OPINION
IS THE STUDY OF EARTHQUAKES A BASIC
SCIENCE?
like Japan have been disheartening. Previously proposed
schemes for short-term earthquake prediction have not
proven to be successful, and despite the substantial increase
in monitoring capability, no unambiguous precursory sigI
believe the answer to this question is yes, although I'm
not sure how many scientists would agree. For example,
nals have been identified that are diagnostic in the sense
I suspect that most of my M I T colleagues in physics,
required for useful short-term prediction.
chemistry, and biology would characterize earthquake studThe collapse of earthquake prediction as a unifying
ies as a strictly applied science. They would quickly concede,
theme and driving force behind earthquake science has
of course, that the study of earthquakes has been stunningly
caused a deep crisis. One reaction has been to declare that
successful as an applied science. Many
the predictability issue is essentially
of them appreciate the remarkable
solved: while some long-term aspects
The current situation presents
progress in mapping active faults and
of earthquake activity can be forecast
characterizing the paleoseismic history
probabilistically, earthquakes in genus with an unusual opportunity
of regions like Southern California and
eral
are just not predictable in the sense
for scientific leadership. In
the Pacific Northwest, and some are
of the term understood and desired by
fact, the sheer intransigence
the general public; i.e., close bounds
aware of the improved capability for
of the problems we face in the
the rapid collection, analysis, and dison the locations, times, and sizes of
study of earthquakes leaves us
semination of seismological data folindividual large earthquakes. This conno choice but to extend the
lowing a damaging earthquake. On the
tention is based on the notion that
other hand, the older among them
active
fault systems are chaotic; that
limits of science.
probably know that the overall
knowing the state of the system even
achievements in applied earthquake
very precisely at one instant, say at the
science have not yet matched the high expectations of three
time an earthquake is nucleating, is not sufficient to predict
decades ago, when it appeared that short-term earthquake
its behavior just a short time later--e.g., how big the nucleprediction might be right around the corner.
ating earthquake will get before the rupture stops, kYc'hilethis
Following the damage caused by the great I964 Alaskan
thinking may apply to some classes of earthquakes, such as
earthquake, a select committee chaired by Frank Press issued
intermediate-sized events in California, it would be premaa report entitled Earthquake Prediction: A Proposalfor a Ten
ture to generalize the behavior to all large earthquakes. A
Year Program of Research (White House Office of Science and
more prudent statement is that we still don't know how to
Technology, 1965). The optimism reflected in the title of
answer the question, "Which types of earthquakes, if any, are
this report was heightened in the early 1970s by the apparent
short-term predictable?" Having said that, we can hardly
successes of some empirical prediction schemes and the plaumaintain an optimistic attitude towards the feasibility of
sibility of the physical-process models (e.g., dilatancy diffudeterministic prediction, at least in the short term.
sion) upon which they were based. By 1976 a distinguished
What, then, are the issues that should drive earthquake
panel of earthquake scientists convened by the National
science? There is, of course, a menu of interesting problems
Research Council's Committee on Seismology was willing
related to the practical aspects of hazards mitigation that we
to state:
can and should be solving, such as improving the technologies for real-time seismology and rapid response, predicting
"The Panel unanimously believes that reliable earthquake
the strong ground motions for major events, and using modprediction is an achievable goal. We will probably predict
ern geological and geodetic techniques for refining seismic
an earthquake of at least magnitude 5 in California
hazard maps. These problems are scientifically challenging in
within the next five years in a scientifically sound way
their own right, and their importance to our globalized sociand with a sufficiendy small space and time uncertainty
ety
is beyond dispute. The practical study of earthquakes is a
to allow public acceptance and effective response."
healthy and vigorous applied science that continues to
deserve strong support from the federal funding agencies.
Although more than 100 earthquakes have occurred in CalBut the applied-science menu is too meager a diet for
ifornia with magnitudes greater than 5.0 in the intervening
sustaining earthquake research as a whole. For example, the
twenty years, this promise remains unfulfilled. In fact, the
best and brightest students are not likely to be attracted to a
observations in California and other well-instrumented areas
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Volume 68, Number 2
March/April 1997
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strictly applied science that is primarily a consulting service
for engineers (which is, unfortunately, the current situation in
the environmental earth sciences). Our prospective young
researchers would find it pretty glum if they were looking forward to scientific careers dominated by the task of microzonation. Moreover, the public would quickly lose interest in such
a pedestrian enterprise. To remain healthy, earthquake science
must be draw from the essential issues of basic science.
