Home  /  Interviews  /  Leon Thomsen

Leon Thomsen

Leon Thomsen

Research Professor of Geophysics, University of Houston; Chief Scientist, Delta Geophysics; and Visiting Scientist, Lawrence Berkeley National Laboratory

By David Zierler, Director of the Caltech Heritage Project
April 21, 2022

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Thursday, April 21, 2022. I am delighted to be here with Dr. Leon Thomsen. Leon, it's great to be with you. Thank you for joining me today.

LEON THOMSEN: My pleasure.

ZIERLER: To start, would you tell me your current titles and institutional affiliations? And you'll notice I pluralize that because I notice you have more than one.

THOMSEN: I'm Research Professor of Geophysics at the University of Houston. That's a research position, without responsibility for the health of the program (because I'm retired now, and the tenured faculty have that responsibility). I'm also Chief Scientist of Delta Geophysics, which is a consulting firm I set up after I retired, 12 years ago. And when I'm in California, I'm a Visiting Scientist at Lawrence Berkeley Laboratory.

ZIERLER: I'd just like to say at the outset a note of congratulations for your induction into National Academy of Engineering this year. That must be a wonderful feeling.

THOMSEN: Well, that was, and it came as a big surprise, mainly because I'm not an engineer. But it turns out that the National Academy of Engineering is also for applied scientists. And that describes me pretty well.

ZIERLER: I'm curious, given that you've spent so much of your career in private industry, how many other scholars are there in the Academy that have a similar trajectory to yours?

THOMSEN: Well, the NAE has about 2,000 members, and it's organized into several disciplinary sections, one of which is the Earth Resources Section, numbering a couple of hundred, including me. And those are the people I'm most familiar with; I know maybe a dozen of those people. And I would say that in the National Academy of Engineering, as opposed to the National Academy of Science, there's probably a majority that has had a significant portion of its career in industry.

ZIERLER: I'd like to ask a few general questions about your research and career before we go back to your time at Caltech. First, perhaps at the broadest level, when you were working in private industry, did you feel like you were conducting scholarly research, just as you would if you were at an academic institution?

THOMSEN: Yes, I did, with the caveat that it was applied research, intended to eventually make money for the company. This research environment was central to the institution I was in. I began my industrial career in 1980, after ten years in the academic world, at the Research Center for Amoco Petroleum, in Tulsa, Oklahoma. It was a remarkable institution because of a number of remarkable men, who were responsible for attracting many talented researchers. Those men established a great research environment at the Research Center. I remember when I faced my first performance review at the end of the year. (They do a lot of that in private industry, planning projects, planning the way the staff is going to spend its time, then reviewing at the end of the year what you actually did, and how well.) At the end of that first year, my Supervisor said, "Leon, you didn't actually do much of anything of what we decided a year ago. But what you did do was great, so keep up the good work." That was an attitude established by the enlightened leadership of the Lab at that time.

Of course, we all charged our time to specific projects, hour by hour. Fortunately, for me, there was an official project called "Serendipity". I charged a lot of my time to Serendipity, and that was great because it allowed me to follow my nose. It had a tremendous monetary benefit for the corporation, at least potential benefits, which unhappily were not realized because the senior management at corporate headquarters in Chicago were not smart enough to realize that opportunity. They didn't trust the novel technology that we developed.

ZIERLER: What were the potential monetary benefits?

THOMSEN: We discovered that one of the fundamental assumptions we were using to explore for oil was wrong. Of course, we always had known it was wrong, but when I arrived, we learned how to deal with that. The incorrect assumption was that we could use the isotropic wave equation to design our field experiments and interpret them. But it turns out that rock formations are really anisotropic. I was a leader inside Amoco to understand that the departures of rocks from that simple model are profound, and this has profound implications for how we should design surveys and how we should interpret those surveys.

We learned in those days how to detect natural fractures in the subsurface. This was before anybody knew about creating fractures by fracking (jargon for intensive hydrofracturing). Rocks may be naturally fractured over millions of years of geologic time, and those fractures govern the flow of fluids in the subsurface, including the flow of oil and gas. It can be very important to understand where they are, how they're oriented, and so on. And we learned all of that in the early 1980s. Since then, those ideas have become public, and mainstream.

