skip to main content
Home  /  Interviews  /  Emile Okal

Emile Okal

Emile Okal

Professor of Geological Science, Emeritus, Northwestern University

By David Zierler, Director of the Caltech Heritage Project
April 5, 2022

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Tuesday, April 5, 2022. I am delighted to be here with Dr. Emile Okal. Emile, wonderful to be with you. Thank you for joining me today.

EMILE OKAL: Well, my pleasure. Thank you very much.

ZIERLER: To start, would you tell me your title and affiliation?

OKAL: My title is Professor, Emeritus at Northwestern University. I'm retired now, which means that I no longer teach, the Dean no longer pays me, and actually, I no longer have any students, whom I would take responsibility for mentoring into their PhD studies. However, I keep trying at least to be active in research because Mother Earth never stops giving us surprises, the most recent one being the Tonga volcanic explosion a couple of months ago. I'm not exactly retired in terms of my professional activity as such.

ZIERLER: Of all the different fields you're involved in, which one best describes what you do: seismology, geophysics, volcanology? What is the best word for your field of research?

OKAL: I would say it's geophysics with a very strong component of seismology. The reason for that is that most of what we know about the internal structure of the Earth has come from seismology, with all due respect to my colleagues who use other techniques. Seismic waves are probably our best way to illuminate the Earth and to penetrate it in order to retrieve information about its structure. Geophysics owes immensely to seismology. Now, I've also been involved, as you mentioned, with tsunamis fundamentally, and that's a direct consequence of my being mentored at Caltech informally by Professor Hiroo Kanamori, who, being Japanese, was particularly sensitive to the problem of tsunamis. I also delved into other things, hydroacoustics, which is the propagation of sound in the ocean, which is, in a sense, an application of seismology to a water column. Then, volcanology because I was involved in the study of various volcanic sources in the Pacific Ocean.

ZIERLER: Does your interest in geophysics and seismology go all the way back to France, or was this only something that you pursued once you got back to the United States?

OKAL: Actually, I was a physics major in France, and I was fortunate to have a summer job in 1969. I found a summer job at the University of Alberta in Canada as a member of a team which was actually doing geomagnetism in the Canadian Plains and the Rockies. We were driving a truck back and forth along the Trans-Canada Highway and U.S. 2 south of the border to deploy, maintain, and survey some geomagnetic stations under the leadership of Professor Ian Gough. I discovered at that time that you could do physics while enjoying the outdoors, and at the same time, enjoy physics on the scale of the Earth, which was directly accessible to the layperson, which didn't involve looking into micro or nanostructures, but which was tangible. You could touch it with your hands. This is what drove me, a couple of years later, to switch to geophysics and eventually to the Seismo Lab.

ZIERLER: What were your impressions when you first got to Caltech? Was the Seismo Lab something you had long wanted to be involved in?

OKAL: I had visited the Seismo Lab in 1973. I joined Caltech in 1974 as a graduate student, but I had visited in 1973, and I decided, towards the spring of 1974, to come to the United States for a PhD. And through a very fast decision, both on my part and that of the leadership of the Seismo Lab, I was admitted in early July of 1974.

ZIERLER: What were some of the big questions in the field when you got involved in the Seismology Lab?

OKAL: A big question in the mind of every seismologist there, a very enthusiastic area of research, was so-called earthquake prediction, which after 45 years or so, hasn't matured, despite some very interesting things. But we cannot predict earthquakes. I have colleagues, some of whom you will probably interview, who are going to tell you that this is for a simple reason, that there's a certain unpredictability inherent in the nature of earthquakes. It was an activity at the lab in which I participated. They were monitoring very, very precisely the variation with time of the propagation of seismic waves in California. We were using quarry blasts. At the Seismo Lab, there were a bunch of people working with quarry blast operators, and they would give us very precise location and timing of their blasts. We, the graduate students, would be in charge of deploying seismometers at precisely the same stations to record them, then the scientists were involved in trying to see if there was a change in velocity with time, which hopefully, they could interpret as a change in the properties of the rock, which somehow would point out to an imminent earthquake. My role in this was just to drive my old 1965 Pontiac, to these stations out in the desert and instrument them very precisely. There was an army of graduate students who were on duty those days when the quarries were blasting.

