I
n this chapter we motivate the study of structural geology by introducing selected topics
that illustrate the extraordinary breadth of
interesting problems and important practical
applications of this discipline. For example, we
use the Imperial Valley earthquake of 1979 along
the San Andreas Fault zone to describe techniques for geological hazard analysis. In a second
example the lineaments visible in radar images
of Venus provide the data for investigating tectonic processes on a planet other than our own.
This is followed by an investigation of normal
faulting in a hydrocarbon reservoir under the
North Sea, off the coast of Norway, to introduce
an application to petroleum exploration and
production. Then we describe the pattern of
small faults, veins, and solution surfaces from
an exposure in southern France, an example that
demonstrates the practice of structural geology
at the human scale. The concept of “anticracks”
that emerged from this academic investigation
is now being used to help explain the origin of
huge earthquakes a hundred kilometers below
Earth’s surface. Finally, we describe a mechanism for mountain building that was discovered
in the Henry Mountains of southern Utah in the
late nineteenth century by one of the pioneers of
structural geology, G. K. Gilbert.
The frontispiece for this chapter is a photograph of Mt. Hillers in the southern Henry
Mountains. Like all the photographs that appear
as grayscale images in this book, a color image
of this photograph is available at the textbook
website along with images of related exposures
and scenes. These are presented as monitor
resolution images for quick viewing with a web
browser or for LCD projection in the classroom for
teaching purposes.
1.1 Earthquake hazards in
southern California
Academic researchers have learned that society
may not be content to continue funding the
arcane studies of ancient rocks that have been the
mainstay of the National Science Foundation’s
Tectonics Program in the past. Darrel Cowan, then
President of the Geological Society of America’s
Structural Geology and Tectonic Division, concluded:
We are at the end of the era when an unquestioning
public belief in the benefits of basic scientific research
almost automatically led to increased budgets at the
NSF (National Science Foundation) Program level.
Already, NSF management and the Congress want to
hear arguments about how research, and especially
new programs, will address important social issues:
environmental changes and hazards, exploitation,
waste, and recycling of natural resources, and the like
(Cowan, 1992).
Thus, whether a career in the Earth sciences takes
one to industry or to academia or to a government
laboratory, the structural geologist should know
how to address problems of social importance. To
this end, we integrate aspects of active tectonics,
engineering geology, and petroleum geology into
this book to show how structural geology can
contribute to solving problems in these areas.
Most inhabitants of southern California are
familiar with earthquakes and the geological
hazard associated with living in an active tectonic
province, although the recurrence time of major
events is great enough to instill a sense of complacency in many citizens. On the other hand,
Earth scientists and government officials are
acutely aware that destructive earthquakes could
occur at any moment. Teams of scientists and
engineers supported by federal and local governments are monitoring the continuing activity of
the faults in this area and have tools in place to
capture data from the next significant event (Yeats
et al., 1997).
What are the data that these scientists and
engineers are hoping to capture? Perhaps the
most fundamental aspect of faulting is the fact
that the rock and soil on either side of the fault
slip past one another. There is relative motion of
these two masses more or less parallel to the fault
surface. For example, Fig. 1.1 is a photograph
taken across the trace of the Imperial Fault in the
Imperial Valley of southern California shortly
after a magnitude 6.5 earthquake struck on
October 15, 1979. The vertical surface just behind
the observer’s feet is one surface of the fault
exposed at the time of the earthquake. Relative to
the ground on which the observer is standing, slip
2
MOTIVATIONS AND OPPORTUNITIES
n this chapter we motivate the study of structural geology by introducing selected topics
that illustrate the extraordinary breadth of
interesting problems and important practical
applications of this discipline. For example, we
use the Imperial Valley earthquake of 1979 along
the San Andreas Fault zone to describe techniques for geological hazard analysis. In a second
example the lineaments visible in radar images
of Venus provide the data for investigating tectonic processes on a planet other than our own.
This is followed by an investigation of normal
faulting in a hydrocarbon reservoir under the
North Sea, off the coast of Norway, to introduce
an application to petroleum exploration and
production. Then we describe the pattern of
small faults, veins, and solution surfaces from
an exposure in southern France, an example that
demonstrates the practice of structural geology
at the human scale. The concept of “anticracks”
that emerged from this academic investigation
is now being used to help explain the origin of
huge earthquakes a hundred kilometers below
Earth’s surface. Finally, we describe a mechanism for mountain building that was discovered
in the Henry Mountains of southern Utah in the
late nineteenth century by one of the pioneers of
structural geology, G. K. Gilbert.
The frontispiece for this chapter is a photograph of Mt. Hillers in the southern Henry
Mountains. Like all the photographs that appear
as grayscale images in this book, a color image
of this photograph is available at the textbook
website along with images of related exposures
and scenes. These are presented as monitor
resolution images for quick viewing with a web
browser or for LCD projection in the classroom for
teaching purposes.
1.1 Earthquake hazards in
southern California
Academic researchers have learned that society
may not be content to continue funding the
arcane studies of ancient rocks that have been the
mainstay of the National Science Foundation’s
Tectonics Program in the past. Darrel Cowan, then
President of the Geological Society of America’s
Structural Geology and Tectonic Division, concluded:
We are at the end of the era when an unquestioning
public belief in the benefits of basic scientific research
almost automatically led to increased budgets at the
NSF (National Science Foundation) Program level.
Already, NSF management and the Congress want to
hear arguments about how research, and especially
new programs, will address important social issues:
environmental changes and hazards, exploitation,
waste, and recycling of natural resources, and the like
(Cowan, 1992).
Thus, whether a career in the Earth sciences takes
one to industry or to academia or to a government
laboratory, the structural geologist should know
how to address problems of social importance. To
this end, we integrate aspects of active tectonics,
engineering geology, and petroleum geology into
this book to show how structural geology can
contribute to solving problems in these areas.
Most inhabitants of southern California are
familiar with earthquakes and the geological
hazard associated with living in an active tectonic
province, although the recurrence time of major
events is great enough to instill a sense of complacency in many citizens. On the other hand,
Earth scientists and government officials are
acutely aware that destructive earthquakes could
occur at any moment. Teams of scientists and
engineers supported by federal and local governments are monitoring the continuing activity of
the faults in this area and have tools in place to
capture data from the next significant event (Yeats
et al., 1997).
What are the data that these scientists and
engineers are hoping to capture? Perhaps the
most fundamental aspect of faulting is the fact
that the rock and soil on either side of the fault
slip past one another. There is relative motion of
these two masses more or less parallel to the fault
surface. For example, Fig. 1.1 is a photograph
taken across the trace of the Imperial Fault in the
Imperial Valley of southern California shortly
after a magnitude 6.5 earthquake struck on
October 15, 1979. The vertical surface just behind
the observer’s feet is one surface of the fault
exposed at the time of the earthquake. Relative to
the ground on which the observer is standing, slip
2
MOTIVATIONS AND OPPORTUNITIES