ZIERLER: I'm curious if Amoco took a page out of Bell Labs' playbook, where it was an industrial enterprise, but they supported basic science with or without regard for the company's bottom line.

THOMSEN: I think we did that implicitly. I don't think I ever heard the name Bell Labs mentioned at the Tulsa Research Center. But basically, we were the Bell Labs of the oil industry at that time.

ZIERLER: Of course, Exxon-Mobile created an industrial research center as well. Was Amoco ahead of them? Did they do this earlier?

THOMSEN: All oil companies in those days had research centers specifically designed to look down the road. Exxon's was one of the good ones. Probably next to Amoco, the best one was at Shell, in Holland. Sometimes they were ahead of us, sometimes behind. I can tell you an interesting story about that. We at Amoco discovered the facts of these ubiquitous occurrence of subsurface natural fractures and how to explore for them. We discovered that in the early ‘80s, and we kept that a secret for six long years. That was remarkable because people change companies, and secrets leak out; it was remarkable that we kept that secret for six years. At the very same time, the same ideas were being talked about publicly, in the context of earthquake prediction by a Scottish geophysicist. But nobody in the industry was paying attention to him.

In 1986, I was sent by Amoco to a continuing education course taught by a professor at Stanford. There were maybe 20 oil company participants. At a coffee break, the guy from Exxon came up to me and said, "Have you heard about this guy, Stuart Crampin ,in Scotland?" My ears went up, but I played cool and said, "Yes, I've heard about him." He said, "We've hired him as a consultant. We've been doing some field experiments based on his advice, and you know what? Everything he says is true."

Immediately, that same afternoon, I called back to Tulsa and said, "The cat is out of the bag. Exxon is listening to Crampin." We all had manuscripts prepared, sitting in our lower desk drawers, waiting for this opportunity. A week after I got back from this course, I hand-carried half a dozen scientific papers to the international headquarters of the Society of Exploration Geophysicists, which for historical reasons, is also in Tulsa. It was the deadline for the submission of presentations for the Annual Meeting. At 5 o'clock, I walked in the door and handed these papers to the receptionist, with a cover letter from Amoco management suggesting that they should organize a Special Technical Session at the Annual Meeting, coming up in a few months. We did that at the last minute, in order to corner for ourselves the credit for this breakthrough.

The receptionist accepted them without comment, and handed them on to the Technical Program Chair. He looked at them and said, "This looks interesting. I'm going to send these for review to my friend at Exxon." The guy at Exxon looked at them and thought, "Wow, Amoco is way ahead of us this time."

He called up the Technical Program Chair and said, "This is great stuff. You should organize a Special Technical Session with a high profile. But do you mind if we put in a couple of Exxon papers on this topic, even though the deadline has passed?" The Chairman said, "Sure, why not?" So, all our scheming was in vain.

The conference happened a few months later, in Houston at a building which no longer exists. The building had a metal roof, and that afternoon, there was a thunderstorm in Houston. The rain was coming down hard on the roof, and you couldn't even hear yourself think. I led off the Session, and gave an overview of our research. At a crucial moment, there was a peal of lightning and a crash of thunder. I looked to the heavens and said, "Hold your applause, please." [Laugh] It was a magical moment.

That Special Technical Session is remembered today, 50 years later; it's called the Amoco Anisotrophy Session. They misspelled it that way in the program, incorrectly, because hardly anybody knew the concept in those days. But that session unlocked a lot of research and subsequent development. Now, those ideas are mainstream.

ZIERLER: Having spent the initial part of your career after graduate school at academia at SUNY Binghamton, what compelled you to join Amoco? How much of a leap or adventure was it for you?

THOMSEN: It was a big adventure because it meant walking away from a tenured professorship to a 30-day contract. When I came back to Binghamton from my sabbatical, we discovered that campus politics was alive and well. A wag has said that campus disagreements among faculty can be so divisive and bitter because the stakes are so low. We got involved in some of that, and I got a little bit discouraged by that, like many professors.