ZIERLER: What were the connections between the Seismo Lab and GPS, the division as a whole?

OKAL: [Laugh] To say the least, we were very obscure.

ZIERLER: Meaning that the Seismo Lab operated like an island, so to speak?

OKAL: Well, it was a headland, if I may say. When I visited in 1973, it was still an island at the old lab back in the Hills, which had been the office of Gutenberg, Richter, and so on. But when I arrived at the lab in August, 1974, they had just moved to the new structure on campus. One of the reasons for that was to have more modern facilities, but another reason was that they were looking forward to more interaction with the division, with geologists on campus. They built it so that there was this connecting corridor, which would go through the library between I think Old Mudd and New Mudd. We had direct access to the geologists. I suppose we were so busy, frankly, doing our seismology, that we very seldom had much interaction with the geochemists in particular and a few geologists. We were taking some classes, but we were so busy that there was little interaction.

And that was quite regrettable because it took me becoming a faculty member later on in a different university in order to realize what the contributions of people like Gerry Wasserburg had been, and I mention him as an example because he was on my qualifiers committee. But I didn't have much idea about what Gerry Wasserburg was doing. An exception to this were the planetary scientists because they were also in a new lab on the first floor of the new Mudd Building. Also, we were living in some absolutely phenomenal times. I was there in 1976 when Viking landed on Mars, and we had, in a sense, been involved. Don Anderson was, of course, very strongly involved with the seismology experiment on Viking, even though it didn't work exactly as planned. And for example, I'd written a paper developed from a term paper I wrote in Don Anderson's class on building seismological tables, travel time tables, from Mars from scratch, from a couple of values we had, an estimation of the moment of inertia, mass, and so on.

These things sat completely unused for 40 years, and it's only very recently that, with the Insight Mission, we had some insight [Laugh], some data to infer something about the structure of Mars. To my great surprise, I found out that the new models they have for Mars were within the range of the models I had written in that paper. Another phenomenal result was the beginning of the Voyager missions, which was toward the end of my stay at Caltech, these missions to the outer planets of the solar system. It was somewhat different, but at some point, people discovered the rings of Uranus. I was there, and one day, "Wow, Uranus has some rings." That was from the occultation of a star during an earth-based observation of Uranus. And within 24 hours, Peter Goldreich had written a theory of why Uranus should have rings. [Laugh] We were pretty close to the JPL people. And there was so much going at the time in terms of planetary exploration.

ZIERLER: Who was your thesis advisor at Caltech?

OKAL: My thesis advisor, in the end, turned out to be David Harkrider. But I worked very independently and with many, many people. At the beginning, I started a project with Don Helmberger, but it never materialized. For some reason, I looked at looked at different pastures as having greener grass. I worked a lot, at some point, with Don Anderson. I was influenced enormously by Hiroo Kanamori because he really captivated a number of us with a combination of his theoretical power and his absolutely exceptional observational skills. I remember Hiroo used to go home for dinner, then come back around 7 or 7:30 pm, and we would stay with him until close to 11 o'clock or midnight, and he would just motivate us with ideas. We would spend the whole night at the computing center. In those days, you had a computing center, and everything was in batch mode, where you would submit a job with punched cards and all that. During the night, turnaround time was much faster, so we would really work at night. We'd stay up at night and, in a sense, go home at 6 or 7 o'clock in the morning completely exhausted. By the time we would show up at the lab around 10 or 11 in the morning, if not later, we would go back, and see Hiroo, and tell him, "Hey, remember what you talked about last night? Here are the results." [Laugh] By the way, we were spoiled with the fact that we had 24-hour operations. The computing center was open all night.

