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Photo courtesy Caltech
Interviewed by Karen Brown for the
SCEC Quarterly Newsletter
.
SQN:
You attended Bates
College and then Indiana
University where you majored
in physics and mathematics.
How did your interest in
physics and math arise?
TH:
I knew I was inter-
ested in science. I have always
been interested in how things
work, and I was at various
times a chemistry major, a
physics major, and a math
major. It was sort of a process
of elimination. The premeds
drove me out of chemistry, and
mathematics didn’t seem to
have enough applications, so I
ended up in physics.
SQN:
You went on to do a
Ph.D. at Caltech in both
geophysics and applied
mechanical engineering. Were
these two subjects unusual and
unlikely partners?
TH:
No, actually they’re
very closely related. To me,
applied mechanics is more
about the mechanics of
continuous media. I took
several classes in elasticity, and
they were very useful in
geophysics.
SQN:
The combination of
subjects also is reflected here in
your position at Caltech. You
have joint positions in the
divisions of Engineering and
Applied Sciences and Earth
and Planetary Sciences. Is that
a first?
SQN:
How do your
colleagues and others view
your joint position?
TH:
It means that you
have twice as many contacts. It
means there are twice as many
colleagues to learn the names
of and what they do. There’s
often twice as much jargon to
learn. Procedures in the
different divisions are differ-
ent—how people are tested
and what’s expected of them.
There are different journals and
meetings and committees...
SQN:
How do you keep
up with all of those?
TH:
I guess the answer is
that I don’t. It’s almost
impossible to keep up with all
those different things, and yet
you have to keep up with at
least some fair percentage of
them. So it definitely makes life
more complicated, and it
makes it harder to focus on
some individual problem.
SQN:
Are there positive
aspects?
confusing, I’m willing to find
satisfaction in confusion.
SQN:
Is there ever any
misunderstanding between
seismologists and engineers
about the size, nature, and
dynamics of earthquakes?
TH:
Certainly; we come
from two entirely different
perspectives and universes
when it comes to how we view
the earthquake problem.
Seismologists look at the
overall process of the earth in
the long term: how did it get
the way it is?
In that viewpoint often the
biggest events are the ones that
matter the most. We have a
range of sizes of things, and in
the earth sciences it often turns
out that the very biggest
examples of something
dominate how the final form
looks. So we cannot ignore the
big events in seismology. And,
in fact, in some ways they’re
the ones we have to really
understand because they
dominate processes like plate
tectonics.
In the engineering world the
perspective is usually “What
have we learned from our
recent past about buildings
similar to the ones we’re
putting up now, and how can
we improve our current
buildings?”
engineering point of view,
they’re viewed as the extreme
and rare occurrences. Often
they’re viewed as something
that should not dominate our
thought in terms of how to
respond to them. However, for
an earth scientist, those large
events are the key actor.
SQN:
Have you found it at
all difficult to reconcile these
different motivations?
TH:
I find that there is a
tremendous inconsistency
between the earth science field
and the earthquake engineer-
ing field in terms of how we
view large earthquakes. It’s my
own view that large earth-
quakes are infrequent but
inevitable. When they do occur,
which they inevitably will, we
may look very foolish if we
have not diligently studied
what those large earthquakes
will be like.
That is, if we get another 1906
earthquake and we say we’re
completely surprised by what
happens, then we will look
very foolish, because people
will say, “You knew such an
earthquake was going to
happen; you’ve been telling us
it’s going to happen.” So the
engineering field needs to
understand what such an
earthquake will look like.
Thomas Heaton
Interview with SCEC scientist . . .
I think most people would consider that I’m a
seismologist. I’m not sure you’d want to actually
enter a building I designed.
TH:
Probably not. I think
Professor Bruce Bolt at the
University of California,
Berkeley has had a joint
position in engineering and
geophysics.
TH:
Oh, sure. One of the
great joys in life is seeing the
connections between recurring
themes. Many of the problems
and themes of engineering
show up in some different way
in seismology. And vice versa.
Overall, though, I would say
it’s a challenge. One of the
secrets to life is learning how to
find satisfaction in the things
around you. Although having
these two things going on is
The very largest events usually
have not happened in our
recent memory, and from an
SQN:
Are you really
saying that both fields need
each other?
