For hint, see Earthquakes powerpoint slide about Exercise 16.6)
The higher the numbers (Roman
numerals), the greater the intensity of the
earthquake. You can make a contour
map of the intensity, which shows the
epicenter of the earthquake (the Vs) and
the fringes of where the earthquake was
not as intense (the Is). Where was this
earthquake? Pittsburgh! 
7. Use the travel-time chart below to answer the following questions (estimate time to the nearest
quarter minute).
What is the seismometer’s distance from the earthquake’s epicenter if the S-P interval is:
a) 1 minute:
100 – 200 km
c) 3 minutes:
~500 km
b) 2 minutes:
300 – 400 km
d) 4 minutes:
(see the green dashed lines)
700 – 800 km
How long did it take for the P-wave to arrive if distance from the epicenter is:
a) 2000 km:
~6 mins, 30 secs
b) 1500 km:
~5 mins, 45 secs
c) 900 km:
~4 mins, 45 secs
d) 400 km:
~2 mins, 30 secs
(see the red dots on the P-wave curve, note that it’s difficult to get the dots to match up to the line)
How far away from the epicenter is the seismometer if it the P-wave took:
a) 5 minutes to arrive?
~1050 km
b) 6 minutes to arrive?
~1650 km
c) 5 minutes and 30 seconds to arrive?
~between 1300 and 1350 km
d) 30 seconds to arrive?
~50 km
(see the blue dashed lines)
S-Wave
P-Wave
8. Use the following Richter Magnitude scale below to answer the following questions. Show on the
chart how you arrived at your answer.
What is an earthquake’s magnitude on the Richter scale if:
a) a wave amplitude of 1 mm was experienced at a distance of 400 km?
4.3 – 4.5
b) a wave amplitude of 200 mm was experienced at a distance of 700 km?
7.5 – 7.7
c) a wave amplitude of .1 mm was experienced at a distance of 60 km?
1.6 – 1.8
d) a wave amplitude of 10 mm was experienced at a distance of 20 km?
2.6 – 2.8
e) a wave amplitude of 500 mm was experienced at a distance of 300 km?
6.6 – 6.8
(it’s hard to make the lines match up to the actual mm and km, but they’re approximate)
9. Triangulate the location of an earthquake’s epicenter using the distances provided.
a) Distance from epicenter:
Rome = 300 km
Kiev = 550 km
London = 850 km
Epicenter: Eastern Greece
Your epicenters should be in the same
general areas (it’s hard to be accurate
when drawing lines and circles on a
computer)
b) Distance from epicenter:
Oslo = 400 km
Reykjavik = 1050 km
Madrid = 550 km
Epicenter: Western Germany
10. Use the plate tectonic map on the next page to answer the following questions.
a) What type of plate boundary is the Mid-Atlantic Ridge?
Divergent
b) What type or types of crust compose the South American Plate?
Continental (landmass of South America) and Oceanic (under the Atlantic Ocean)
c) Is there a plate boundary along the eastern coastline of South America? If so, what type?
No, not along the coastline, the eastern plate boundary is in the middle of the Atlantic Ocean
d) What type of plate boundary exists between southern Spain (labeled) and northern Africa?
Transform
e) What type of plate boundary lies along the Aleutian Islands (labeled—southwest of Alaska along the
border of the Pacific and North American plates)?
Convergent
f) What geologic activity would you expect to find along the Aleutian Islands?
Earthquakes and volcanoes! They usually exist along plate boundaries where there is a lot
tectonic activity (the “Ring of Fire” surrounds the Pacific plate and is characterized by lots of
volcanoes and earthquakes)
g) Are Antarctica and Australia growing farther apart or closer together? Justify your answer.
Growing apart—there is a divergent plate boundary between the two landmasses
h) What type of boundary exists in the Middle East along the northeast border of the Arabian plate
(adjacent to the Eurasian plate)? What type of lithosphere is each plate composed of along the
boundary?
Convergent boundary—continental crust on both sides
i) If you lived in Siberia (labeled—on the Eurasian plate in Eastern Russia), would you expect to
experience many high magnitude earthquakes? Why or why not?