But at that time, the oil industry was booming. Experienced people from big companies like Amoco and Exxon were being hired away by smaller companies, offering higher compensation. The large companies were replacing those experienced people with new hires from universities. Of course, they started their recruitment in the Southwest. Eventually, they got as far north as the State University of New York at Binghamton, where I was teaching, and they liked the quality of graduates we were producing, so they hired some. The next year, they'd come back with those kids in tow, now with one year of experience, and they would recruit the next cohort of graduates coming out the next year.

I would sit in the audience for these presentations, and the young professionals would talk about how much fun they were having. I thought, "Why should these kids have all the fun? I could do that." I held up my hand at one point, and they did hire me. It was a hire that probably wouldn't happen anymore because I didn't have any of the specific technical knowledge they require today. At that time at SUNY, I was interested in the deep interior of the earth and the properties of materials down there. I knew basically nothing about the oil business. But they were willing to hire me for two reasons. One, I could actually spell "geophysics," and two, my father was a well-regarded geophysicist for Amoco. On the basis of those attributes, they did hire me. Most oil companies would not make that mistake today("inappropriate technical preparation for that guy"). But all of my subsequent success came because of that difference in background. And I never regretted that move, despite the turbulence in the petroleum industry, during all those years.

ZIERLER: How much of a change was this career move for you in terms of your research agenda? Did you switch up fields, or were you able to continue what you were doing as a professor?

THOMSEN: I switched completely, because the technical issues are so different. But to answer that question better, maybe I should back up a little bit, to Caltech. My association with Caltech started in 1960, when I was an undergraduate. I came to Caltech expecting to major in nuclear physics, but in my sophomore year, I encountered Professor of Geology Bob Sharp. He was a fantastic teacher. At that point, I realized that I didn't like any of my physics professors, except for Richard Feynman, of course, but I liked all the geology faculty I met and the upperclassmen in geology. On that flimsy line of argument, I changed my major from nuclear physics to geophysics. I graduated in 1964.

I went to graduate school, since in those days, the Vietnam War was going on. It was important to stay in school, otherwise I would have soon been carrying a rifle through the jungle in Vietnam. I thought I could help my country better by being a productive scientist, so I applied for graduate school at Columbia, and was accepted (thus retaining my deferment from the military draft).

There, after various changes of focus, I did a PhD thesis in mineral physics. I did a post-doc in France and another post-doc at Caltech with the Seismo Lab. That brings me back to your focus, Seismo Lab history, so I'll say a few words about that. I was in the research group of Professor Tom Ahrens, who was a leading experimentalist in high-pressure mineral physics. He did an experiment that was never done before, nor since. In his lab, he had a naval gun with a barrel about 15-meters long. He fired projectiles through this barrel into a mineral sample at the end of the barrel. During the microseconds of the impact, he made x-ray measurements of pressure and density of the mineral. He was exploring experimentally the properties of the high-pressure minerals which exist in the lower mantle of the earth.

My job was to provide a theoretical complement to that experimental program. I had decided that my PhD thesis was a dead end, and I needed to approach this problem from a different viewpoint. Since the experiments were so difficult, I decided that the theoretical approach should be based on the most fundamental physics we know, relativistic quantum mechanics. I refreshed my understanding from previous course work, and I started to build a computer program to do the necessary calculations. I got funding for this from IBM, because they figured that if my research was successful, others would emulate it, more computers would be sold, and they would get their share of that business. They had a very enlightened view of academic research.

I built a program to do the calculations. In those days, computers were extremely expensive and slow, and with very limited memory, compared to today. The process was quite laborious, but I was making good progress, using the Seismo Lab computer. At one point, however, IBM said, "Why don't you come on up to Palo Alto on the weekends, and use our computer instead?" So, for a number of months, I would fly up there on Friday afternoon, live in a motel, and work all weekend intensively, using their computer, then fly back to Pasadena on Sunday evening. I carried my box of computer cards with me, north and south.

