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GEO 1010 - INTRODUCTION TO GEOLOGY
FINAL STUDY GUIDE FALL 2008
The fine print: this outline is not meant to be fully comprehensive. This lists all the major topics we discussed in class, but it
does not completely cover everything involved with every topic, so use this as a guide to your notes, and to what to look at
in the text. Think of this guide as a list of topics that you should know and be able to explain or answer questions on.
The final is comprehensive but will emphasize the material we’ve covered since the third midterm. We’ve covered earthquakes
and glaciers since the third midterm; these new topics are covered by this study guide; use the midterm study guides to help
you prepare for the older material that will be on the final.
I strongly urge you to review the online handouts.
Insurance is not available for the final, but that doesn’t mean you shouldn’t do the homework. In fact, its probably all the more
reason to do the homework and arrived prepared to score well on the exam.
The final exam will be held in PS102 (section 7) or LC308 (section 8) at the UVU-scheduled time, which is available via
www.uvu.edu.
Please do not be late. I will collect all finals when the last person who arrived on time is finished, or after 1:55 minutes of time,
which ever comes first.
EARTHQUAKES.
Know the definition.
Most are caused by brittle slip on faults. Approximate maximum depth at which this happens.
Faults
1.
Hanging wall vs footwall. In a tunnel dug along an inclined (non-vertical) fault, you stand on the
footwall, hang your lantern on the hanging wall.
2.
Normal fault – hanging wall down. The Wasatch fault is an active normal fault. They form in
response to horizontal extension or stretching of the Earth’s crust, and are most common at divergent plate
boundaries.
3.
Thrust or Reverse faults – hanging wall up; most slope or dip shallowly and are called thrust faults.
Form in response to horizontal shortening or compression of the Earth’s crust and are most common at
convergent plate boundaries.
4.
Strike slip faults – are right-lateral or left-lateral. The San Andreas is _____ - lateral. Most common
at transform plate boundaries.
Elastic Rebound theory (explains how rapid slip on a fault can release a large amount of energy). Know this concept.
Wave types: P, S, surface (both Love and Raleigh waved). Know the movement of particles in disturbed medium,
speed, the order they arrive a distant site, which is most damaging.
Magnitude
How Richter magnitude is determined
What a seismometer is, basics of how one works
Distinguish intensity from magnitude (i.e., Mercalli Intensity and Richter Magnitude)
Know that Richter scale is logarithmic, and with each increment increase in magnitude waves are tenfold
larger and the EQ lasts ~ 3x longer, so a 7 releases 30 times more energy than a 6 (same for a 5 compared
to a 4, etc.).
Magnitude relates to size of fault and amount of slip – bigger fault with more slip means bigger EQ (for
example, fault length ~ 40 km = M7. M8 on 400 km fault, also can infer magnitude from amount of slip
in past earthquakes: 1 – 2 yards => M7 to M7.5; 5 to 10 yards => M8.
Modified Mercalli Intensity Scale – know general idea and its utility (can be applied to pre-seismometer
earthquakes, describes shaking at a spot, damage).
Where - epicenter, we find epicenter from P and S-wave arrival times at atleast three seismometers. Be able to do this.
Know what the hypocenter or focus is, and how for small to moderate – sized earthquakes it can be
considered to be the place where the earthquake occurred, but for large (e.g., M7 and larger) its where the
earthquake initiated.
Earthquake Hazards - shaking
Controls on Shaking Intensity
destructive shaking produced mainly from surface waves, and can be quantified by measuring peak
ground acceleration or peak ground velocity
depends on magnitude, distance from the EQ and rock type
note that the amount of damage that occurs also depends on the design and construction of structures.
The worst case scenario for ground type is loose, unconsolidated sediment that is water-saturated
because it can undergo liquefaction in an EQ. Significant amounts of liquefaction-prone
GEO 1010, Introduction to Geology Final Study Guide, Professor Bunds, Utah Valley University
sediment is present in Utah and Salt Lake Valleys. In Utah Valley, it predominates near Utah
Lake, generally west of I-15.
Building design and construction is key to their resistance to EQ Damage. Wood frame houses are
pretty good, unreinforced masonry pretty bad (including brick chimneys). Multi-story brick
buildings are very prone to damage in earthquakes. There are many layer-cake multi-story
structures in the world that tend to ‘pancake’ in earthquakes; many of these in California have
been retrofitted and reinforced for earthquake safety.
