EXAMPLE!!!!!!!
EPS 101 PHYSICAL GEOLOGY SECTION 001
THIRD HOURLY EXAMINATION, Tuesday, April 20, 1999
Name: _____________________________________
This
exam consists of three parts. Read the
instructions to each part and the following comment carefully. Numerical scores and preliminary grades will
be available at the end of class on Tuesday, April 27, 1999. PLEASE ATTEND!!
Thank you.
II. Short Answer Questions ( points).
1.
What is a
fault?
________________________________________________________________________
In reverse faults , regardless of the absolute
age of the rocks involved, it is always true that rocks that are relatively
___________________ are displaced on
top of rocks that are relatively ________________.
2. What is a fold? ______________________________________________________________________Why
are earthquakes NOT associated with folding?
__________________________________________________
____________________________________________________________________________________________.
3.
Regarding the figure below, Fault F1 is a moderate angle normal fault. What relationship demonstrates this? ________________ ________________________________________________________________. If you are looking to the north in this
cross section, in which direction does the fault dip? _________________In a relative sense, when did motion along this
fault occur? ________________________________________________.
4.
What is a strike-slip fault?________________________________
___________________________________
________________________________________________________________ Draw a plan view of a right-lateral
(dextral) strike slip fault oriented east-west. Show the sense of offset and label rock layers offset.
5. What
are seismic P and S waves? How do they
differ? Roughly, how fast does seismic
energy pass through crustal material?
6 .When rocks in an unfaulted area first
rupture, what happens?
7. Generalizing, what three general plate tectonics settings are
responsible for the vast majority of earthquakes? Earthquakes formed at depths greater than about 20 km are typically
referred to as “deep focus” earthquakes.
Where do these occur, and why?
8. Below
is a sketch geologic map of a part of the earth’s surface exposing folded
layers of sedimentary rock. Label these
layers, from oldest to youngest, and include appropriately distributed strike and
dip symbols to show a plunging anticline, with a direction of plunge to the southwest
(assuming north is up). If the section
of rocks, from oldest to youngest, consisted of limestones, shales, siltstones
and sandstones, arkoses, and finally conglomerates, what happened to the area
prior to folding?
9. The Earth's magnetic field is capable of
and has on numerous occasions in the past reversed its polarity. How might this phenomenon be useful in
determining the age of geologic materials? __________________
______________________________
_____________________________________________________________
10.
We discussed the fact that for “normal” continental lithosphere, the
maximum depth of earthquake focii is less than 20 km. Thus, are most earthquakes generated in the crust or mantle? _________________________ What principal factor is responsible for the
fact that most earthquakes not occur at depths below this level?
___________________________________________________ Why? _____________________________
__________________________________________________________________________________________
11.
The elevation of the abyssal ocean floor decreases, relatively smoothly,
with distance away from a mid-ocean ridge spreading center. Why is this? Food for thought: If the
rate of spreading at a mid-ocean ridge were to increase, what might this do for
the relative yet global (eustatic) level of the sea floor? How might this phenomenon be used to explain
disconformites in the continental stratigraphic record? (3 points).
12. Food for thought question (but you have
all the basics to answer it!!!). For
several decades since its “discovery” by geoscientists, Meteor Crater in
north-central Arizona was not necessarily considered the result of a young
meteorite impact. What else could it
have been? What kinds of evidence
would you look for to prove the origin of the feature, and why? (2 points).
13. How can we use gravity to investigate the
internal structure of our planet?
14.
What is heat
flow? Why does heat flow to the surface
of Earth? Identify three kinds of
settings where the flow of heat to the earth’s surface may be unusually high or
unusually low.
15.
This Thursday is EARTH DAY, 1999.
Why should, realistically, EVERY DAY be EARTH DAY??????? (extra credit,
4 points).
15.
Also Extra
credit (5 points). How are earthquake
locations determined? What realistic
assumptions are made in determinig their location? What is the difference between the earthquake focus and the
earthquake epicenter?
III. Multiple Choice (26 points). There is only one correct answer.
1. In the Grand Canyon,
a. rocks of Precambrian age are immediately
overlain by a thick sequence of lowermost Paleozoic carbonate rocks, indicating
a major sea level drop after 570 million years ago.
b. the entire Phanerozoic section of
sedimentary rocks is upside down.
c. the sequence of Phanerozic sedimentary
rocks exposed records a complex series of relative sea level changes, several have
resulted in profound disconformities marked by surface exposure in ancient
times.
d. the Precambrian "basement"
consists exclusively of a 2.5 billion year old gabbro.
e. the entire section of sedimentary rock is
tilted on its side because of extensive faulting.
f. none of the above
2.
Except at the magnetic equator, a compass needle in the northern
hemisphere points to the magnetic north pole and downward from the
horizontal. This current state of our
planet’s magnetic field is noted as
a. magnetic declination
b. magnetic reflection
c. magnetic field reversal
d. magnetic inclination
e. normal magnetic polarity
f. none of the above
3.
Our home in the Rio Grande valley is remarkable from a number of
geologic perspectives. We live in the
central part of a major rift, which means
a. an east-west trending zone in the North
American lithosphere defined by major displacement compressional structures
(i.e. reverse faults).
b. a
north-south trending zone, from central Colorado down through New Mexico is
currently extending, producing numerous geologically active normal faults. More faulting is likely.
c.
there is sound evidence that western North America will completely split
away from the rest of North America within the next five million years.
d.
west dipping
thrust faults are common throughout central New Mexico.