I think the Millikan Library closed for a few hours between 3 o'clock in the morning and 7 or so. Also, in California as opposed to Europe, where I was coming from, you had stores open 24 hours a day, you could go and have breakfast in coffeeshops 24 hours a day. Especially in the last year of my residence at Caltech, when I didn't have to take any classes or TA for any classes, I had absolutely no constraints, so I was going to bed when I was exhausted and collapsing. I discovered that my body rhythm was actually based on a little longer than 24 hours. People who go spelunking in caves where they don't see the sun and so on find the same thing. Every day, I was going to bed one hour later, which meant in the end, I had some beats with the rest of society, which had a kind of monthly or lunar period of some kind, and I'd get up when other people would go to bed. Otherwise, I would be in phase a few weeks later and so on.

ZIERLER: In the way that you emphasized Professor Kanamori's theoretical and observational skills, is that to say that at the time, and even today, seismology does not have strong distinctions between experiment and theory in the way that, say, particle physics does?

OKAL: I'm not too familiar with particle physics, and I would like to emphasize that what I described of Professor Kanamori were superb qualities, but they were certainly shared by the other faculty members. Perhaps, the fact that he was also available very late at night led us to have somewhat deeper interaction. But certainly, his colleagues were also superb theoreticians, like Harkrider or Helmberger. They also had a very keen eye for data. I'm thinking, for example, of Helmberger, who really had a sense of the wiggle in the seismogram and what it meant, which was quite remarkable, mostly at the high-frequency end of the spectrum. But I cannot really compare things much with areas such as theoretical physics. But I think it actually goes back a bit to what you asked me before, where I told you that the great thing with geophysics as a part of physics is that you deal with a system which is tangible and accessible. With all due respect to the scientists who deal with nanoseconds or light years, we in seismology were measuring minutes and seconds. This is something that comes close to human life, in a sense.

ZIERLER: Was the Seismo Lab institutionally connected beyond Pasadena? In other words, did it work closely with the USGS or other university laboratories?

OKAL: The USGS came to campus, I think in my last year at the Seismo Lab. They opened the Pasadena branch, which was, and I suppose still is, across the street. But before that, of course, there were collaborations with the USGS. I remember a British post-doc who was flying up to Menlo Park all the time. There were other collaborations. However, they grew, certainly, much more intensely when the USGS opened the Pasadena office. Then, we had connections at other universities. Certainly, our faculty were very close to faculty at other universities, if for no other reason that in many cases, the junior colleagues at the other universities were Caltech graduates. [Laugh] But also, there were good connections with the senior faculty. With students, there was a feeling of healthy competition, perhaps with the students at the other universities because let's face it–and this was actually written superbly by Bill Menard in his book, Oceans–when you have a ripe scientific problem, it will be attacked by different groups just because it's there. The classical examples in plate tectonics, when plate tectonics was about ripe, you had the famous Jason Morgan/Dan McKenzie competition. Our relationship with the graduate students at other institutions was a bit one of competition. But it was very healthy competition, and it has made for some good friendships down the line.

ZIERLER: When you were a graduate student, what was the state of the nation field on plate tectonics?

OKAL: That's a very good question. The state of the nation field, and maybe the state of the theory worldwide, was that it was pretty much accepted, but for a couple of absolute diehards, Sir Harold Jeffreys, for one, who was only at the time approximately 75 years old, and a Russian scientist by the name of Belousov, who was still pushing the theory of the oceanization of the continental crusts, which was that the continents would sink, and as they did, they would become ocean. But these were really exceptions. It was essentially the basis, interestingly enough, for the research we were doing. But I wouldn't say it was the Book because nobody had really found the time to write big books on it. People were too active and just kept doing research. And surprisingly, at Caltech, I never had a class on plate tectonics. This was something which was explained on notepads, on chalkboards, and so on, but we need ever had a formal class in plate tectonics. When I moved to a faculty position, the first thing I did was to try to put together a class on plate tectonics. How do we know what we know about plate tectonics? Towards the end of my career, it had evolved into something like a 700-page set of notes, to which I gave the title, Everything You Always Wanted to Know about Plate Tectonics but Were Afraid to Ask.

