Ch 05 - Earhquake and Related Phenomena
Answers to Ch 05 Review Questions and Critical Thinking 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
9. An active fault is one that has ruptured within the last ten thousand
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
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
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
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