Ch 05 - Earhquake and Related Phenomena Answers to Ch 05 Review Questions and Critical Thinking Questions Review Questions 1. The focus is the point of rupture on the fault plane at depth, while the epicenter is the point on the ground surface directly above the focus. 2. The Richter magnitude is determined through measurement of the amplitude of waves on seismograms. 3. Moment magnitude is a measure of the energy released by the earthquake, and is based on the area of rupture along a fault plane, the amount of slip, and the rigidity of the rocks. 4. The Modified Mercalli Scale is based on the perception of people and the response of structures to earthquake shaking. 5. Magnitude is the amount of energy released, determined either by seismogram interpretation (Richter) or faulting characteristics at the source (Moment), while intensity is the amount of shaking at a location, determined by observations (Mercalli) or interpretation of seismograms (instrumental). 6. A fault is a fracture along which rocks have moved. 7. The major types of faults are strike slip (left lateral and right lateral) and dip slip (normal, reverse, and thrust). 8. In an anticline, the fold is upward, while, in a syncline, the fold is downward. 9. An active fault is one that has ruptured within the last ten thousand years. 10. Tectonic creep is the movement, usually relatively constant, of two fault blocks along a fault without felt earthquakes. 11. The main types of seismic waves are body waves (P and S) and surface waves. 12. P-waves are compressional waves (pushing and pulling rock particles as they move), while S-waves are shear waves (up and down or side-to-side motion perpendicular to the direction of wave travel). These properties help determine their effects. P-waves generate compressional sound waves, allowing the earthquake to be heard before the shaking begins, and P-waves cause small amounts of shaking while S-waves, with their transverse motion, generate greater shaking. 13. Material amplification is the increase of wave amplitude by unconsolidated sediments. 14. The earthquake cycle is the cycle of elastic strain buildup and release. Following a major earthquake, the first stage is a quiescent period, the second involves long-term elastic strain buildup and generates increased seismicity, the third involves foreshocks, and the fourth is the major earthquake event, which releases the accumulated elastic strain. 15. Human activity has caused earthquakes by 1) construction of dams and reservoirs, 2) injection of liquid wastes, and 3) creation of nuclear explosions. 16. Some of the major effects of earthquakes include shaking, liquefaction, landslides, fire, disease, tsunami, and regional change in land elevation. 17. Precursor phenomena include preseismic deformation, emission of radon gas, seismic gaps, and anomalous animal behavior. 18. The major goals of earthquake hazard reduction programs are to develop an understanding of the earthquake source, to determine the earthquake potential, to predict the effects of earthquakes, and to apply research results to help people and communities better plan for earthquakes. 19. The main adjustments people make are community-level adjustments (building codes, education) and personal adjustments (home safety checks, and plans for responses to an earthquake). Critical Thinking Questions 1. The first step in this task should involve basic discussions about the nature of earthquake hazards and about the danger of unreinforced buildings. Subsequent steps should include development of community- and personal-level plans for response to an earthquake, and a long-term, methodical program for reinforcement of structures. 2. A response to this question should include a discussion of both the scientific uncertainties of earthquake prediction and of personal attitudes and philosophies regarding the expectations of such a warning system and how society might and should respond to the presence or absence of a warning system.