ZIERLER: Was the science of continental drift already settled at that point?

OKAL: Yes, the idea of continental drift was, in terms of the continents themselves without any reference to the oceans or seafloor spreading, which is part of the same business, but a slightly different idea. The idea of passive continents drifting around was laid down by paleomagnetic studies in the early 60s, the work of people like Allan Cox and so on. It was accepted, yes.

ZIERLER: I wonder if you can explain how continental drift can be accepted science while plate tectonics was still under some level of debate. What's the understanding there?

OKAL: I think the idea of continental drift is fundamentally an observational one, which goes back all the way to Wegener and even before that. I did some research at some point, and you'd be amazed to find that some of the mapmakers of the 16th century noticed the coherence of shape between South America and Africa, and you can find notes there referring to them have been separated. And then, Lomonosov, in Russia in the 18th century, was perhaps one of the most enlightened people in science in the 18th century. He clearly wrote somewhere that there was a motion of the big masses. This is an observational thing that the continents had drifted, for all kinds of reasons, be it their shape, the presence of some paleontological evidence, paleoclimatic erosional evidence from glaciers, or the paleomagnetic evidence that came later. These are observations called continental drift.

We asked, "Why?" This is what led to the scientific demise of poor Alfred Wegener, which is that people like Harold Jeffreys asked him, "Why do the continents move?" This is something I used to teach my students. If you're asked a question you cannot answer, don't try to BS your committee by providing some fuzzy answer because they'll nail you down. This is exactly what happened to Wegener. Jeffreys told him, "If you tell us that the continents move, what drives them?" Instead of saying, "I don't have the slightest idea, but I think they move," he said, "Well, it may be a tidal force," and Jeffreys wasted no time showing that the influence of the tides was six orders of magnitude too small or so. Poor Wegener was ridiculed by the rather stuffy members of the Royal Society in England and people like that, because instead of saying, "I don't have the slightest idea," he tried to make an answer up. Plate tectonics really came alive when people said, "This could be convection. If it's convection, there has to be an upwelling somewhere and a downwelling somewhere." It became a dynamic theory instead of purely a static observational one, a kinematic one.

ZIERLER: When you were at the Seismo Lab, was it a center of scholarship where researchers from all over the world would come visit, do research, give seminars? Was it a magnet, so to speak?

OKAL: It was a beehive, it was a magnet. We had visitors coming. I mentioned Belousov, of course, but just before him, we had Tuzo Wilson, one of the people who explained the concept of a transform fault in the oceans and the theory of hotspots. Then, we had an infinite stream of very distinguished scientists from Japan because Hiroo Kanamori, at the time, was still a rather recent addition to the Seismo Lab. He had come to Caltech from Japan, I think in '72 or so. We had an infinite stream of post-docs like Yoshio Fukao, visiting professors, young scholars who had been Kanamori's students like Katsuyuki Abe, Niko Shimazaki was a post-doc also, then Seiya Uyeda, who was a very senior, very distinguished professor at Tokyo University, also visited for a while. Yes, we had a string of visitors. We had weekly seminars, like pretty much every department has. We had plenty of very distinguished visitors.

ZIERLER: What did you work on for your thesis research?

OKAL: All kinds of things. Actually, I think I initially started working in studies of lateral inhomogeneities the earth, but not really very formally. Eventually, there were more systematic methods like tomography. We were doing more pointed studies with perhaps more elementary means, so I started working on lateral inhomogeneities between continents and oceans using so-called ScS waves bouncing between the core and the Earth's surface. In parallel, I worked on the dispersion of very long-period mantle waves. That was one part of my thesis. Then, the second part, I was fascinated by the theory of the normal modes of the earth, the free oscillations of the earth. I worked on some questions, which were particularly well-approached using normal mode theory, and one of them was the matter of exactly what happens at the core-mantle boundary, trying to unravel the properties of the mantle as it approaches the core. This was one chapter of my thesis, which later, when I was at Northwestern, my student, Michael Wysession, prolonged and essentially improved very much on whatever I had done in this respect.