It was a big project. After I left Caltech, I worked on that at SUNY Binghamton for another six years. But in the end, I did not succeed in that project. The idea was to calculate the properties of minerals at high pressure, then compare those properties with the seismic velocities in the deep interior that we infer from seismic data received at the surface. The point was to decide what the earth is made of. I did not succeed at that. However, I'm pleased to report that nobody else has solved that problem either, in the last 50 years. So, part of the advice that I give to young people is: don't choose a problem which is too hard.

ZIERLER: What's so difficult? What eludes discovery after all these years?

THOMSEN: That's a good question. We like to think that relativistic quantum mechanics is really fundamental stuff. We like to think those guys know everything. But they don't. They have fudge factors in the theory, which happen because of the "many-body problem". People have known since the 1930s how to solve the two-body problem, say, a hydrogen atom with a nucleus and electron. But anything more complicated than that involves approximations. Of course, in a crystal, there are zillions of nuclei and electrons. At low pressures, these fudge factors can be evaluated experimentally, but at the high pressures of the lower mantle of the earth, they can't be measured, at least not in those days.

These days, people are much better experimentally than they used to be. For example, Professor Jackson in Caltech's Geological and Planetary Sciences Department, squeezes minerals very hard with pressures as high as what Tom Ahrens was doing, but she doesn't use a naval cannon, she uses just a small device, which squeezes the subject mineral between the points of two diamonds.

Imagine you have two diamonds pointing together, with a mineral sample at the point, and with a modest force on the outside. Because the points have such small area, she can generate enormous pressures at the points of those little diamonds with only modest forces on the outside. That's the technique today, but that was not possible in the late ‘60s and early '70s. I was not a good enough experimentalist to invent that technique.

The connection with my subsequent work, as I was doing this work, thinking about crystals, is that every single crystal is anisotropic. You can tell that when you look, for example, at a crystal of quartz. The external shape must be governed by the internal arrangement of atoms, and that must make for acoustic anisotropy of the quartz crystal. So, I knew about anisotropy when I came to Amoco. I got lucky since the very first dataset I ever looked at seriously showed unmistakable indications of anisotropy. I saw it when nobody else in the industry saw it, because they were imbued with isotropic ideas, and they didn't have a Caltech education. I was able to make progress there. It was a problem waiting to be solved. I made my entire career out of ideas emerging from that very first dataset that I saw.

ZIERLER: Tell me about the move from Tulsa to Houston. What did that change for you?

THOMSEN: That's a bit of a sad story. When I came to the Tulsa Research Center of Amoco, we had a very enlightened Vice President. He established policies that encouraged the research I told you about. Unfortunately, he got old and retired. People shouldn't do that, they should stay young. But he didn't. When he retired, he was replaced by a new Vice President for Research who brought in management ideas which stifled the creativity of the staff. One of the first things he did was to abolish the approved project of Serendipity. People started to leave. After a while, I decided to also leave.

I started looking for jobs outside Amoco in universities, because I was fairly well-known by that time, outside. But then, Amoco started a new group in the Exploration Department in Houston, created to apply Amoco's best technology to current exploration problems. Since I had been instrumental in creating many of these high-tech techniques, it was natural for me to join that applications team. It was a great experience. Even though I was in the Exploration Department, I had a boss who was extremely enlightened, and he managed all the funding problems for us. He arranged umbrella funding, so we never had to worry about money at all. He let us work on geophysics, not concerned with business process.

Let me tell you a story from that episode. We had a request from our office in Norway, "Would you please help us acquire, interpret, and understand a new type of data?" It was converted wave data, where the down-going wave was a P-wave, and the upcoming wave was a shear wave. They said, "We think that would help us with our problem here in Norway." We looked at this request and said, "Amoco has never done anything like that. This is not Exploration, this is Research. If we work on this, it would be stepping on the turf, and the toes, of the Vice President for Research. We'll pass this request on to our friends in Research, up in Tulsa." We did, and they replied, "That looks really interesting, but we can't do it because we've promised to do other projects, and if we don't do them, we'll be punished. We just can't do that." We reported this to my Supervisor in Houston. He said, "You guys are the only ones in the whole company who can do this. So, do what you think is best for the company, just keep me informed so I can get you the resources you need. Don't worry about the V0ice President of Research. If he complains about our violating his turf, let me handle it."