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Professional Highlights
THOMAS H. HEATON
Education
Bates College, Maine
B.S., physics—Indiana University
Ph.D., geophysics; minor in applied mechanics—Caltech
Professional
Professor of Engineering Seismology, Caltech
Project chief, Southern California Seismographic Network Project
Member, ad hoc committee to plan a Southern California Earthquake
Center
Project chief, Southern California Earthquake Project
Scientist in charge, USGS Pasadena Field Office
Project chief, Northwest U.S. Seismic Risk Assessment Project
Research geophysicist, USGS Pasadena
Senior seismologist, Dames & Moore, 1978–1979
Honors
Faculty Associate, California Institute of Technology
Meritorious Service Award, U.S. Department of the Interior
Memberships
American Geophysical Union
Seismological Society of America (president, 1993-1995)
Earthquake Engineering Research Institute
California Universities for Research in Earthquake Engineering
Research Committee of PEER
Global Seismographic Network Committee of IRIS
Recent Research Subjects
Inversion of geophysical data to determine the rupture characteris-
tics of earthquakes
Simulation of strong ground motions for large earthquakes
Investigations of the physics of fault rupture and the state of stress
in the crust
Investigation of the radiation damping of buildings
Development of techniques for real-time seismology
Recent Publications
Heaton, T. H., J. Hall, D. Wald, and M. Halling. “Response of high-rise
and base-isolated buildings to a hypothetical M 7.0 blind thrust
earthquake.”
Science
267:206–211.
Kanamori, H., E. Hauksson, and T. Heaton. “Real-time seismology and
earthquake hazard mitigation.”
Nature
390:461–464.
Kanamori, H., D. L. Anderson, and T. Heaton. “Frictional melting
during the rupture of the 1994 Bolivian earthquake.”
Science
279:839–842
.
TH:
Oh, clearly, both fields
need each other. Sometimes the
earthquake seismologists make
many statements about the
sizes of earthquakes or the
occurrence of earthquakes that
leave the public with an
impression that earthquakes
are so violent that there’s no
way to deal with them.
And then you see from the
earthquake engineering
profession statements like,
“Well, our current codes are
adequate and we’re doing the
correct things.” At some point,
there’s a complete disconnect
between statements from
seismologists and those from
engineers. The truth is usually
somewhere in between.
SQN:
Do you look at
yourself as being more in either
camp?
TH:
I think most people
would consider that I’m a
seismologist. I’m not sure
you’d want to actually enter a
building I designed.
SQN:
Where did you go to
work following the completion
of your Ph.D. at Caltech in
1979?
TH:
For one year I worked
as an employee at Dames and
Moore. They’re a geotechnical/
engineering consulting firm. At
the time (1978-79), a large part
of their business was working
on nuclear power plants or
other types of energy facility.
research. Then I decided it was
hard to do research on a half-
time basis, and when the USGS
offered me a position to do
research full time in the
Pasadena office, I took it.
SQN:
How did you enjoy
the private-sector work?
TH:
It was a very high-
pressure world of geotechnical
consulting. Lots of immediate
deadlines and reports that had
to be done right away. It didn’t
really allow a tremendous
amount of time for in-depth
study of an issue. But at the
same time it was very challeng-
ing and rewarding. I only have
good things to say about the
people I worked with and the
things that they do. I just really
wanted to get back to research.
SQN:
Did the private
sector experience, although
relatively brief, affect your
subsequent career, views, or
approach?
TH:
It certainly gave me a
lot of connections with groups
of people that I might not
normally have had without
going into the consulting
world. And I think that
probably ultimately led to my
getting a joint appointment in
civil engineering.
SQN:
What was it about
research that attracted you
back?
I’ve seen three generations of seismologists go
to their graves saying, “It’s coming, it’s coming.”
You get a little skeptical after a while.
I had an unusual position. I
worked half time in the
Westwood office and for the
other half I was stationed at
Caltech to continue my
TH:
I think the greatest joy
is in seeing how things work
and how they connect together.
I can really say that I have
lived for those eureka mo-
ments, where you can see how
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things connect. That to me is
the most rewarding part of
professional life.
SQN:
What were some
eureka moments that you will
never forget?
TH:
I think that the
realization of how important
pulses are in the propagation
of rupture on faults was
probably the most exciting
time for me. That was about
1988.
More recently it’s been quite
exciting to understand better
what the brittle nature of the
crust is and how dynamic
rupture plays into the brittle-
ness of the crust. I haven’t
written that up yet.