Another thing that kept me active on and off for 40 years, and to this day, I used normal mode theory in collaboration with Robert Geller, who's now in Japan, to try to solve this problem of whether or not deep earthquakes had implosive components to their source, which was something that had been proposed by Freeman Gilbert at Scripps and Adam Dziewonski at Harvard. Geller and I showed that there were some artifacts of the procedure that meant that the results were questionable in the particular case of the Colombian earthquake of 1970. When I think of it, these were very daring acts, in a sense, or suggestions from the part of two graduate students at Caltech at the time. We were essentially confronting very distinguished, very senior scientists at the time, which earned us the comment from Freeman Gilbert, which was reported to us by one of his students' at Scripps. Freeman had mentioned us one day as, "Those young punks up the road at Caltech." [Laugh]

But in the end, it took 40 years because large, deep earthquakes are extremely rare. There's one probably every ten years or so, and we also benefit from much better equipment, data collection methodologies, and logistics. But where I stand now, and this was part of the PhD thesis of my last student, Nooshin Saloor, is that Freeman and Adam were right that deep earthquakes can have isotropic components, which represents a collapse of a metastable crystalline structure into a high-pressure phase, but we were also right that the evidence for it in the Colombian earthquake was artificial. This project is still open in my mind because in her thesis, Nooshin showed that some of these earthquakes do and some do not, and we don't understand which do and do not for one good reason. We now have perhaps five earthquakes which were big and deep enough to lend themselves to this kind of research.

ZIERLER: What were the instruments most relevant for your thesis research? What did you need to make observations?

OKAL: I was a child, in a sense, of the WWSSN, the World-Wide Standardized Seismic Network. These instruments were rather traditional in that their concept went back to Prince Golitsyn in the 1900s in Russia, who had the idea of the electromagnetic seismograph. The WWSSN instruments were nothing but developments, notably by Frank Press and Maurice Ewing. But fundamentally, the infrastructure remained the same. You had an electromagnetic seismograph, which used a galvanometer to write on a daily sheet of photographic paper, which was then chemically fixed, and so on. In my last years at Caltech, I witnessed the beginning of a transition to digital instrumentation, which in those days, consisted really of adding an analog-to-digital converter to these instruments. But the mechanics of the instruments remained the same, they were just putting a box there to provide recording on digital media. The thing really changed just about the early 80s, when they developed instruments, which were much broader band and coupled to the same kind of digital recorder.

One other thing I should say, from the 30s to the 50s, Caltech had really been at the forefront of the development of instrumentation in seismology, and the name attached to this is Hugo Benioff, who was already dead when I joined the lab. But Benioff did two things, he pushed the electromagnetic seismograph that had been invented by Golitsyn to its limits. He managed to play with the period, the feedback, and all that to develop these absolutely superb instruments, some of which were broadband before their time. Then, he worked on a different kind of instrument, the famous Benioff strainmeters, which were enormous rods, essentially, deployed in the basement of the old lab in the Hills of Pasadena but close to campus. These instruments were really unique because they had phenomenal long-period capabilities. Some of us benefitted from digging in the archives at Caltech. I remember, in those days, all the archives were in one of the buildings of the old lab, the so-called Kresge Building, which still belonged to Caltech at the time, and which served as a laboratory where they kept the strainmeters and other seismic instruments in the basement.