A precise definition of basic science is elusive, but three
of its functions are clear. The first is to provide the knowledge base needed to improve the methodologies of applied
science, in this case the practical aspects of earthquake hazard mitigation, which is itself a broad mandate for doing all
kinds of interesting research. Take, for example, the difficult
problem of seismic wave scattering in heterogeneous, anisotropic media like the Earth's crust and upper mantle, which
happens to be a subject of my own recent research; I can
argue that this work, although quite removed from the central issues of earthquake hazards, might eventually improve
algorithms for imaging rupture processes or models for predicting strong ground motions. Such a long-term, knowledge-based strategy was adopted twenty years ago in setting
up the National Earthquake Hazard Reduction Program,
and it has proven to be enormously successful in delivering
practical benefits. Given the recent external criticisms of
NEHRP, the earthquake-research community should assert
this point more aggressively. A powerful case can and should
be made for a fundamental approach to the earthquake hazard problem, especially in the arena of assessing hazard
potential.
The second function of basic science is to improve fundamental understanding in a way that contributes to other
areas of applied and basic science. For example, the laboratory study of earthquake fracture mechanics and fault friction has led to dynamical models and constitutive relations
that are being applied in materials engineering. Today, the
theoretical investigation of episodic deformation is addressing the fundamental problem of strain localization in the
lithospheres of the Earth and other terrestrial planets. And
we should not forget the profound role that earthquake science played in the plate tectonic revolution, which counts as
one of the major accomplishments of twentieth-century science. Earthquake studies will continue in this role as a basic
component of the geosciences.
It is more difficult to maintain that earthquake science is
somehow fundamental to science in general, but let me try
to make this case. The key to this argument is the recognition that the spectrum of basic science ranges between two
extremes. One side is the goal of reductionism, that grand
march begun 400 years ago towards discovering the fundamental laws of the universe. The reductionist program seeks
to take apart the complexity of the world and reduce it to
simple statements about fundamental forces and, ultimately,
to intrinsic symmetries. This grand march continues,
although to many, myself included, it appears to be receding
into the shadows of the unobservable.
At the other end of the scientific spectrum lies the goal
of understanding the very complex systems of the natural
world, which can be grouped according to their proximity
and their scale; they range from the biosystems of individual
organisms and the ecosystems of groups of organisms, to the
geosystems of the Earth and the other planets, outward to
the astrosystems of the stars and the galaxies beyond. The
scientific approach to the study of natural systems that is
most in line with the reductionist agenda is the so-called
"constructionist program," which can be summarized as follows: from the fundamental laws that characterize the basic
processes among the elements of the system, we seek to
describe quantitatively the essential aspects of the system's
behavior. One of the great disappointments of reductionism
has been the conceptual failure of this approach. In 1972,
Philip Anderson wrote an article in Science entitled "More Is
Different" in which he asserted:
"The reductionist hypothesis does not by any means
imply a 'constructionist' one: the ability to reduce everything to simple fundamental laws does not imply the
ability to start from those laws and reconstruct the universe. In fact, the more the elementary-particle physicists
tell us about the nature of fundamental laws, the less relevance they seem to have to the very real problems of the
rest of science, much less to those of society. The constructionist hypothesis breaks down when confronted
with the twin difficulties of scale and complexity."
This failure is rooted in what the philosophers of science call
ontological decoupling. Silvan Schweber, a historian of science writing the November, 1993 issue of Physics Today,
described the situation as follows:
"The reductionist approach that has been the hallmark of
theoretical physics in the 20th century is being superseded by the investigation of emergent phenomena...
These conceptual developments...have revealed a hierarchical structure of the physical world. Each layer of the
hierarchy is successfully represented while remaining
largely decoupled from other layers."
In other words, each level of science has its own "fundamental," though usually approximate, equations. But knowing
these equations is not enough, because it is not the equations
but their solutions that provide mathematical descriptions of
physical phenomena. "Emergence" refers to the properties of
the solutions that are not readily apparent from the equations themselves, a prime example being deterministic chaos.
Geosystems, ranging from the global systems of climate,
mantle convection, and the geodynamo to more localized
systems like petroleum reservoirs, hurricanes, and active
fault systems, provide some of the best examples of emergent
phenomena. The first systematic treatment of chaos in a dissipative system was Ed Lorenz's 1963 paper, "Deterministic
non-periodic flow," which investigated simple models of
atmospheric convection. Systems concepts like universality
and self-organized criticality, which have been applied in a
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prominent way by physicists and geophysicists to earthquake
phenomena, have proliferated into a vast array ofbuzzwords,
heralding the synthesis of a new science of complex systems.
Now, when a physicist talks about a complex system,
she's usually referring to a very simple system that exhibits
complex behavior. Geosystems are truly complex in that they
lie way beyond what we might call the "constructionist frontier," and they therefore present special, unsolved problems
of observation, analysis, and inference. Earthquake science
should be able to lead the intellectual development at this
end of the scientific spectrum. Look at the competition.