Tsunamis – Large waves. Caused by actual movement of land surface in earthquake or by landslides
triggered by earthquake. Can wash thousands of feet vertically onto land.
Landslides, fire and disease also are a significant hazards from earthquakes.
Forecasting earthquake hazards
We cannot predict earthquakes, strictly speaking. A prediction would be to accurately state when, where and
how large a future earthquake will be. Instead, we forecast the probability (chance) of a large earthquake
occurring in a future time period, along with the likely magnitude of the earthquake.
paleoseismology - when EQ’s happened in the past ; much information is taken from trenching studies. In
Utah, there have been no large EQ’s in historic time, so we depend on trenching studies for information on
past EQ’s on the Wasatch fault. In a trenching study, the location of a fault is identified, usually by the
presence of a scarp, and a trench is dug across the fault. Geologists examine the walls of the trench for soil
and sediment layers broken by fault slip during past earthquakes. The size of the earthquakes can be
estimated from the amount of slip, and the age of the earthquake can be estimated by radiocarbon dating of
the soil layers.
Then, the average of times between past EQ’s is calculated; it is called the recurrence interval or repeat time
Next, using the repeat time and the amount of time since the last EQ on the fault, geologists forecast the
likelihood of the next EQ occurring within a future time period, often the next 30 or 50 years
How big a future large earthquake may be
is estimated from the amount of slip in
past earthquakes, as well as from the
length of fault expected to rupture. For
example, slip of 1 – 2 yards on a fault
40 km in length will produce
approximately a M7 EQ, whereas; 5 to
10 yards of slip on a fault 200 to 400
km in length will produce an M8.
Geologists also use distance from the
expected epicenter & rock type to
predict shaking intensity at a location
And don’t forget:
Most Earthquakes happen at plate boundaries
Largest are at convergent
Medium at transform
Smallest at divergent (normal faults)
EARTHQUAKE HAZARD IN UTAH
Steep mountains are an indication of active faulting
Geologists look for fault scarps along the
mountain front, and elsewhere. Scarps
indicate recent (past 1000’s of years)
earthquake activity. We looked at a scarp
from the Wasatch fault on a field trip to Rock
Canyon. Examples from the mouth of Little
Cottonwood Canyon (top), and California are
shown on the right.
Trenches are dug through fault scarps to identify
ancient, buried soil layers broken by past
earthquakes.
By dating the broken soil layers, we have
identified when large earthquakes have struck
in the past 7000 years or so along the
Wasatch fault.
GEO 1010, Introduction to Geology Final Study Guide, Professor Bunds, Utah Valley University
Using this information, we can forecast the likelihood of a large earthquake occurring in a future period of time (say the
next 25 or 50 years). This is like forecasting the likelihood of a large snow storm in Orem based on how often very
large storms have struck Orem in the past, and how large the storms have been.
Several important points:
A large earthquake may (hopefully) result from a fault breaking and sliding along only one segment of the
fault’s entire length. For example, UVU is on the Provo segment (Payson to Pt. of the Mtn.) of the Wasatch
fault. SLC is on the Salt Lake Segment (Pt of the Mtn. to about the State Capitol). The segments of the
Wasatch fault are about 40 km long. The amount of movement that has occurred in past earthquakes on the
Wasatch fault, as determined from trenching studies, varies from about 1 to 3 meters. Based on the length of
the segments of the Wasatch fault and the amount of slip in past earthquakes, it is estimated that a large
earthquake on the Wasatch fault would be magnitude 7 to 7.5. An earthquake on more than one segment at
once could be M7.8 or even larger, but this is unlikely to happen.
Large earthquakes strike somewhere along the Wasatch front about every 350 years. A large earthquake strikes
on any given segment of the Wasatch fault about every 1200 to 2600 years. The Salt Lake segment last had
an earthquake about 1200 years ago, and has had earthquakes about every 1200 years, so it is due. The
Provo segment last had a large earthquake about 650 years ago so it is not ‘due.’ However, there are no
guarantees based on our current understanding of earthquakes.
Threats posed by earthquakes
ground shaking, liquefaction, landslides, fire and even disease
GLACIERS AND GLACIATION
1.