With that understanding, we proceeded to revolutionize the understanding of those kinds of data. Today, all such datasets are acquired and processed with the understanding we acquired back then, in ~1996. About the time I retired, years later, I learned that the Vice President of Research had confronted my Supervisor in Houston back then, complaining about our activity. "Research is my responsibility. You're out of line here." My Supervisor had said to him, "Well, Sir, you have set up a system which cripples your people so that they can't respond to requests from the operating divisions like this. We're going to do it here."

The Vice President was about three levels higher in the organization chart than my Supervisor, so that response took a lot of personal courage from him. Of course, the Vice President of Research would have complained about our activity to the Vice President of Exploration in Houston, to whom my Supervisor reported. That guy didn't know me, but he did know my Supervisor. He backed us up. Fortunately, we had tremendous success, both scientifically and in business terms. Otherwise, there would've been career repercussions for all of us! But we didn't learn about this at all until years later.

ZIERLER: I'm curious what you learned about the oil industry and how it changed over the course of your career, working for Amoco and BP.

THOMSEN: I can see that you did your homework, but we should put on the record here that BP bought Amoco, in 1999. I continued with the new company for another nine years. I enjoyed BP; I thought it was actually a better company than Amoco. How have things changed? Well, in one important way, a very visible way, almost all oil company research centers have been abolished. Basically, the only two I know of that remain are those of Exxon and Shell.

There have been many other changes, but let me just mention the changes that BP is going through. BP made a lot of investment in Russia. These have had some short-term payoff, but they've now been written off entirely, with the recent invasion by Russia of Ukraine. The world is going to have to learn to live without Russian oil. One of the ways we're going to learn to do that is by switching to renewables. BP has gone into that with both feet. About three years ago, they got a new CEO, who redirected the company. I think by 2040 or 2050, BP will not be producing any petroleum, only renewables.

We were ahead of the curve on this one. It actually started with a previous CEO, Lord John Browne. He was promoted to the House of Lords shortly after the Amoco acquisition, a recognition by the British government of the sort we don't have in America. When Lord Browne first bought Amoco, the new corporate name was BP-Amoco, which was changed to just BP a year or so later. By the way, "BP" is no longer an abbreviation for British Petroleum, it now stands for BP Corporation. They introduced, at the same time, a new logo, which is sort of a funky flower, and the slogan "Beyond Petroleum". In Lord Browne's day, they made tentative steps to get beyond petroleum, but now, BP is in it with both feet. I think they're setting the standard for the rest of the industry in the post-hydrocarbon economy.

ZIERLER: A very topical question. Given what's happening with regard to the crisis in Ukraine, what do you see as the overall ramifications to the oil industry as a result?

THOMSEN: That's really interesting, and I'm trying to get the National Academy to take up that question. You can imagine there's a lot of politics to that question. But in the short term, there's going to be a lot of suffering, especially by the Europeans, who are dependent on Russian oil. I think something like 50% of German energy comes from imported Russian oil and gas. If they just cut it off tomorrow, they will starve in the summer, and freeze in the winter. I think countries with a large exposure to Russian oil will seek to reduce their dependence, but that will impact their economies, and they will try to replace it with other sources.

What are the other sources? Conservation, that's the easy one, but it's so easy that I think people have already done a lot of that. The next thing is renewables, but that takes time, and investment, and effort. The next thing is replacement hydrocarbons. Where could they get the hydrocarbons that they're no longer importing from Russia? Some of the shortfall can be made up by imports from the Middle East (who are not particularly eager to help), and some from the United States.

You might know that the United States is now the world's largest producer of hydrocarbon energy. We can eventually export more than Russia did. But it takes a while to produce more. You have to explore and drill wells, and build infrastructure. Fortunately, we have a lot of production that's shut in because of the low price of oil just a few months ago, and we can increase our production by a few percent fairly quickly. But to make up for the massive shortfall caused by not using Russian oil will take a while.