Biology certainly has a legitimate claim to complexity, but
most of biology is now preoccupied with a reductionist-constructionist program that sees organisms as implementations
of the genetic code. Indeed, modern molecular biology is the
science where the constructionist agenda has been the most
successful, because the master molecule, DNA, provides an
essentially deterministic template for the most fundamental
biological processes. The nonconstructionists--e.g., ecologists and evolutionary biologists--have been marginalized,
their efforts judged largely on how much they employ modern genetic methodologies. Or take the science of astronomy.
Astrosystems are manifestly complex, but the problems that
astrophysicists consider to be the most important are those
of cosmology; i.e., the ones most directly connected to fundamental physics. Many astrophysicists are thus co-opted by
the old reductionist program.
The current situation presents us with an unusual
opportunity for scientific leadership. In fact, the sheer intransigence of the problems we face in the study of earthquakes
leaves us no choice but to extend the limits of science. Faults
systems are among the most vexing geosystems to model
because the essential dynamics of fault interactions involve
such a wide range of spatial and temporal scales. Furthermore, they are largely opaque. In comparison, the climate
system, though immensely complicated, is fairly transparent
and accessible to observation. How do you progress towards
understanding a geosystem for which the data are so incomplete and inaccurate and where most of the system is hidden
from view? This ignorance forces us to develop new technologies for remote sensing, new methods for inversion and data
assimilation, and new concepts in the theory of inference. It
pushes us towards the scientific frontier.
Crucial to this endeavor is the question of predictability,
because the continuing prediction of a geosystem's behavior
is the truest measure of how well it is understood. I'm not
here referring narrowly to earthquake prediction but more
generally to the ability to simulate a priori the full range of
behaviors of active fault systems and to know which aspects
of these behaviors are most deterministic. The methods for
investigating geosystem predictability are very primitive, and
there is ample room for seminal breakthroughs that could
have wide application to other natural systems. We must
advance this line of inquiry more quickly.
This brings me to the third function of basic science,
which is to enlighten humanity about its place in the world.
It is no accident that astronomy and evolutionary biology are
the two most popular sciences; they are valued by the general
public precisely because they provide a physical and temporal context for our civilization. Our job as earthquake scientists is certainly tougher in this respect than that of the
astronomer or dinosaur specialist, since large earthquakes are
usually an unexpected form of very bad news. Nevertheless,
it is our responsibility to provide a rational context for living
on a restless Earth governed by natural forces that can never
be totally understood and are certainly beyond our control.
To hear the need for this perspective, listen to Bill McKibben
complain in his book The End of Nature:
"about the sadness of a world where there is no escaping
man. Although for decades civilization has pillaged and
polluted the Earth, in the past those attacks were relatively localized; now, with the global changes caused by
greenhouse gases and ozone erosion, man has altered the
most elemental process of life everywhere, and the outdoors, nature itself, has been turned into the equivalent
of an enormous heated room. The basic forces of nature,
once beyond man's reach, will forever more be subjects of
man's domination."
McKibben's vision reminds me of Isaac Asimov's description
of Trantor, the Earth-like planet that was the center o f the
Galactic Empire in the Foundation Trilogy. It was a passive,
dead planet completely sheathed in an encircling megalopolis, where sentient beings controlled everything and the basic
forces of nature were nowhere to be seen. In contrast, our
Earth is very much alive, geologically speaking, and its internal forces can never be mastered? A significant role for the
earthquake scientist is to help human society adapt to this
reality.
I close with a direct appeal to young scientists who
aspire to study earthquakes. You are fortunate to have chosen
a field where the distance between basic and applied science
is remarkably short. The pursuit of either aspect can lead to
an immensely rewarding and satisfying career. However, to
fully exploit the opportunities outlined in this article, you
must become deep-thinking individuals, capable of delving
into the most fundamental aspects of earthquake phenomena. While you should seek to apply your skills to the practical issues of hazard mitigation, you should try to avoid the
parochialism of a narrowly applied science. Go for the big
problems, answer the difficult questions that are the true
challenges of earthquake science. The N R C has recently
commissioned a Committee on the Science of Earthquakes,
which I chair, to articulate these challenges and to argue for
the resources that you will require. In this endeavor, we need
your help. Think about these questions and let me know
your thoughts. El
Thomas H. Jordan
Department of Earth, Atmospheric and Planetary Sciences
Massachusetts Institute of Technology
Cambridge, MA 02139, USA
Seismological Research Letters Volume 68, Number 2
[email protected]
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