Download Homework Set 1

Geol 344: Earthquakes and Seismic Hazards
Spring 2006
Homework Set 2: Earthquake Depth Controls and Fault Slip
1. Use the USGS current earthquake information updates online (http:// earthquake.usgs.gov/
eqcenter/recenteqsww/Quakes/quakes_all.php) to find an example of a recent earthquake
that occurred along a subduction zone. (18 points total)
i)
ii)
iii)
iv)
v)
vi)
Which region did you select?
(2)
Navigate the webpage for this earthquake to find and then print out a map of the
region showing the historical seismicity from 1990 to the present.
(4)
Label the tectonic plates involved in this particular subduction zone.
(4)
Based on the earthquake depth distribution, which plate is subducting and towards
which direction? Provide your reasoning.
(3)
What type of subduction zone is this? (ocean-ocean or ocean-continent)
(2)
Use your answer to (v) to discuss whether the subducting plate you indicated in (iv)
is the plate that you would expect to be subducting. Provide all your reasoning. (3)
2. Answer the following sequence of questions about the seismogenic zone.
i)
ii)
iii)
iv)
Explain the meaning of the term seismogenic zone.
(2)
How are the depths of earthquakes generally controlled by the extent of this zone
(i.e., what is the typical depth range of the majority of earthquakes)?
(2)
Is there any preferred depth at which large magnitude earthquakes are likely to
nucleate, and why?
(2)
Explain why earthquakes in subduction zones can occur so much deeper than the
typical thickness of the seismogenic zone in either oceanic or continental
lithosphere.
(3)
3. Does every earthquake-producing fault extend all the way from the surface of the Earth down
to the base of the seismogenic zone? Explain your answer with a short paragraph that
describes the size and extent of faults in both the vertical and horizontal directions inside the
Earth’s crust. (or in other words, do faults go on forever in all directions, or do they have
some finite size? Think about the age of the fault and its effect on fault size.)
(5)
4.
i) What is meant by the term lithostatic stress and why is it pretty much the same thing
as a “pressure” inside the Earth?
(3)
ii) Can earthquakes happen if the only stress inside the crust is lithostatic stress?
Explain your reasoning.
(3)
iii) If rocks have a density of 2500 kg/m3, what is the lithostatic stress at a depth of
1 kilometer (1000 meters) inside the Earth?
(4)
5. If the maximum principal stress is oriented perpendicular to a vertical fault inside the crust,
would this fault be able to slip and produce an earthquake? Explain your reasoning in a few
sentences. (Hint: think about what causes sliding in any situation)
(4)
Geol 344: Earthquakes and Seismic Hazards
Spring 2006
6. Explain what the difference is between “stick-slip” sliding and “stable” sliding.
(4)
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