I think it's going to mean a lot of disappointment for a lot of people who were counting on Joe Biden to reduce the use of hydrocarbons, because the demands for national security are going to trump the demands for reducing global warming in the short term. In the long term, it'll have to mean major increase in use of renewables: wind and solar and nuclear.

ZIERLER: When you retired in 2008, what did you want to pursue? Was it full-time work, or did you want to do more consulting?

THOMSEN: The day after I retired, I was recruited by the University of Houston to join their faculty. I asked, "How much teaching would be required?" They said, "Whatever you want." I said, "I'll do it with one condition, that you should not pay me any money at all." Because if they pay you, they can tell you what to do. I was financially secure and didn't need the money, but I did need the freedom. And I have been able to pursue research in exploration geophysics at the University of Houston, despite not having the resources of a large company behind me, nor a large grant from the National Science Foundation. I found that all it takes is a personal computer, access to the scientific lecture, and the willingness to re-examine old assumptions. Of course, all science is predicated on some sort of approximations to the most fundamental laws of the universe that we know, and that's especially true for applied science, so we make approximations.

And often, the approximations are required by the externalities of the situation, for example, by the cost-benefit tradeoff, or the availability of high-speed computers. Many externalities have driven our adoption of approximations. Let's be generous here and assume those decisions were correct at the time they were made. But we normally stick with them a lot longer than we should. I've been looking at some of these things, and for example, my latest work is revising some fundamental understanding of rock physics, going back 70 years. Two-thirds of a century, we've all believed this, but it's theoretically wrong. And it's easy to show that. However, there's been a lot of resistance to these ideas.

For example, that manuscript has been rejected by both of the major journals in exploration geophysics. But afterwards, it was voted Best Paper at the convention. I think it's going to eventually be seen that the original derivation of this fundamental idea was simply wrong, and that it might only be valid in some approximate sense. But we're going to have to do a lot of experiments to determine the accuracy of that approximation. To me, it's been a very satisfying post-retirement because I have been able to make these fundamental advances, despite my ongoing responsibility and obligation to protect BP's proprietary secrets and despite my having such limited resources.

ZIERLER: Given all of the academic freedom you had upon retirement, did you find you were picking up questions you had left back in your academic life? Or were these questions that specifically were influenced by your work in private industry up until the point you retired?

THOMSEN: It was the latter. Things I didn't do at Amoco and BP. I was sort of aware of those things, but I couldn't see that they were going to be profitable to the company in the near term. When I was at Caltech, I had the idea that the only respectable occupation for a scientist was as a professor. But I came to understand that applied science could be just as interesting and challenging, even though it's actually useful to society. The profit motive simply adds a new dimension of challenge, and it also offers new opportunities. For example, in the exploration industry, we can do experiments which would be prohibitively expensive for any academic professor, because we hope to make money in the end from those experiments. We routinely do multi-million-dollar experiments, and we hope to find enough oil and gas out of them to more than pay for it.

ZIERLER: Tell me about some of your consulting work, starting with Delta Geophysics.

THOMSEN: We mostly give advice and instruction. I have heard that American companies spend each year, on continuing education of their own people, a sum which is comparable to the entire budgets of all the universities in the country. Put together all the industries, and imagine all their continuing education. That's comparable to the total of the budgets for all the universities in the country: The reason for that is that the expense of continuing education is very high. You've got to pay the employee-student salary, pay for his travel, pay the instructor, etc. Although continuing education is very expensive, companies (especially high-tech companies) are happy to do it because they depend for their profits on the technical skills of their people.

I've done a lot of that over the years for a long list of corporate clients, and for various societies. The premiere societies of exploration geophysics are the Society of Exploration Geophysicists, headquartered in Tulsa, of which I was president in 2006 and 2007. Then, there's the European equivalent. I've taught a lot for those. They canvas their members for the course participants, normally employees of oil companies.

ZIERLER: What was the point of connection that got you involved with Berkeley Lab?

