GLY 220: Physical Geology Exam 3 Review Sheet What to expect Exams for GLY 220 are composed of 50 multiple-choice questions. The only thing you need to bring to the exam is a Number 2 pencil with an eraser. You do NOT need to buy scantrons; I provide these for you free of charge. No calculators are required or permitted. The exam will not be administered until everyone has left personal items (backpacks, purses, cell phones, etc.) at the front of the class, cleared their desk, and stopped talking. You may keep cell phones in your pocket, but if they are seen at any time during the exam, you will automatically receive a zero. When you are finished, please turn in both your exam and answer sheet to me at the front of the class. Material covered on the exam Exam 3 will cover ALL MATERIAL discussed in lecture from “Earthquakes” to ”Plate Tectonics” (only through Transform Plate Boundaries, which we covered on April 8). “All material covered in lecture” includes everything we discussed in class, including any videos, whether or not it appears on the PowerPoints. For example, some slides in my PowerPoints are photographs or maps without much accompanying text; what I said in class while those slides were on the screen is fair game on the exam. I hope you took good notes of that material! In the bulleted listing below, I list what a summary of the topic you should focus on for Exam 3. Some students misunderstand the purpose of this list, so I have added these important disclaimers: 1. THE BULLETED ITEMS ARE NOT QUESTIONS YOU WILL SEE WORD FOR WORD ON THE EXAM; they are merely a TOPICAL SUMMARY of the material that I think is most likely to appear on the exam. Most questions will test your knowledge, and to a lesser extent application, of this material. Other questions will test your application of skills learned during this course (i.e., how to recognize various geologic features from photographs, etc.). 2. The questions on the exam are MORE DETAILED than the topics listed below. Remember, EVERYTHING discussed in class is fair game, including DETAILS. To help you appreciate this, I have included 15 sample questions from last year’s exam at the end of this review sheet (you can find the answers to these questions yourself). These questions will probably not occur on this year’s exam, but who knows, I may just get lazy and use them again. 3. Not everything on the exam will necessarily come from this review sheet, and not everything on this review sheet will be on the exam.
Earthquakes • How is the mechanical behavior of rock similar to that of a rubber band? Be able to describe the elastic rebound theory of earthquakes. • Know terminology related to earthquakes: epicenter, focus, fault plane, scarp • What are the four types of seismic waves? What are their relative velocities and motions? • How does surficial geology affect the intensity of surface waves? How was this important during the 1989 Loma Prieta earthquake in the Bay Area of California? • How does a modern seismograph work? Why are multiple instruments needed to completely record the location of an earthquake? • What kind of observations is the Mercalli intensity scale based on? • How many seismic stations are needed to locate an earthquake epicenter? • How is the Richter magnitude determined for an earthquake? How is it different from the Mercalli intensity?
2 Crustal Deformation • What is stress? • What are the various types of stress? Which kinds of stress cause deformation (strain)? Which kind causes small changes in volume, but does not deform rocks? • What is the difference between brittle and ductile deformation: what variable controls which kind occurs? • What is the difference between a joint and a fault? • What are the three types of faults, and how are they related to the three types of directed stress? • What is meant by the “hanging wall” and the “footwall” of a fault? • Be able to identify fault types from diagrams or photos. • What are the various kinds of ductile deformation that we discussed in class, and what kind of stress causes them? • Be able to distinguish between a syncline, anticline, monocline, dome, and basin, either from photos or diagrams. Earth’s Interior • What are some direct and indirect methods used to study the Earth's deep structure? • What are the most abundant chemical elements in the Earth? • What are some physical properties, thicknesses, and compositional/mineralogical characteristics of the various regions of the Earth? For your own study, be able to sketch Fig. 2.14 (you do not need to know exact thicknesses or temperatures) • What probably causes the seismic discontinuities at 400 and 670 km depth? • Where is the mantle partially molten? • What are some major differences (age, composition, density, thickness, mechanical behavior, etc.) between the crust and mantle? between continental crust and oceanic crust? between the asthenosphere and lithosphere? • Which layer(s) are convecting? fairly rigid? The Discovery of Plate Tectonics • What evidence did Wegener use to support his theory of continental drift? • Why wasn't his theory accepted soon after he presented it? • What were some of the oceanographic discoveries that helped resurrect Wegener's theory during the mid-20th century? • What is paleomagnetism? How do igneous rocks become magnetized? • How is the Earth's magnetic field generated? What is believed to cause reversals of the Earth's magnetic field? • How are studies of volcanic rocks on land used to construct the geomagnetic reversal time scale? • How are magnetic anomalies used to date the ocean floor? • Where are the youngest portions of the ocean floor located? the oldest? • Why is there no oceanic crust around today older than ~200 million years? Plate Tectonics • Approximately how many lithospheric plates are there, and how were they discovered? • What is the difference between an active and a passive continental margin? For your own study, be able to sketch a simplified passive margin (Fig. 4.4). • What are the three types of plate boundaries? o be able to identify important features associated with a particular type of plate margin o be able to describe the geologic activity at a particular type of plate margin o be able to list some geographic examples of a particular type of plate margin o for your own study, be able to sketch a simplified cross-section through a mid-ocean ridge (Fig. 4.8) and a continental margin subduction zone (Fig. 4.15) • What causes volcanism above subduction zones? • What happens to oceanic lithosphere as it ages? • How do oceanic fracture zones work? Where along their length does active faulting occur?
