review some useful mathematics in an Appendix, to which we
refer. Other mathematical concepts, notably topics in Fourier
analysis, are used as needed and then presented in more depth
when appropriate.
Our goal is to introduce some concepts about seismology
and its application to such studies of earth structure and earthquakes. Doing this requires developing basic ideas about wave
propagation in a continuous solid medium, so the material of
greatest interest to geologically oriented readers is somewhat
postponed. Readers are urged to enjoy rather than endure the
introductory material on elasticity and wave propagation. They
risk only discovering the appeal of these topics and finding
themselves taking subsequent advanced courses.
Part of the delights of the earth sciences is that they are less
structured than some other sciences. There is no single set of
topics covered in specific courses, which instead reflect the
instructor’s and students’ interests. Certainly this is the case
here. The topics we have chosen contain about a year’s worth
of class material, which we ourselves divide into several
courses. Many students, of course, take only one. We have
experimented with different groupings, all of which seemed to
work well. We usually do not cover the Appendix in lectures,
but assign its problems to identify areas for study or review.
We have found that the homework problems are helpful
for understanding the topics. Given the nature of the modern
earth sciences, many problems are designed to be done on computers. In our teaching, we expect that most will be done by
writing programs, and hence require programming, beginning
with simple problems in the Appendix and building to more
complex ones in the chapters. A secondary motive is to ensure
that students learn the skills of scientific programming, which
are often not stressed in computer classes. Some of the problems can be done using spreadsheets, and most can be done
with specialized mathematical software.
Some matters of style are worth mentioning. We illustrate
interconnections between topics by referring both forward and
backward to other sections. Figures are labeled with hyphens
(e.g. 5.6-2), and equations with periods (e.g. 5.3.2). Footnotes
generally cover side observations which we note in class but are
not essential. We use both SI units (those based on the meter,
kilogram, and second) and cgs units (those based on the
centimeter, gram, and second) because both are common in the
literature, although SI units are slowly superseding cgs. We also
use other units when customary: seismic velocities are given
in km/s and plate motions are given in the more intuitive
mm/yr (e.g., 48 mm /yr rather than 1.5 × 10 −9 m/s), following
Emerson’s dictum that “a foolish consistency is the hobgoblin
of little minds.”
We have enjoyed writing this book. It is a pleasure to try to
summarize this diverse and fascinating discipline. We hope
readers have as much fun as we did, and that our discussions
prompt them to raise interesting and provocative questions as
well as learn the material. We also hope that some readers are
motivated to continue study of and research on these topics.
Much remains to be learned about the earth and earthquake
processes, and the opportunities for contributions are great
for those with the energy and imagination to go beyond our
current knowledge and ideas. Three hundred years after Isaac
Newton’s work in mechanics and optics laid what would
become seismology’s foundations, it is worth recalling his
words: “I seem to have been only like a boy playing on the
seashore, and diverting myself in now and then finding a
smoother pebble or a prettier shell than ordinary, whilst the
great ocean of truth lay all still undiscovered before me.”
x Preface
refer. Other mathematical concepts, notably topics in Fourier
analysis, are used as needed and then presented in more depth
when appropriate.
Our goal is to introduce some concepts about seismology
and its application to such studies of earth structure and earthquakes. Doing this requires developing basic ideas about wave
propagation in a continuous solid medium, so the material of
greatest interest to geologically oriented readers is somewhat
postponed. Readers are urged to enjoy rather than endure the
introductory material on elasticity and wave propagation. They
risk only discovering the appeal of these topics and finding
themselves taking subsequent advanced courses.
Part of the delights of the earth sciences is that they are less
structured than some other sciences. There is no single set of
topics covered in specific courses, which instead reflect the
instructor’s and students’ interests. Certainly this is the case
here. The topics we have chosen contain about a year’s worth
of class material, which we ourselves divide into several
courses. Many students, of course, take only one. We have
experimented with different groupings, all of which seemed to
work well. We usually do not cover the Appendix in lectures,
but assign its problems to identify areas for study or review.
We have found that the homework problems are helpful
for understanding the topics. Given the nature of the modern
earth sciences, many problems are designed to be done on computers. In our teaching, we expect that most will be done by
writing programs, and hence require programming, beginning
with simple problems in the Appendix and building to more
complex ones in the chapters. A secondary motive is to ensure
that students learn the skills of scientific programming, which
are often not stressed in computer classes. Some of the problems can be done using spreadsheets, and most can be done
with specialized mathematical software.
Some matters of style are worth mentioning. We illustrate
interconnections between topics by referring both forward and
backward to other sections. Figures are labeled with hyphens
(e.g. 5.6-2), and equations with periods (e.g. 5.3.2). Footnotes
generally cover side observations which we note in class but are
not essential. We use both SI units (those based on the meter,
kilogram, and second) and cgs units (those based on the
centimeter, gram, and second) because both are common in the
literature, although SI units are slowly superseding cgs. We also
use other units when customary: seismic velocities are given
in km/s and plate motions are given in the more intuitive
mm/yr (e.g., 48 mm /yr rather than 1.5 × 10 −9 m/s), following
Emerson’s dictum that “a foolish consistency is the hobgoblin
of little minds.”
We have enjoyed writing this book. It is a pleasure to try to
summarize this diverse and fascinating discipline. We hope
readers have as much fun as we did, and that our discussions
prompt them to raise interesting and provocative questions as
well as learn the material. We also hope that some readers are
motivated to continue study of and research on these topics.
Much remains to be learned about the earth and earthquake
processes, and the opportunities for contributions are great
for those with the energy and imagination to go beyond our
current knowledge and ideas. Three hundred years after Isaac
Newton’s work in mechanics and optics laid what would
become seismology’s foundations, it is worth recalling his
words: “I seem to have been only like a boy playing on the
seashore, and diverting myself in now and then finding a
smoother pebble or a prettier shell than ordinary, whilst the
great ocean of truth lay all still undiscovered before me.”
x Preface