It also served as an archival facility, where they had all the paper records on shelves. We would go there and spend time just moving boxes around and looking at everything, which contained a treasure trove of data. By the way, they still contain it, but all the archives at Caltech are now rotting in tractor trailer containers, which are somewhere in a flood plain of the Sacramento River in Sacramento, next to the pound where the California Highway Patrol keeps their cruisers that are involved in accidents and below the levees of the Sacramento River. I've tried to get involved in various attempts to salvage these records, which are threatened with shredding, but it's very, very difficult to convince the administrators that these things have value and are absolutely unique records, and that some means of preserving them should be engineered.

ZIERLER: In what ways did the Seismo Lab use computers when you were a graduate student?

OKAL: In the ways of the 70s. [Laugh] First of all, computers were strictly in the business of number-crunching. In-house, we had an old machine called a Bendix, which operated, believe it or not, with tubes. The electronics were all based on vacuum tubes. This thing was used to closely locate a few earthquakes by using something like 30 stations. Nowadays, they use something like 600. The only person who managed somehow to use the Bendix was an old gentleman by the name of John Nordquist, who I think is thanked in Richter's original paper in 1935 on magnitudes. He thanks John Nordquist for helping him draft some figures. That gives you an idea of how senior this person was. Then, we had a little in-house computer for which there was a lot of competition. Essentially, only one person could use it at one time, and it was swallowing punched cards. We used to keypunch code on machines which made incredible noise. For anything else, we would depend on the mainframe timeshare machines, which were on campus at the computing center, and actually also read punched cards.

There was a computing center facility, which was shared by the whole institute. There was no such thing as personal computers or even departmental computers. The first departmental computer arrived at the lab, I think, two weeks after I left in 1978. These were research computers. Regarding observational computers, which would digest the data that was brought in from various stations, there was very little available. If I remember well, when I was there, most of the data streaming from the Network, which was growing more and more, was in the form of radio signals over radio links or telephone lines, then being recorded on paper or on what was known as develocorders, which were essentially microfilms streaming through machines that were injected with chemicals, a little bit like intravenous feeding of patients in hospitals, then kept as film rolls. But there was very little involvement of computers in the recording of the Network. I left at a very critical time in 1978, when all of this was evolving at a very rapid pace. A couple years later, I think all the recording was made on computers.

ZIERLER: Either scientifically or administratively, when you were a graduate student, was there a single individual at the Seismo Lab you considered a leader who really set the tone for what the Lab was doing during those years?

OKAL: This is an extremely difficult question. Scientifically, it was very clear that there were a number of absolutely superb faculty. I mentioned Hiroo Kanamori, Don Anderson, Don Helmberger, David Harkrider, and so on. There were people like Tom Ahrens, who was working on a different aspect of geophysics, which was shockwaves, properties of minerals at high pressures and temperatures, and so on. There were several brilliant, superb faculty members who were leaders in some fields, pretty much all of them. I don't think it would be easy to answer that question. From the administrative point of view, I would say we were absolutely spoiled as graduate students, which is a common situation for graduate students, and it should be such, I think. By this, I mean that we never really had to worry about our welfare, so to speak. We were all paid miserable wages, and that was the name of the game, which motivates you to graduate reasonably quickly, otherwise you'd probably stay until you could get tenure as a graduate student, if not emeritus status. [Laugh] But what I'm saying is, these were easy times.

The money was flowing, in a sense. Not very much into our pockets because it's not supposed to. Graduate students are not supposed to earn much money. But the finances of the Lab itself were taken care of by administrators, faculty, and the leadership of the Lab, so that we didn't have to worry about it. There was money for this and that, to a large extent, there was money to send us to professional meetings. There was a whole procedure by which this computer center was supposed to charge the various departments by the number of CPU minutes, lines printed, and so on. But somehow, the money was flowing. Of course, that means there was somebody there who was raising the money. In those days, compared with now, I realize how much easier it was, but the job was superbly done by all the faculty members who were very successful at writing grants and getting money, but also by the director, Don Anderson at the time, who was the towering figure there in terms of making sure the Lab was run. Administratively, the leader was the director, and the director, I suppose, was doing a good job because he remained the leader for many, many years. The Lab was prosperous, and I suppose I can say it was very well-run.