Also, I think the time, in about
1993, when Professor John Hall
and I were looking down from
the top of an 80-story building
in Los Angeles and discussing
the physics of how the building
stays up in the air. There was a
moment of realization that
there were many assumptions
made in designing the building
that might not be consistent
with things that I knew about
ground motion.
In addition, there have been a
series of exciting developments
about the Cascadia subduction
zone problem. The first
discussions with Hiroo
Kanamori about Cascadia and
how it relates to other subduc-
tion zones were very exciting.
And then the correspondence
between me and Brian Atwater,
who was a geologist actually
finding evidence for these large
earthquakes in the Cascadia
zone, has been very exciting, to
actually see someone discover
these events that Hiroo and I
speculated on.
termed the Heaton Pulse,
would you please explain your
idea in simple terms and how
this influences damage of
buildings?
TH:
Once I saw it, it
seemed so simple in my mind,
but certainly it wasn’t always
so simple to explain. Judging
from the puzzled looks of
colleagues and from some of
the reviews I got, evidently it’s
not so simple to explain. But
it’s one of those things, once
you see it, it seems like, “Well
of course, it can’t be any other
way. It works.”
The idea is that the fault moves
caterpillar-like. That is, when
there is slippage between the
two sides of a fault, only a
small part of a fault is moving
at any given time. And the
question then is Why does it
propagate as a pulse? The
simple answer is that the
friction is temporarily low on
the fault for dynamic reasons.
In effect, part of the eureka is
that we’ve been searching for
some explanation of why faults
are so weak, and this slip pulse
mechanism seems to require a
weak fault for its existence.
plausible explanations. I’m
currently quite attracted to the
explanation that Joe Andrews
and Yehuda Ben Zion have
come up with about material
unconformities being respon-
sible.
SQN:
You were scientist in
charge at the USGS Pasadena
office from 1985 until 1992, a
time when the office was a key
unit in responding to numer-
ous important earthquakes.
What was your contribution at
that time?
TH:
I pushed very hard to
change the focus of the seismo-
graphic network from a
network that was primarily
looking at patterns of occur-
and could be used for a variety
of purposes. One, for under-
standing how waves propagate
around California. Two, I was
very interested in seeing that
we would better be able to
predict motions in future
earthquakes for building
purposes. And three, I was
quite intrigued with the
possibility of actually coming
up with warnings of shaking
on its way.
So I pushed very hard to try to
get our network turned into a
practical tool for engineering
and emergency management,
whereas before the primary
purpose of the network was for
scientific research into patterns
of earthquakes.
It’s very satisfying now to see
that the network has evolved
into the TriNet Project, which is
really a tremendously historic
step ahead for seismology in
southern California.
SQN:
Please elaborate on
real-time seismology and your
contribution.
TH:
When I was scientist
in charge of the Pasadena
office, I certainly pushed in the
direction of improving the real-
time response of the network in
an earthquake. We were
probably the first network in
The result of the pulse-like motion that occurs close to a large earthquake can be seen in this
photo taken soon after the 1906 earthquake. Thomas Heaton points out that although the pulse
motion didn’t greatly damage the railroad station in the background, such a motion might have
serious consequences for some modern flexible buildings.
Collection of Carl Grove Gilbert, USGS, Menlo Park, CA
At some point, there’s a complete disconnect
between statements from seismologists and
those from engineers. The truth is usually
somewhere in between.
SQN:
Regarding the first
of these eureka moments,
which your colleagues have
The next kind of question is
Why is there dynamic weaken-
ing in the fault? Various people
have come up with several
the United States to put out
strong-motion instruments that
telemetered data in real time. I
was the lead author on a study
called the National Seismic
System Science Plan, which
fleshed out the vision for what
a new generation seismo-
graphic network could look
rence of earthquakes—
locations and times—to try to
come up with a system that
was more multifunctional.
