Page 442 - Global Tectonics

Review questions

1 a. Summarize the subdivisions of the Earth’s b. Describe two ways in which studies based on
silicate mantle and metallic core that have been the remanent magnetization of rocks have

deduced from seismologic studies. Indicate contributed to the verification of continental
briefly the type of seismologic study or drift and the formulation of plate tectonics.

observation that provides the evidence for each

6 a. Define the term transform fault and illustrate
layer that you mention. the six theoretical possibilities for active, right-
b. Suggest a plausible temperature distribution
lateral transform faults which do not terminate
within the Earth that is consistent with the in triple junctions. Indicate the way in which the
physical state and rheological properties of these
geometry of each type evolves with time and,
different layers. where possible, cite a recent or present day
2 a. Describe the way in which the seismic “fi rst example.
motion” at a number of seismologic observatories b. Explain the significance of transform faults

across the world can be used to obtain a focal when deducing the relative motion between
mechanism solution for an earthquake of adjacent lithospheric plates.
sufficiently large magnitude. 7 Explain the principles upon which the direction

b. Explain how, for near-surface earthquakes, such
and rate of relative motion between lithospheric
solutions can be related to a simple theory of plates are deduced for the different types of plate
faulting and hence to the principal stress
boundary developed at the Earth’s surface. Review
directions in the vicinity of the earthquake and briefly the types of argument used to convert

the sense of motion on the fracture.
these “relative” motions into “absolute” plate
3 Review critically the various lines of geophysical motions with respect to the Earth’s deep interior.
evidence suggesting that there is a layer of low To what extent do the resulting models for absolute
strength (the asthenosphere) in the upper mantle. plate motions differ?
How, if at all, does the depth of this layer vary

beneath different geological provinces? 8 a. Briefly outline the basic assumptions involved in
making a paleomagnetic study.
4 In the late 1960s four aspects of seismology provided
b. Explain qualitatively how the global paleo-
the basis for the formulation of the concept of plate magnetic dataset for rocks formed during the
tectonics:
past 200 Ma may be analysed to test:
a. more precise epicentral and focal depth i. the geocentric dipole model for the Earth’s
determinations;
magnetic fi eld;
b. the study of surface waves and free oscillations;
ii. the hotspot model for absolute plate
c. attenuation studies; and
motions; and
d. the determination of focal mechanism solutions.
iii. the suggestion that much of the Western
Explain briefly the nature and significance of each Cordillera of North America consists of

of these contributions. Show how a nearly complete “displaced” or “suspect” terranes.
statement of plate tectonics can be derived from
seismology alone. In each case state any assumptions and limitations
of the method.
5 a. Explain the underlying assumptions of the
paleomagnetic method for determining the 9 Explain the following plate tectonic concepts,
paleolatitude and orientation of a continental illustrating your answer with specifi c examples:
area. Outline the various stages involved in a. failed arms or rifts;
carrying out such a paleomagnetic study. b. triple junctions;
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