Preface
1 Because subfields in the earth sciences overlap, the divisions between them are
not sharp, and a given topic draws on several. As John Muir, an early member of the
Seismological Society of America better known for founding the Sierra Club, pointed
out, “when we look at anything in isolation we realize it is hitched to the rest of the
universe.”
Science is only worth doing if it is interesting and fun. Hence
the goal of a textbook is to interest students in a subject, convince them it is worth the effort required to learn about it, and
help them do so. We have tried here to do all three.
For seismology, these should be easy. It is hard to imagine
topics more interesting than the structure and evolution of a
planet, as manifested by phenomena as dramatic as earthquakes. Our goal is to address them via an introduction to
seismology, which is one of the cornerstones of the modern
earth sciences. Seismology has been defined as the study of
earthquakes and associated phenomena, or the study of elastic
waves propagating in the earth. By integrating techniques and
data from physics, mathematics, and geology, seismology has
produced a remarkably sharp picture of the earth’s interior
that is a primary datum for studying the formation and evolution of terrestrial planets. Seismologists have also learned much
about the nature of earthquakes and the tectonic processes
responsible for them. These studies are not of purely academic
interest; seismology is the major tool for earthquake hazard
assessment, hydrocarbon exploration, and the peacekeeping
role of nuclear test monitoring.
We thus believe that seismology should be part of the education of every solid earth scientist, rather than a specialized
course for those whose primary interest is seismology or other
branches of geophysics. The subject has much to offer mineralogists or petrologists studying the composition of the earth’s
interior, students of tectonics interested in processes of the
lithosphere, geologists interested in the nature and evolution
of the crust, engineers concerned with seismic hazards, and
planetologists interested in the evolution of the terrestrial planets. As the earth sciences become increasingly more integrated
and interdisciplinary, the advantages of understanding seismology will continue to grow.
Many students have been deterred from the subject because
it requires confronting, often for the first time, both the physics
of a continuous medium and wave propagation. We view these
concerns as manageable. In fact, we believe that seismology is
a good way to introduce these topics, because it applies what
might otherwise seem abstract ideas. Seismic waves illustrate
effects like reflection, refraction, diffraction, and dispersion
by using them to study the earth. Earthquakes demonstrate
concepts like rigid tectonic plates, stress and strain, and viscous
mantle flow. Thus seismology is a natural way to discuss fundamental processes.
Our goal is to introduce key concepts and their application in
present research. This twofold goal places several limitations
on the text. First, time and space restrictions require a trade-off
between the range of topics and the level of presentation. The
resulting choices are, of necessity, subjective. Second, we end
discussions when material, however fascinating, seems more
appropriate for advanced classes or courses in a related field. 1
Third, these limitations preclude an account of the historical
development of the subject, or a systematic assignment of
credit for ideas and results. Fourth, in introducing topics of current research, we try to give our sense of issues while recognizing that others’ views may differ. The danger in presenting the
“current state of knowledge” in a text is that the field changes
so rapidly that accounts can soon be out of date. We thus try to
focus not on “what we know,” but on “how we seek to find
out,” and highlight current findings in the context of studying
interesting questions.
Given these limitations, suggestions for further reading are
provided. When possible, the readings are texts or reviews
rather than specialized research papers. In many cases, the
sources of the figures used to illustrate a concept provide
additional information. We also give some references to sites
on the World Wide Web, recognizing the trade-off between the
wealth of information there and the fact that the Web is volatile
and sites can change locations or vanish.
The material is designed for advanced undergraduates and
first-year graduate students. Readers are assumed to be familiar with ordinary differential equations and introductory
physics. Further background, including basic earth science
courses, is helpful but not essential. Material beyond this level
is derived as needed. Thus, we seek a balance between presenting the mathematics like magic pulled from a hat and deriving
so much so that the thematic flow is disrupted. Hence we
1 Because subfields in the earth sciences overlap, the divisions between them are
not sharp, and a given topic draws on several. As John Muir, an early member of the
Seismological Society of America better known for founding the Sierra Club, pointed
out, “when we look at anything in isolation we realize it is hitched to the rest of the
universe.”
Science is only worth doing if it is interesting and fun. Hence
the goal of a textbook is to interest students in a subject, convince them it is worth the effort required to learn about it, and
help them do so. We have tried here to do all three.
For seismology, these should be easy. It is hard to imagine
topics more interesting than the structure and evolution of a
planet, as manifested by phenomena as dramatic as earthquakes. Our goal is to address them via an introduction to
seismology, which is one of the cornerstones of the modern
earth sciences. Seismology has been defined as the study of
earthquakes and associated phenomena, or the study of elastic
waves propagating in the earth. By integrating techniques and
data from physics, mathematics, and geology, seismology has
produced a remarkably sharp picture of the earth’s interior
that is a primary datum for studying the formation and evolution of terrestrial planets. Seismologists have also learned much
about the nature of earthquakes and the tectonic processes
responsible for them. These studies are not of purely academic
interest; seismology is the major tool for earthquake hazard
assessment, hydrocarbon exploration, and the peacekeeping
role of nuclear test monitoring.
We thus believe that seismology should be part of the education of every solid earth scientist, rather than a specialized
course for those whose primary interest is seismology or other
branches of geophysics. The subject has much to offer mineralogists or petrologists studying the composition of the earth’s
interior, students of tectonics interested in processes of the
lithosphere, geologists interested in the nature and evolution
of the crust, engineers concerned with seismic hazards, and
planetologists interested in the evolution of the terrestrial planets. As the earth sciences become increasingly more integrated
and interdisciplinary, the advantages of understanding seismology will continue to grow.
Many students have been deterred from the subject because
it requires confronting, often for the first time, both the physics
of a continuous medium and wave propagation. We view these
concerns as manageable. In fact, we believe that seismology is
a good way to introduce these topics, because it applies what
might otherwise seem abstract ideas. Seismic waves illustrate
effects like reflection, refraction, diffraction, and dispersion
by using them to study the earth. Earthquakes demonstrate
concepts like rigid tectonic plates, stress and strain, and viscous
mantle flow. Thus seismology is a natural way to discuss fundamental processes.
Our goal is to introduce key concepts and their application in
present research. This twofold goal places several limitations
on the text. First, time and space restrictions require a trade-off
between the range of topics and the level of presentation. The
resulting choices are, of necessity, subjective. Second, we end
discussions when material, however fascinating, seems more
appropriate for advanced classes or courses in a related field. 1
Third, these limitations preclude an account of the historical
development of the subject, or a systematic assignment of
credit for ideas and results. Fourth, in introducing topics of current research, we try to give our sense of issues while recognizing that others’ views may differ. The danger in presenting the
“current state of knowledge” in a text is that the field changes
so rapidly that accounts can soon be out of date. We thus try to
focus not on “what we know,” but on “how we seek to find
out,” and highlight current findings in the context of studying
interesting questions.
Given these limitations, suggestions for further reading are
provided. When possible, the readings are texts or reviews
rather than specialized research papers. In many cases, the
sources of the figures used to illustrate a concept provide
additional information. We also give some references to sites
on the World Wide Web, recognizing the trade-off between the
wealth of information there and the fact that the Web is volatile
and sites can change locations or vanish.
The material is designed for advanced undergraduates and
first-year graduate students. Readers are assumed to be familiar with ordinary differential equations and introductory
physics. Further background, including basic earth science
courses, is helpful but not essential. Material beyond this level
is derived as needed. Thus, we seek a balance between presenting the mathematics like magic pulled from a hat and deriving
so much so that the thematic flow is disrupted. Hence we