I tried to modify the goals of
the network so that it would
actually record the three
components of ground shaking
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OFF-SCALE
AUTHORS
WHO
ARE
NOT
EARTH
SCIENTISTS
BUT
WISH
THEY
WERE
S
t. Francis of Assisi was by all accounts
a rich man’s son who squandered his
father’s money on wine, women, and
fancy armor for the Crusades. He had a vi-
sion one day—you could call it a spiritual
earthquake vision—and in the vision Christ
said to him, “Francis, dost thou not see my
house in ruins? Rebuild it for me.” It all de-
pends, as Bill Clinton would say, on what
you mean by the word “rebuild,” and, of
course, what you mean by “house.” The
politics of restoration, which are a large part
of the cultural politics in Italy, are not only
about the grandmother and the bell tower,
or about greater and lesser art; they are also
about class, and about memories of poverty
and contempt that no prosperity ever really
dulls. They are about who owns the future—
the Italians who made the past a misery for
so many other Italians or those other Ital-
ians, finally inheriting the earth—and they
can evoke a rancor so deep that most people
don’t even know they have it until an earth-
quake comes and shakes it out of them,
shakes the past to the surface.
“Most people don’
t even know they
have it until an earthquake comes and
shakes it out of them . . .”
[An excerpt from an essay about some of the lesser-known effects
of the series of earthquakes in northern Italy in 1997, best known
for destroying the church at Assisi.]
like if it were implemented in
the U.S.
As it turns out, we never could
excite management in Wash-
ington DC enough to follow up
on that vision, but we were
able to follow the vision closely
in southern California with the
TriNet Project. If you go back
to the original circular that was
written about 1989, it’s pretty
much a blueprint for TriNet.
Another contribution was
helping the Pasadena office to
become a more independent
operational unit. At one point
the earthquake program in
southern California was almost
entirely managed by the
USGS’s Menlo Park office. In
the 1980s we pushed to have
southern California become
more locally managed, both by
the USGS Pasadena office and
then ultimately by the forma-
tion of SCEC.
I would hardly claim credit for
the formation of the center, but
certainly I was in the mix when
the center came to be.
SQN:
You also served on
the board of directors and have
headed several committees.
Has SCEC fulfilled the vision
you had for it?
around to attempting that very
ambitious part of the project.
My vision of the center has
always been that it’s a political
necessity. That is, we’ve got a
number of institutions in
southern California that
absolutely require coordination
when we communicate with
the rest of society in terms of
policy decisions.
It’s like night and day between
having the center and the time
that we didn’t have it, in terms
of being able to speak with a
coherent single voice. In some
ways I think it’s probably been
the most important aspect of
the center. The ability to speak
with a consensus has given
great support to our scientific
studies.
SQN:
What’s the future
for SCEC?
TH:
Well, I’ve got to admit
I am somewhat concerned
about the future. The current
talk about broadening SCEC’s
regional focus into the entire
state of California and to
including far more research
groups concerns me. We may
lose some of that ability to
focus on issues that are of
importance to southern
California policymakers.
Without a center like SCEC, we’ll clearly have a
tremendous vacuum in how we communicate as
scientists with the rest of our society.
—Jane Kramer
“The Shock of the Old”
The New Yorker
, 2/8/99
TH:
I think SCEC has
largely fulfilled the vision.
Some of the aspects are
probably a little slower coming
than we originally envisioned.
In particular, we originally
envisioned having some
master stress model of the crust
in southern California, and I
think we are just now getting
There will still be a strong need
for southern California
institutions to communicate to
governments in southern
California, and I am somewhat
worried about whether the
future SCEC will be able to
fulfill that role, if in fact there is
any center at all. If we have no
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Heaton on Music and Motorcycles
There’s no doubt that Thomas Heaton enjoys the work he
does in geophysics and engineering, but it’s not the only
thing he’s passionate about.
Music is his other main interest, he says, adding that he
has been writing songs and playing the guitar “in various
forms” for 30 years.
He says that recently he added several more guitars to his
collection, which includes both electric and classical
instruments. He also has a small recording studio in his
living room.
“My mother is a professional musician, and it’s always
been just around the family,” he explains. “But even more
than that, I’ve always found music a way to travel
someplace else. It’s a way to close your eyes and just be
someplace else.”
But it’s more than just another way to relax. “Music is a
way to let something out that you didn’t even know was
there. While you’re playing music, emotions and things
pop out that you don’t even know were there.”
Heaton says music is like science in that it can provide for
him “those discovery moments. Music provides the same
kinds of surprises, in terms of things that you didn’t
really expect to find.”
Whereas for many years Heaton played music by himself,
he is now in a band at his church. “In many ways it’s been
an awakening to be able to play with a group of people.
That’s another new experience.”