No, you would be relatively far away from any plate boundary where all the activity is
j) If you lived in Japan (labeled just east of Siberia), would you expect to experience many high
magnitude earthquakes? Why or why not?
Yes! The islands of Japan are a volcanic island arc system where the oceanic crust of the Pacific
plate is converging with oceanic crust of the Eurasian plate. As the Pacific plate is subducted
under the Eurasian plate, it melts at a certain depth and turns into magma. This magma rises (it’s
hot!) and creates the volcanic chain of islands that is Japan. This plate convergence creates
earthquakes along the fault plane—one of the largest earthquakes there occurred in March 2011
under the sea and resulted in a tsunami.
Divergent Boundary
Convergent Boundary
Transform Boundary
Aleutian
Islands
Siberia
Japan
Spain
11. On the following diagram, label the (1) direction of plate movement, (2) fault plane, (3) sea trench,
(4) island arc, (5) subducted lithosphere, (6) where earthquakes occur, (7) where melting of the
subducted plate occurs, and (8) where you would expect rising magma to exist.
12. The following map shows hot spot activity in southern Idaho and Yellowstone National Park. There
is an active mantle plume under the earth at Yellowstone and it has created a chain of volcanoes on
the landscape over at least the past 16 million years. The hot spot is currently below Yellowstone
Park (under the Yellowstone Caldera on the map—a caldera is a bowl-shaped structure above the
core of an ancient volcano that collapsed after it erupted). (Ma = “million years ago”)
a) What is the direction of plate movement?
Southwest
b) What is the difference in time between the oldest and youngest caldera?
16 million years
If the true distance (curved dashed line) between the youngest caldera and the oldest caldera is 300 km,
what is the rate of movement of this plate? (Show the math)
c) in km/yr:
300km
16,000,000 yrs
d) in cm/yr:
.00001875 km
yr
e) in mm/yr: .00001875 km
yr
= .00001875 km/yr
100,000
x
1000 m
1 km
x
100 cm
1m
= 1.875 cm/yr
x
1000 m
1 km
x
100 cm
1m
x
1,000,000
10 mm = 18.75 mm/yr
1 cm
If the true distance (curved dashed line) between the young caldera and the oldest caldera is 550 km,
what is the rate of movement of this plate? (Show the math)
f) in km/yr:
550km
16,000,000 yrs
= .00003438 km/yr
g) in cm/yr:
.00003438 km
yr
x
1000 m
1 km
x
100 cm
1m
h) in mm/yr: .00003438 km
yr
x
1000 m
1 km
x
100 cm
1m
100,000
= 3.438 cm/yr
x
1,000,000
10 mm = 34.38 mm/yr
1 cm
13. The mantle plume under the Pacific Plate has created a chain of volcanoes in the ocean—the islands
of Hawaii are a part of this chain.
a) Where is the oldest island and where is the youngest
island?
Oldest is northernmost, youngest is Hawaii
b) Which direction was the Pacific Plate moving from 70
to 40 million years ago?
North
c) It changed direction around 40 million years ago—
which direction is the Pacific Plate moving now?
Northwest
14. Use the following magnetic anomaly diagram to answer the questions below. The stripes show the
polarity and age of rocks at a given distance westward from their spreading center (ridge). The
eastern side of the ridge would be a mirror image of this chart. (Ma = “million years old”)
a) How old are the rocks 1000 km from the ridge?
22 – 23 million years old
b) How old are the rocks 1750 km from the ridge?
38 – 39 million years old
c) How far away from the ridge are rocks dated at 15Ma?
600 – 700 km
d) How far away from the ridge are rocks dated at 48Ma?
2100 – 2200 km
e) How far have the rocks on both sides of the ridge spread from each other over the past 20Ma?
1800 km (900 km on the western side plus 900 km on the eastern side—not shown)
f) What has been the average rate of spreading in mm/yr of the entire ridge over the past 55Ma?
The rocks on the west side of the ridge have moved ~2500 km over the past 55 million years.
Double this amount since we want to know the rate of spreading over the whole ridge, which gives
us 5000 km over the past 55 million years.
in mm/yr:
5000 km
55,000,000 yr
x
1000 m
1 km
x
100 cm
1m
x
10 mm = 90 mm/yr
1 cm