4. Of what significance are the terms strike
and dip?
a. the
terms are used to describe the orientation of lines in space.
b. the
terms are used to describe the orientation of planes in space; strike being the
direction of a horizontal line in the plane, and dip being the angle the plane
makes with the horizontal.
c.
they are terms used to describe the amount of offset along a fault.
d.
they are terms used to describe the absolute age of a geologic
material.
e. none of the above.
5. Strike-slip faults
a. are low-angle reverse faults
b. have mainly vertical displacement
c. have mainly horizontal movement
d. are faults on which no movement has yet
occurred
e. are characterized by uplift of the footwall
block.
6. The San Andreas fault system
a. consists of a series of strike slip faults
along which the Pacific ocean lithosphere plate is moving northward relative to
North America
b. is no longer active
c. consists of several normal faults, dipping
to the west, allowing the western margin of California to fall into the Pacific
ocean
d. consists of a series of strike-slip faults
along which the Pacific ocean lithosphere plate is moving southeastward
relative to North America
e. has resulted in numerous earthquakes with
focal depths greater than several hundred km.
7. The elastic rebound theory of faulting and
associated energy release (earthquakes)
a. requires that geologic materials rupture
with the immediate application of stresses greater than those characteristic of
surface conditions.
b. appears inappropriate for most geologic
materials.
c. explains why earthquakes occur constantly
along many faults
d. implies that for at least a period of time
geologic materials actually store energy due to applied stresses and are
strained, prior to rupture.
e. predicts that earthquakes will occur along
specific faults every hundred years, no more, no less.
f. all of the above
8. Most folding results from
a. fracturing
b. compaction
c. rifting
d. convection
e. compression
9.
Earthquake epicenters are located by
a. first arrivals of P waves from a single
station, or seismograph
b. a process of “triangulation”, involving
identifying the first arrivals from at least three stations, and making some
assumption about the actual seismic velocity from each station to the focus or
using the time difference between P and S waves to determine approximate
distances to the epicenter
c. measuring the vertical ground motion at a
minimum of three sites.
d. determining where the greatest slip along
the surface expression of the fault responsible occurred.
e. none of the above
10.
Which of the
following is not a deformation structure that shows up in rocks in the field?
a.
folds
b.
basins
c.
faults
d.
joints
e.
stratification
f.
domes
11.
Back to the Rio
Grande valley. Based on what is
currently happening in this interesting part of the western United States, what
might we expect in terms of the upper structure of the interior of our planet
beneath this north-south trending feature?
a.
a very ovethickened
crust, due to compressional forces
b.
a relatively
thin crust and a relatively shallow lithosphere/asthenosphere boundary, because
of extension and upward mantle convection beneath the rift.
c.
A unusually thick
continental lithosphere
d.
An upper
structure that is no different from that beneath eastern Kansas.
12. Interiors of continents are typically
associated with relatively low heat flow.
Why?
a.
they have
relatively thin crust
b.
the
lithosphere/asthenosphere boundary is unusually shallow
c.
the
lithosphere/asthenosphere boundary is unusually deep, implying no upward mantle convection in these
areas.
d.
The interiors of
continents are associated with unusually high topography, implying a very thick
crustal root beneath them, preventing heat from the mantle from reaching the
surface.
13. Suppose
you measure the gravity at the Earth’s surface across a topographically flat
expanse (boring) where there is a doubling of the thickness of the earth’s
crust (i.e. doubling of the depth to the Moho)
What would you find with your measurements?
a.
no change in the
gravity across the entire area
b.
an increase in
the gravity above the deep crustal “root”, because the density of crust is
higher than that of mantle
c.
a decrease in
the gravity above the deep crustal “root”, because the density of the crust is
considerably lower than that of the mantle
d.
a decrease in
the gravity above the deep crustal “root”, because the density of the crust is
considerably higher than that of the mantle.
Part III. Matching (note that in each case you
are to match a location with a process) (10 points)
1._______
ductile rocks a. oceanic-continental
convergence
2._______
Moho b. continuously deforming; not capable of
breaking
3._______
Atlantic c. crust/mantle
boundary, increase in seismic velocities
4. ______
Rio Grande d. transfer of heat by moving material
5._______
focus e. rupture location, site of release of seismic energy
6._______
Kansas f. continent/continent collision
7._______
Jemez Mountains g. plane of zero cohesion along
which rocks move
8._______
Himalayas h. flows south within a
continental rift
9. ______
Albuquerque NE heights i. presently active, magmatic arc volcano
10.______
elastic rebound theory j. source of the Bandelier ash-flow
tuffs
11.______
Glen Canyon Dam k.
surface expression of an active hot spot
12.______
Estancia Basin, east of Sandias l.
rocks capable of behaving elastically, to a limit
13.______
Andes Mountains m.
surface formed on large alluvial fan system
14.______
Yellowstone n. record of geomagnetic polarity changes with
time
15.______
Shiprock, NM o.
eroded volcanic neck
16. _____
fault p. forming Lake Powell,
rapidly filling with detritus, and soon to break,
facilitating Hoover Dam to break!
17. ______
magnetic stratigraphy
q. a glacial maximum lake some 20,000 years ago
18. ______
convection
r. stable, continent interior or craton,
Dorothy’s home
19.
______ outer liquid core s. formation of ocean lithosphere at mid-ocean
ridges
20. ______ sea floor spreading t. impenetratable by S waves