Following hard on the heels of his love of music is the
thrill of the road in the form of motorcycle riding and a
special car—a red Corvette in his case.
Both the Corvette and a silver Honda Sport-Tour 1100
motorbike feature in framed photos on his office wall at
Caltech. Heaton says he has traveled 100,000 miles on
motorcycles over the past 30 years.
“The thing about motorcycling is it’s either very bad or
very good, but whatever, it’s memorable.”
Living as he does in the Los Angeles area, Heaton is no
stranger to freeway riding and finds it bearable. “It’s
somewhat frightening, but to be honest I think it’s really
important to live with a certain amount of fear. I think it’s
a rather pointless goal to constantly be searching for
safety, because in the end it evades you anyway.”
If anything terrifies him, it could be old age. Why?
“Because it’ll kill you,” he smiles.
center then we’ll clearly have a
tremendous vacuum in terms
of how we communicate as a
group of scientists with the rest
of our society.
Clearly that communication is
often strained. Policymakers
and the public in general have
a very difficult time talking to
individual scientists and
coming up with some sort of
reasonable view of what’s
going on. We really need
something like SCEC to help us
to communicate.
SQN:
Do you believe that
building codes in southern
California, and Los Angeles in
particular, are adequate to deal
with the expected large violent
earthquakes?
TH:
It’s rather interesting
that if an earthquake ruptures
as a pulse, then it turns out that
almost all of the energy
radiated in the earthquake is
contained in shear-wave
pulses. Rather amazingly, you
can show that those pulses are
also very important for flexible
buildings.
Understanding those pulses
has important implications for
some large buildings. Since we
haven’t observed the perfor-
mance of large buildings
together with very large
earthquakes, I feel that there is
great uncertainty about their
performance. However,
simulations of the response of
tall buildings to large earth-
quakes show that there is
reason for concern.
the ductile capacity of some
types of buildings, in particular
flexible buildings.
John Hall, Dave Wald, Marv
Halling, and I published a
couple of papers in which we
said that if you have a large
earthquake beneath a city, you
would expect to have many of
the flexible-frame buildings
damaged beyond repair, and in
many cases you might even
expect collapses of some of
these buildings.
That’s been quite controversial
because prior to our work,
people routinely said these are
the safest buildings to be in
during an earthquake. We
questioned whether or not
their performance would be
good in all situations.
SQN:
What has that led
to? Have you said there
shouldn’t be buildings beyond
a certain height constructed in
southern California, or made
recommendations about
building codes?
TH:
I’m glad you asked
that question. There have been
some reports that we have
called for a moratorium on
buildings taller than ten stories.
I know that John Hall has not
called for such a moratorium,
and I don’t believe that I have,
either.
We know that the energy in
very large earthquakes grows a
factor of 30 for every unit of
magnitude—so we can
anticipate that large earth-
quakes have much greater
energy. This energy can be
used to damage ductile
buildings. Our current building
code relies heavily on ductility.
Unfortunately, a large earth-
quake may severely challenge
I actually wrote a letter to the
Seismological Society of
America a couple of years ago
where I said, “We don’t
understand what happens to
large buildings in large
earthquakes, and perhaps we
should talk about a morato-
rium until we do understand.”
I wanted to emphasize to
people that we’re not quite
sure what we’re doing here.
I think Ken Reich of the
L.A.
Times
picked up on that letter,
and somehow it ended up in
the
L.A. Times
that I was
actively a proponent of putting
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a limitation on the height of
buildings. However, I don’t
think that a height limit is the
appropriate answer. It’s a
simplistic answer to a compli-
cated problem. And it certainly
irritated some people.
Our findings on the impor-
tance of near-source pulses
were pushed along by the
Northridge and Kobe earth-
quakes, both of which had
these large pulses in cities, and
the pulses did quite a bit of
damage to modern, flexible
buildings.
Neither of those was a very big
earthquake, though, so we still
point out that there could be
quite a bit bigger earthquakes
and bigger pulses.
I think the engineering
community, though, has at
least accepted that these are
real issues.
SQN:
Are you satisfied
that enough is being done to
try to resolve this matter?
TH:
No; no way. We’re not
even close. We’re building
these monstrous cities directly
atop earthquake regions,
spending literally trillions of
dollars building our cities, and
our effort to understand what
we’re doing is pitiful.