ZIERLER: For the last part of our talk, I'd like to ask a few retrospective questions, both about the Lab's impact on your career and on the field in general. As a result of you being a graduate student at the Seismo Lab, what were you allowed to do, in terms of the jobs available to you, the research projects and collaborations you were able to take on, subsequent to your time at Caltech?

OKAL: Well, it was the mother's milk. [Laugh] I was spoiled by the fact that I was given an education, I was allured to areas of research, and I was given the means to grow and develop, then transition into a faculty member. In terms of the positions, these were also very different times because many of us didn't even go through a post-doc. Many of us at the Lab would have an assistant professorship waiting for them when they graduated. I was certainly very fortunate that was the case for me. This was the result of the environment at the Lab, and the fact that we were sent to professional meetings where faculty from other schools would look at us, as well as the fact that the faculty and the leadership of the Lab would make sure to follow our efforts to get positions and recommend us. This is how I got a job at Yale University. I had a job offer even before I defended my thesis. I accepted it after I had defended. This was 44 years ago, in March of 1978. I started as a faculty member in September. Those were the days in terms of research areas. To be absolutely fair, I think my colleagues and friends who were graduate students at MIT, Scripps, or the big schools, and perhaps some of the not-so-big schools, were similarly educated and mentored by their respective faculties. It wasn't really terribly exceptional that the Lab would do this for us. In terms of research projects, I was exposed to various areas of research, which I sort of naturally followed. When other opportunities came up and science evolved, I'd been given the education, the means, and the skills to recognize these areas and to tackle them.

ZIERLER: As you went off into the world beyond Caltech and got a greater, wider appreciation of the field, what did you learn and appreciate about the Seismo Lab's influence in geophysics and seismology?

OKAL: I think what I learned to appreciate was, perhaps most of all, the opportunity we were given. As I said, it was a beehive, a place where I spent four extremely happy years. Not everything was rosy every day, but when I look back, I realize that these were very, very happy years that I spent there.

ZIERLER: Finally, last question. To the extent that you've kept up with the Seismo Lab over the years, I wonder if you can reflect on how it's changed and how it's remained the same since you were a graduate student.

OKAL: Well, it's changed because, of all the people I knew there, I think only Hiroo Kanamori is still alive and active. Certainly, the faces are not the same. The subjects are not the same. The leadership is different. But science has changed also. I would like to think that the excellence in the education and research dispensed and provided there have remained at the same level. I think also, and this is something which transcends the question of Caltech and addresses the question of academia as a whole, I think one component, which hasn't changed, I hope, is the absolutely complete academic freedom I was fortunate to enjoy both there and in the rest of my career. To reflect on that, we were, of course, involved with various research projects, which were the responsibility of faculty members, but we were absolutely free to do whatever we pleased in terms of research. We were free to embark on anything.

And that is something that is the basis of academia, known as academic freedom, which goes hand-in-hand with, at the faculty level, the principle of tenure, where essentially, once you prove yourself and achieve tenure in an academic position, you're told, "We like you, we trust you. Do whatever you want, within reasonable margins, of course." That's the essential ingredient of research creativity. I must say that as my life is advancing, and I'm now retired, I would like to hope that the next generations will enjoy the same level of academic freedom both at the faculty and student levels. It's probably part of the process of aging to reflect on old times and to be concerned about some developments that can be identified in the changing times, but that would be my concern for the academic environment in the years to come.

ZIERLER: And it's a hallmark in your memory that at the Seismo Lab, at Caltech when you were there, academic freedom was of utmost importance.

OKAL: Oh, yes. It was not only of great importance, but it was unquestioned. It went without saying. It was so much part of the principles that we took it for granted.

ZIERLER: On that note, this has been a wonderful conversation. I'm so glad we were able to engage in your reflections of the Seismo Lab. I'd like to thank you so much.

OKAL: Thank you very much.