What – glacial ice, recrystallized (metamorphosed) snow, flowing under their own weight either by spreading out
(piedmont glaciers) or downhill (Alpine or valley glaciers).
2. They currently contain about 2.15% of Earth’s surface water
3. Where – Today, mostly in Antarctica and Greenland, some in Alaska. In past, wide spread on continents.
4. When – Multiple episodes of wide-spread glaciation during Pleistocene time (the past 1.6 million years or so) also periods
of glaciation throughout much of Earth’s history. Last ice age peaked about 20,000 to 30,000 years ago and ended about
10,000 to 12,000 years ago. But Earth has been non-glaciated for most of its history. During the last ice age, Utah had
alpine glaciers in the Wasatch Mountains, and Lake Bonneville filled the Utah & Salt Lake Valleys and more.
5. How: Glacial budget, zones of accumulation and wastage (melting), and flow from accumulation zone to wastage zone.
Accumulation leads to thickness, weight, recrystallization into glacial ice, and flow. (understand these concepts).
6. Types:
a. Valley/Alpine. In mountain valleys, flow downhill. Up to 100 km long, kilometers wide, couple-100 meters thick.
Think of the slides.
b. Continental (or piedmont): much bigger, hundreds, thousands of square miles/kilometers, 100’s of meters, even
kilometers (miles) thick/deep. Thickest at zones of accumulation, slowly flow outwards to zones of wastage.
7. Movement: Valley glaciers move inches to 10’s of yards per day. Can surge and move even faster – A huge valley glacier
in Alaska, the Bering Glacier, moved 1 mile in 3 weeks! Retreat by melting, not flowing uphill.
8. Landforms: Glaciers create erosional and depositional landforms because they erode and deposit large amounts of
material. They carry rocks in their base and sides, thus are like giant sandpaper and can do lots of erosion.
9. Erosional landforms created by Alpine/Valley glaciers: cirques, arêtes, horns, U shaped valleys, hanging
valleys. Can also polish rock surfaces and leave grooves that show the movement direction. Glaciers make Ushaped valleys (Big Cottonwood is classically V-shaped at bottom, U-shaped above Mill-D and Reynolds Flat).
Know this stuff.
10. Depositional landforms created by glaciers. Glaciers deposit glacial till in moraines. Moraines are the eroded
material under, in and along a glacier, both while in transport (active glacier) and when left behind after glacier melts.
Basal, lateral, medial, terminal, recessional. Sediment in a moraine is called till. Till is super poorly sorted, from
house-sized to flour-sized particles. Know this stuff. (som nice photos of moraines can be found here
http://www.swisseduc.ch/glaciers/glossary/moraine-en.html )
11. Causes of glaciation: Glaciation has 3 time periods to it. Over Earth history, there have been several periods millions or so
years long during which glaciers came and went repeatedly (i.e., multiple ice ages). During these periods, it looks like
there were 100,000 year time spans when glaciers were more abundant, but during those periods glaciers came and went
also. So glaciation has a millions of years cycle to it, a 100,000 year cycle to it, and probably a thousands or 20,000 year
cycle to it.
a. Long term, millions of years (to 100’s of millions of years): Probably caused by plate tectonics. Different
groupings of the plates create different ocean circulation patterns, which may alter climate. And when a continent
is near a pole, it is more likely to be glaciated.
GEO 1010, Introduction to Geology Final Study Guide, Professor Bunds, Utah Valley University
b.
Intermediate term, 100,000 years: Milankovitch Cycle. Variations in the Earth’s orbit (tilt of the Earth’s axis,
orbital eccentricity, and equinox precession) conspire every ~100,000 years to make the seasons significantly more
pronounced.
c. Short term, thousands of years: unclear. Possibly volcanoes or perhaps changes in Sun activity. Volcanoes
release CO2 gas, which is a greenhouse gas and can make the Earth warmer, but they also can release a lot of
ash/dust into the upper atmosphere, which blocks the Sun and can cause cooling.
12. Some specifics: Last ice age peaked about 20,000 to 30,000 years ago and ended about 10,000 to 12,000 years ago.
During this last ice age there were large lakes in the Basin and Range – Lake Lahontan in Nevada and Lake Bonneville in
Utah. Alpine glaciers were present in the high Wasatch mountains and reached the valleys at least at the mouth of Little
Cottonwood canyon.