THOMSEN: The main point of connection is that we own a summer place in Northern California. Of course, you know that the San Francisco Bay Area is not in Northern California, it's in Central California. Our place is in Northern California, three hours north of the Bay, but we fly through SFO. I visit LBL whenever I can, and at one point, they said, "Why don't you join us as a Visiting Scientist and come when you can?" I regard LBL as my scientific home when I'm in California.

ZIERLER: What are some of the facilities or collaborations that allow you to advance your work at Berkeley Lab?

THOMSEN: Oh, the people are great. It's really an outstanding research environment. They're typically focused, more than a university is, on applied science. They have a department of Earth and Environmental Sciences, and they are interested in all sorts of things I'm interested in. For example, fracking, carbon sequestration, hydrogeology. Many things like that they pursue, which have implications for national security or national economics. I've found very useful collaborations with a number of those people.

ZIERLER: Let's go back and develop the narrative for your education. To go back to when you were an undergraduate at Caltech, how much time did you spend at the Seismo Lab?

THOMSEN: I was lucky to have a summer job at the Seismo Lab when I was a sophomore. At that time, the director was Frank Press, and I worked directly for him. He had a research project to understand the Central Valley of California. Just looking at the map, you can see it's an unusual feature. He was interested in it, to understand the tectonic reasons for the creation of that large basin in the middle of California.

As an undergraduate, of course, I had very few skills to help with that. But Caltech was quite enlightened, and they paid me a summer salary to learn how to program a computer. It took me half of the summer to learn enough to program a solution for a set of equations, which Dr. Press had posed to me. Of course it was an inefficient use of NSF money. If Press had just wanted to solve the problem, he could've solved it a lot cheaper by hiring somebody who knew how to do it. But part of the rationale for these things was to support education. With the knowledge and consent of the NSF, he hired undergraduate students who didn't know anything, and taught them geophysics and some computational skills, which eventually maybe solved a small part of the problem.

ZIERLER: What was Frank Press like as a person? Could you interact with him? Was he approachable?

THOMSEN: He was a bit intimidating for me. He was, of course, a Very Important Person, and became even more important after he left Caltech. But he was a buttoned-down guy, and I was not. I would say that the best description I can give you of those days is that he left me alone, and he allowed me to make my own progress. I rode a bicycle every day from an apartment near campus. You understand that in those days, the Seismo Lab was in a mansion in the hills above the Rose Bowl. That was an amazing experience because we were away from the campus, with some of the best seismologists in the world sharing office space in the various bedrooms of the mansion.

ZIERLER: So I understand, was there a dissatisfaction with physics that compelled you into geology and geophysics, or was it really this summer experience that got you involved in the field?

THOMSEN: I would say my reasons were inadequate. I made that decision based on reasoning of the sort that a 19-year-old makes. It's amazing how 19-year-olds are called on to make life-forming decisions when they're really not competent to do that. Yet, I happened to make that one in a way which I've never regretted. Part of the reason, I think, was my academic advisor, Clarence Allen, whom I admired a lot. He just died last year. He was a remarkable guy, who was elected to the National Academy of Engineering after I left Caltech. I thought back then, "Maybe I could be like him." It really is an insubstantial line of reasoning, but when I look back on it, that was basically my reason.

ZIERLER: To the extent you were aware of the things that were happening among the faculty, grad students, and post-docs, what were the big issues during your time at the Seismo Lab as an undergraduate? What were people working on? What were some of the debates in the field?

THOMSEN: This was before plate tectonics, so we were interested in the composition and structure of the deep interior of the earth, classical seismology I would say. I think nobody then really predicted the explosion of ideas that would come just a few years later. I think we all thought it was business as usual, we were getting better data and learning more about the earth, but I would say that nobody really understood just how things would change in the next decade or so.

When I first got to Columbia, the first week I was there, Professor Maurice Ewing invited all of us incoming grad students to a welcoming dinner at Lamont Observatory. He congratulated us all on our good timing, saying "The next decade will be a golden decade of discoveries about the earth." We did not appreciate it at the time, but he was exactly right. During my time at Columbia, plate tectonics happened. When I got back to Caltech in 1970, the basic ideas of plate tectonics had been well-established and accepted, and we were mopping up details.

