Geology 001                                                                                        West Valley College

Physical Geology                                                                                  R. Lopez


Study Questions: Earthquakes and Faults

1)      Define both stress and strain.  What is strain energy?

2)      About how much faster is a P-wave than an S-wave?  About how much slower are the surface waves from the S-wave?

3)      Strain is the result of what kind of changes in a rock?

4)      What are the three types of stresses? What tectonic boundary is related to each?  Sketch all three showing arrows of deforming stress.

5)      What are the links between deformation, energy, and earthquakes?

6)      How are earthquakes and faults related?

7)      Describe the elastic rebound theory.

8)      Describe and sketch the relationship between the focus, epicenter, and surface rupture for a dipping fault plane. 

9)      Where do deep focus earthquakes occur, what is the maximum depth to their focus, and what controls this limit?  (Why is there a Benioff Zone?)

10)  What are typical focal depths of California earthquakes?

11)  What is the relationship between rock types (hard vs. soft and consolidated vs. unconsolidated) and ground shaking.

12)  How do seismographs work?

13)  Define seismograph, seismogram, epicenter, focus, p-wave, s-wave, Love wave, Rayleigh wave, surface waves, body waves, amplitude, logarithm, s-p interval, unconsolidated, magnitude, and intensity.

14)  Sketch a simple seismograph depiction horizontal movement.

15)  How are active faults officially defined? What is the Alquist-Priolo Law?

16)  What are the differences among P, S, and surface waves? 

17)  What is the evidence that the outer core is liquid? 

18)  Sketch a simple seismogram tracing showing the P, S and surface waves.

19)  Discuss how the epicenter of an earthquake can be located?  Be able to do this on an exam.  Know how to calculate p-wave and s-wave arrival times off of a seismogram.  Know how to calculate distance to epicenter using the (s-p) vs distance curves.

20)  What specifically controls the Richter magnitude?  Be able to compare the amplitudes of seismic waves yielding different Richter magnitudes (e.g., compare amplitudes of magnitude 4 and 6 quakes).

21)  What is the principal problem with the Richter magnitude?  (“The Richter magnitude does not directly measure the overall mechanical power of the seismic source, just as the strongest wind gust is not a reliable measure of the overall force of a wind storm.” Bolt, 1993, p. 59).

22)  What is MW, why is it “better” than the Richter magnitude, and what three factors are considered in its calculation?

23)  What is MO?  Calculate the Mw of an earthquake with 5.5 meters of slip over a 300 km x 2 km area with rock having an elastic modulus of 8.2 x 1010 N/m2

24)  How does “earthquake intensity” differ from magnitude, how is it measured, and what factors influence it?

25)  What is the San Andreas Fault System?  On a map, be able to identify the San Francisco Bay Area faults discussed in lecture.

26)  What is creep and how does if differ from a long-term slip rate?

27)  Name two nearby faults that creep.

28)  What is a seismic gap, and what is the seismic gap theory?

29)  Which is the most dangerous fault in the San Francisco Bay Area?

30)  Why is the fault referred to in question above considered to be the most dangerous?

31)  Using seismic gap theory, where will the next earthquake occur along the San Andreas Fault in the San Francisco Bay area?

32)  Compare and contrast the amount of slip (displacement) that occurred during the 1906 S.F. quake and the 1989 Loma Prieta quake.

33)  What was the time of shaking for each of these quakes mentioned above?

34)  A seismograph records the p-wave arrival time at 1:00pm and 30 seconds.  The s-waves arrives at 1:02pm and 15 seconds.  What is the (s-p) interval?  What time did the earthquake rupture?