6. 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.

7. What are seismic P and S waves? How do they differ? Roughly, how fast does seismic energy pass through crustal rocks?

8. The decay rate of an unstable, radioactive isotope does not depend on the quantity of that isotope present. Why? _________________________________________________________________. If the half-life of an unstable, radioactive isotope is known, then what can the ratio of the amount of parent material left to the amount of daughter product formed be used for? ___________________________ ___________________________________________________________________________________

9. Generalizing, what three general plate tectonic settings are responsible for the vast majority of earthquakes? _______________________________________________________________.
Earthquakes with foci at depths greater than about 20 km are typically referred to as “deep focus” earthquakes. Where do these occur, and why? _____________________________________ _____________________________________________________________________________.

10. 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? ________________ _______________________________________________________________________________.

11. Oceanic crust produced at mid-ocean ridges consists of a regular sequence of four geologic materials. From top to bottom, what are they? ___________________________________________ __________________________________________________________________________________.

12. 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? ____________________________________________________________________________

13. You pick up a sandstone, which, on the basis of fossils contained in it, you know was deposited in the mid-Cenozoic era, at about 30 million years ago. It has a lot of detrital biotite, and ALL of the biotite grains you analyze yield potassium (K)-argon (Ar) isotopic dates between 35 and 31 million years ago. How might you explain this observation? __________________________ ________________________________________________________________________________.

14. You pick up an igneous rock with big, fresh crystals of zircon, amphibole, biotite, and potassium feldspar. All of them, using U-Pb isotopic age determinations for the zircon, and K-Ar isotopic age determinations for the other minerals, yield statistically identical dates of 12 million years. What can you deduce from this observation? _______________________________________________________
_________________________________________________________________________________.

15. 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).

16. How can we use gravity to investigate the internal structure of our planet?

17. 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.

18. How are earthquake locations determined? What realistic assumptions are made in determining their location? What is the difference between the earthquake focus and the earthquake epicenter?

19 In isotopic age determinations, what fundamental process is utilized to quantitatively estimate the age of a particular mineral in which the decay of an unstable isotope of some element, like potassium-40, over time has occurred? __________________________________________________________________________________ ______________________________________________________________.

20. In the context of plate tectonics, continents have different kinds of margins. What is a passive margin, and provide an example. __________________________________________________
________________________________________________________________________________.
Would you expect much seismicity in a passive margin setting? ___________________ Why or why not? ____________________________________________________________.

III. Multiple Choice (30 points). There is only one correct answer.

1. What is the generally accepted age for the Precambrian/Cambrian boundary?
a. 65 million years
b. less than 6,600 YEARS
c. about 535 to 545 million years (+/- a few million years)
d. over 3.4 billion years

2. 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 540 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 entire section of sedimentary rock is tilted on its side because of extensive faulting.
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 importance 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 feature that forms by deformation of rocks?
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 overthickened 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.

14. Far from a mid-ocean ridge spreading center, what is the approximate depth to the abyssal ocean floor?

a. 1.0 kilometer
b. 10 kilometers
c. 4 kilometers
d. 100 meters
e. none of the above

15. Lithosphere plates move relative to one another at the rate of

a. kilometers/year
b. kilometers/second
c. meters/year
d. centimeters/year
e. millimeters/day

Part III. Matching (10 points)

1._______ ductile rocks a. oceanic-continental convergence
2._______ Moho b. continuously deforming; not capable of breaking
3._______ Atlantic Ocean 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._______ Nebraska f. continent/continent collision
7._______ Hawaiian islands g. plane of zero cohesion along which rocks move
8._______ Himalayas h. flows south within a continental rift
9. ______ plunging fold i. hot spot expression in a continental lithosphere
10.______ elastic rebound theory j. source of the Bandelier ash-flow tuffs
11.______ active strike-slip fault k. hot spot expression in ocean lithosphere
12.______ radiocarbon dating l. rocks capable of behaving elastically, to a limit
13.______ Andes Mountains m. map pattern shows rock contacts curving
14.______ Yellowstone n. sediment accumulation above a subduction zone
15.______ synform o. fold with limbs pointing toward each other
16. _____ fault p. less than logical place to build a dam
17. ______ accretionary wedge q. C14 decay, short half life
18. ______ convection r. stable, continent interior or craton
19. ______ outer liquid core s. formation of ocean lithosphere at mid-ocean ridges
20. ______ sea floor spreading t. impenetratable by S waves