3 SAMPLE QUESTIONS Here are 15 sample questions from last year’s exam. Notice how most of these questions correlate with material on the list of topics above, but are MORE DETAILED. These questions will probably not occur on this year’s exam, but I am not ruling anything out, either. 1.
P-waves a. are a type of body wave b. propagate through rocks outward from the focus of an earthquake c. involve compressive motions of particles within rock materials d. travel faster than Love waves e. all of the above
2.
During the 1989 Loma Prieta earthquake in the Bay Area of California, the most damage occurred to structures that were built a. near the San Andreas Fault in San Francisco b. near the Hayward Fault in Oakland c. on soft sediments near San Francisco Bay d. on hard igneous and metamorphic rocks in the mountains
3.
What is the minimum number of seismic recording stations required to pinpoint the epicenter of an earthquake? a. 1 b. 2 c. 3 d. 4
4.
Cracks in rocks along which no discernable relative motion has occurred are called a. faults b. monoclines c. unconformities d. joints
5.
Faults in which the hanging wall has moved down relative to the footwall are a. thrust faults b. reverse faults c. strike-slip faults d. normal faults
6.
Strike-slip faults are caused by a. tensional stress b. compressional stress c. shear stress
7.
Foliation in metamorphic rocks results from a. brittle b. ductile
8.
What type of data tells us the most about the structure of the Earth’s deep mantle and core? a. xenoliths in volcanic rocks b. seismic waves from distant earthquakes c. deep drilling d. erupting magma e. tectonic uplift of originally deep rocks (in mountains)
deformation at high temperatures and pressures.
4 9.
The changes in seismic velocity which occur at 400 and 670 km depth within the Earth probably reflect a. changes in rock composition b. changes in density due to the olivine crystal structure c. changes in density due to the presence of significant quantities of magma
10. The distinction between the lithosphere and asthenosphere is made on the basis of a. composition b. mineral content c. physical behavior d. age 11. Regions of the sea floor with positive magnetic anomalies were formed during times when Earth’s magnetic field a. was exceptionally strong b. was exceptionally weak c. had normal polarity d. had reversed polarity 12. Oceanic lithosphere a. is the same thickness throughout an entire ocean basin b. gets thicker away from a mid-ocean ridge c. gets thinner away from a mid-ocean ridge 13. What process is primarily responsible for the origin of volcanoes above subduction zones? a. friction as both plates move past each other; this melts portions of both plates b. release of water from the subducting plate; this melts portions of the upper plate c. the subducting plate gets hotter as it descends and it eventually melts d. generation of hotspots in the deep mantle far below the subduction zone e. this is where molten material from the Earth’s outer core comes to the surface 14. When two pieces of continental crust converge towards one another, the final result is a. a large mountain belt b. destruction of an ocean basin c. a larger continent with a tectonic suture between the two original pieces d. all of the above e. none of the above 15. The San Andreas Fault in southern California is an example of a a. continental rift b. transform plate boundary c. divergent plate boundary d. passive margin
5 SOME TERMS TO KNOW Since the exam is multiple choice, you will NOT need to write a full definition for any of these terms. However, you should know what these things are to the degree that we talked about them in class. Many of these terms can also be found in the glossary in the back of your textbook. focus epicenter scarp body wave P-wave S-wave surface wave Rayleigh wave Love wave seismic amplification Mercalli intensity Ritcher magnitude seismograph liquefaction tsunami stress confining stress directed stress compression tension shear strain brittle ductile joint hanging wall footwall normal fault
graben drag fold reverse fault thrust fault window klippe strike-slip fault anticline syncline monocline dome basin xenoliths seismic refraction core mantle lower mantle transition zone upper mantle oceanic crust continental crust seismic discontinuities convection lithosphere asthenosphere continental drift (e.g., Wegener’s idea) Pangea
Gondwana mid-ocean ridge magnetic anomalies magnetic reversal geomagnetic reversal time scale seafloor spreading lithosphereic plate active (continental) margin passive (continental) margin divergent (plate) boundary convergent (plate) boundary transform (plate) boundary pillow basalt black smoker continental rift subduction zone trench accretionary prism forearc basin volcanic arc continental margin arc oceanic island arc “Ring of Fire” tectonic suture oceanic fracture zone