SQN:
Are you talking
about in the U.S. or around the
world?
whose performance in earth-
quakes is so uncertain.
SQN:
How do earthquake
codes vary around the world?
TH:
Codes are a very
complicated issue. There are
currently three codes in use in
the United States. There’s a
different code in Japan. The
codes have typically been
written to fix past problems.
That is, after an earthquake,
engineers study the perfor-
mance of buildings. When a
particular type of design
performed poorly, they say not
to do it again (by code modifi-
cations).
Some areas of the world don’t
use much of any code at all,
and any help that we can give
them is good. However,
sometimes it’s hard to transfer
our standard of living to other
parts of the world.
There is a lot of misunder-
standing, I think, of how the
different codes relate to each
other. I have often heard
people say that the Japanese
code and the U.S. codes are
comparable; however, after
looking at some of the work of
my colleague John Hall, it
doesn’t really seem that they’re
all that similar.
buildings, is quite a bit stricter
than the U.S. code.
SQN:
How come so many
people died in the Kobe
earthquake, in a country that is
wealthy by most standards?
TH:
I think the short
answer is that it was quite
intense shaking in a very
heavily populated area. In
contrast, we were quite
fortunate that the Northridge
earthquake occurred early in
the morning when our popula-
tion was largely in wooden
homes. Furthermore, the most
severely shaken regions in
Northridge were in the
suburbs, where almost all the
structures were residential
homes.
U.S. residential houses are
remarkably resilient in
earthquakes; our houses are
probably much better than
Japanese traditional houses.
Many Japanese people died in
their homes because Japanese
homes were not as resilient as
U.S. homes.
If the Northridge earthquake
had occurred in the middle of
the day, we would have had
more deaths, because people
would have been out in
buildings. In Japan they had a
lot of building collapses, too;
the very heavy shaking was
right under their buildings.
That’s not what happened in
Northridge.
that we know can collapse in
earthquakes. Certainly, to stand
around and say, “Well, that was
Japan; that couldn’t happen
here,” that would probably be
a mistake.
SQN:
You’ve been a
member since 1993 of the
Mayor ’s Blue Ribbon Panel on
Seismic Hazard Reduction for
the City of Los Angeles. How
has that work been?
TH:
It’s clear that one of
the greatest concerns for the
Los Angeles area is a class of
buildings called nonductile
concrete buildings. We had
collapses in the San Fernando
earthquake and in the
Northridge earthquake. We
had some near collapses in the
Whittier Narrows earthquake.
These are buildings that we
know can fail even in moderate
earthquakes.
Typically they’re concrete
buildings with frames—beams
and columns—that were built
prior to the mid-1970s. There
are many people working in
these buildings; there are
hundreds of these buildings in
Los Angeles, and they could be
a severe source of life loss in a
large earthquake in Los
Angeles.
Currently there’s no law that
requires that they be inspected,
strengthened, or retrofitted.
If you have a large earthquake beneath a city,
you would expect to have many of the flexible-
frame buildings damaged beyond repair.
However, I don’t think that a height limit is the
appropriate answer. It’s a simplistic answer to a
complicated problem.
We’re building these monstrous cities directly
atop earthquake regions, spending literally
trillions of dollars building our cities, and our
effort to understand what we’re doing is pitiful.
TH:
Around the world. It’s
really a rather amazing thing to
think that we would invest so
much in erecting structures
They’re written in such
different ways that it’s even
hard to compare them, but
when you design a building
under the Japanese code and
design a building under the
U.S. code, it turns out that the
Japanese code, at least for tall
But we probably shouldn’t be
too smug. We do have parts of
the United States, parts of Los
Angeles, where we have high
densities of people in buildings
There are procedures devel-
oped by the engineering
community to recognize and
strengthen these buildings, but
there are no laws that require
anybody to do anything about
them. I think they’re probably
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the most obvious problem area
that requires some policy and
legislative attention from the
City of Los Angeles.
SQN:
A lot of work has
been done on L.A. freeways
since Northridge. Are they
reasonably safe now?
TH:
Clearly the freeway
bridges as they were built in
the 1950s and 1960s were
inadequate to withstand
typical shaking in strong
earthquakes. The most obvious
problem seemed to be under-
sized columns with inadequate
shear strength and ductility.