Study questions:
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Draw a left-lateral strike-slip fault offsetting a road, and label it with motion arrows.
At what type of plate boundary are strike – slip faults common? Why? Give an example of a well-known strike-slip fault.
Draw and label a normal fault.
A t what type of plate boundary are normal faults common? Why? Give an example of a well-known normal fault.
Draw and label a thrust fault.
At what type of plate boundary are reverse faults most common?
Do faults form as a result of brittle or ductile deformation?
Explain the 3 types of waves produced by earthquakes.
Which type(s) of earthquake waves are most damaging?
Explain how the hypocenter of an earthquake is located using seismometers.
Explain, using words and a sketch, what the epicenter and hypocenter of an earthquake are.
How does the concept of a hypocenter differ for very large earthquakes, compared to small ones?
Explain how the energy of the slow movement of lithospheric plates is stored and released suddenly to produce earthquakes.
H. R. Reid developed the theory that answers this question.
What kind of plate boundary produces the largest earthquakes?
What is the largest magnitude earthquake likely to occur at a transform plate boundary?
What is the largest magnitude earthquake likely to occur at a divergent plate boundary?
How is the Richter magnitude of an earthquake determined?
How much bigger are the waves from a magnitude 6 (M6) earthquake than a magnitude 5 (M5)?
How much larger are the waves from a M9 than an M6? What about a M9 compared to an M3?
How much longer does the M6 (magnitude 6) last than the M5 (magnitude 5)?
So how much more energetic is the M6 than the M5?
How about an M8 compared to an M5 (energy)?
How is the distance to the epicenter of an earthquake determined from a seismogram?
If the P-waves from an earthquake arrive at your house 3.5 minutes before the S-waves, about how far away did the
earthquake occur? (use the figure in your textbook to solve this problem – be able to work with the figure and answer this
type of question.)
When the ‘big one’ strikes Utah, what magnitude will it probably be? On what basis is the estimate of the magnitude of a
big one on the Wasatch fault made?
What are the four crucial factors that combine to control how much damage occurs to a building as a result of an
earthquake?
What is liquifaction, what characteristics of the ground make it likely to happen, and where are these characteristics
prevalent in Utah Valley and/or the Salt Lake Valley?
How are “fault trenches” utilized in our quest to forecast earthquake hazards?
What do geologists look for when deciding where to dig a fault trench?
Can people predict earthquakes, in a strict sense?
Describe what is meant by a “probability forecast” of a future earthquake. Provide a fictitious (meaning you can make-up
the numbers) example of a probability forecast.
How often has a large earthquake happened somewhere along the Wasatch front, in the past 6000 years?
GEO 1010, Introduction to Geology Final Study Guide, Professor Bunds, Utah Valley University
33. Have there been a large earthquake on the Wasatch fault, along the Wasatch front, since western Europeans (pioneers)
arrived here?
34. What is the difference between a glacier and a snowfield?
35. Why do glaciers flow?
36. Explain how ice flow, the zone of accumulation and the zone of wastage interact in a mountain glacier.
37. How is it that glaciers retreat? Do they flow back up their valleys?
38. How do medial moraines form?
39. Be sure you can identify the following glacial landforms in a photograph or diagram: trough (U-shaped valley), cirque,
arête, horn, terminal moraine recessional moraine, lateral moraine, medial moraine.
40. The next time you drive up Big Cottonwood canyon, what two things can you look for to be able to tell how far down the
canyon the glacier moved in the last ice age? (Hints: how do glacially carved valleys typically differ from river-cut valleys?
And what do glaciers leave behind at their point of farthest advance?)
41. What might cause the climate, and thus the amount of glaciation on Earth, to vary every 100,000 years? (the answer to this
is in the study guide above and in the text)
42. Explain how in the geologic past there could have been glaciers in tropical India at the same time parts of Africa at the same
latitude (north-south position) were a desert?
43. When was the peak of the last ice age?
44. Approximately when did the last ice age end in Utah?
45. What major feature (not a glacier) that is not here today was present in Utah Valley during the last ice age?
46. When was Lake Bonneville present in Utah?
GEO 1010, Introduction to Geology Final Study Guide, Professor Bunds, Utah Valley University