Starting in the late 1980s,
Caltrans put together an
incredibly ambitious effort to
reinforce virtually every
column in every bridge in the
state. I must say I’m tremen-
dously impressed with the
diligence that Caltrans has put
into this problem. Whether or
not there will be any failures of
bridges in the future, it’s hard
to say. I just don’t know the
details. But clearly those
bridges are far better than they
were ten years ago. I am no
longer as concerned stopping
my car under a bridge as I was
ten years ago.
There are still some very
problematic structures for
Caltrans. With standard
bridges, you can reinforce the
columns, but for some of the
really large bridges, like the
Oakland Bay Bridge or San
Pedro’s Vincent Thomas Bridge
or Coronado Bridge in San
Diego, those are different kinds
of structures. I’m not sure
people have a good grasp of
what would happen to those
bridges in a very large magni-
tude earthquake.
TH:
Certainly there are
indications from the research
that we’ve done that say that
there may be some serious
problems. But I’m not in a
position to be able to tell you
exactly what kind of earth-
quakes we’re going to have
underneath Los Angeles or
exactly what’s going to happen
to the buildings. To do a test of
those buildings full-scale is
very difficult. There’s a
tremendous amount of work to
be done if we are to under-
stand the best strategies for
building structures to with-
stand earthquakes.
There are people working on
these problems, and they’re
good people. But considering
what’s at stake, I think we’re
spending a very small amount
on research compared with
what we’ve got at risk. We’re
not very high on the trade-off
curve between our research
costs and the cost of failures in
the system.
SQN:
Are we overdue for
a big quake in southern
California, or do we just not
know that?
coming.’ You get a little
skeptical after a while.”
The big earthquakes are
inevitable. There’s no question
about it, but compared with
our lifetime it could be any
time.
SQN:
What’s your view
on new data about slow
earthquakes and the implica-
tion for seismic hazard
assessment?
TH:
It’s clear that a lot of
the earth’s movement occurs so
slowly that we don’t see it on
seismometers or at least in the
normal range of seismometers.
We’ve long wondered whether
these slow processes happen
steady state or whether they
also happen in events that are
much slower than our normal
earthquakes.
It’s become clear that, at least
in some cases, they happen in
events. There have been several
of these events that have been
recorded over periods of days.
People were kind of hoping,
back when we were promising
to predict earthquakes, that we
would see such events prior to
the occurrence of large
earthquakes and that those
slow events would be diagnos-
tic of a coming large earth-
quake.
are slow events, at least on
some faults. Those slow events
were not followed by anything
large. Furthermore, our larger,
well-observed earthquakes
were not preceded by recogniz-
able slow events.
It may be that some of these
slow events actually are
followed by larger earth-
quakes. In fact, that’s what
probably happened in the
Chilean earthquake in 1960. It’s
a fascinating physical phenom-
enon that may teach us a lot
about the mechanics of the
crust, but I am not particularly
hopeful that it will allow us to
predict earthquakes.
SQN:
What direction is
your own research taking
lately?
TH:
I think what I find
most interesting at the moment
is understanding brittle failure
in the earth—the size-scaling
aspects of the strength of the
crust. There are lots of different
things being worked on, but
these days I work more
vicariously through students.
Before, when I was with the
USGS, it was easier to do my
own work. Now I try to
convince someone else to
follow up on ideas that have
been rattling around for a
while.
SQN:
Do you like teach-
ing?
TH:
I like to teach pro-
vided I have time to prepare
for the class. I like to teach; I’m
not sure that the students like
me to teach them! I enjoy doing
it. Probably it would be better
if I was better organized.
SQN:
You don’t feel
frustrated sometimes as a
teacher that you can’t get on
with your research?
It’s like night and day between having SCEC and
the time that we didn’t have it in terms of being
able to speak with a coherent single voice. In
some ways I think it’s probably been the most
important aspect of the center. The ability to
speak with a consensus has given great support
to our scientific studies.
SQN:
You read about the
potential here in Los Angeles
for a large violent earthquake.
It seems like an accident
waiting to happen.
TH:
In the pulse-type
model “overdue” is not a very
useful word. There was a
fellow here that I learned a lot
from—Ralph Gilman, who
worked at Caltech from 1930 to
about 1980. He told me: “Tom,
I’ve seen three generations of
seismologists go to their graves
saying, ‘It’s coming, it’s
In the past several decades,
observers have documented
convincing evidence that there
TH:
No, I like people.
Classes are full of people.