ZIERLER: How did the Seismo Lab and your interactions with professors influence your choice of graduate school?

THOMSEN: Frank Press said, "You're interested in rock properties; go to Columbia. They have some good rock-squeezers there." I didn't realize at the time, but Press had done a PhD at Columbia under Professor Ewing, before coming to Caltech. I didn't realize he was sending me back to his alma mater. My grades were not so hot at Caltech. I was above average, but not in the top percentile of students at Caltech. But I think that Press intervened with the Admissions Department at Columbia, which I appreciate.

ZIERLER: Was the plan to pursue geophysics and seismology? How did you get involved in mineral physics specifically?

THOMSEN: That's an interesting question. I went to Columbia because they had a program which embraced both geophysics and space physics. I thought I would probably go into space physics when I got there; my first advisor was Robert Jastrow, who was famous in space physics.

But as I was trying to learn about the origin of the earth, I encountered some questions about mineral physics. I took a course in high-pressure mineral physics, and that led to changing my thesis direction away from space physics. I left Jastrow and joined the group of Orson Anderson. There, I did a thesis in mineral physics, of which I was quite proud at the time. But history has shown that it was a dead end. It never led to anything of importance. I would say, frankly, that most PhD theses are like that, of ephemeral interest. Only the rare PhD thesis turns out to be fundamental, answering or opening major questions.

ZIERLER: Tell me about returning to Caltech and the Seismo Lab for your post-doc?

THOMSEN: I left France, where I had a permanent job at the Centre Nationale de la Recherche Scientifique. I was a Fonctionaire in the French system. I had lifetime job security there, but I left for a two-year contract at Caltech. In France, I was in a high-pressure laboratory, surrounded by solid-state physicists. I wanted to get back to geophysics, so I did that.

It was wonderful. I got to know the geophysics faculty at the Seismo Lab a lot better as a post-doc than I had as an undergraduate, for obvious reasons. We had a lot of luminaries: Charles Richter, Hewitt Dix, Hugo Benioff. The director was Don Anderson, much younger than these. Don died a few years ago, diagnosed with terminal cancer when he had a year to live. He spent that year in the most remarkable way. He organized many of his colleagues to write joint papers with him. All those were collected and published in a memorial volume shortly after he died, in December of 2014. I was pleased to be one of those. When a guy like Anderson says, "Will you help me in my last year?" you've got to say YES. There's no way to say NO.

We did that work together, work of which I'm quite proud. Basically, that paper was applications of seismic anisotropy to global geophysics. It's my perception that in the academic world, the understanding of seismic anisotropy is much more primitive than it is in the applied world. Maybe that's because of the type of data we have to work with. That paper was an attempt to bring ideas of anisotropy to the global seismic community.

However, I don't really think it was a successful attempt. Most papers only get a few citations; I don't know how many citations that one's got. But by contrast, the paper I wrote in applied geophysics, my first paper on anisotropy, is the most frequently cited paper in the history of the journal of GEOPHYSICS, over 4,000 citations. If you Google the phrase "Thomsen parameter", you'll get back hundreds of thousands of hits, which is kind of surprising because there are not hundreds of thousands of geophysicists in the world.

ZIERLER: What was so significant about this work? Why did it gain such traction?

THOMSEN: It made the study of anisotropy feasible. It introduced a crucial approximation. That approximation, basically a linearization, was taught to me by Gerry Wasserburg at Caltech when I was, I think, a junior. I took a course in mineral physics from him. He said that exactness is overrated, and many times, a linear approximation can be more useful. I remembered that, and I applied it once I got to Amoco. It turned out to be exceedingly useful. Anisotropy is fairly complicated algebraically. You have to find approximations to make it feasible, and I found the appropriate approximation.

ZIERLER: When you returned to Caltech for the post-doc, how had the Seismo Lab changed?

THOMSEN: As I said, the director was Don Anderson, and they had an outstanding group of people. At that time, it was the worldwide focus of seismic research. Virtually every seismologist of any standing has rotated through the Seismo Lab, either for an afternoon, a few weeks, or a few months. Let me tell you another story from that time. I was reading the current literature, and I came across an article in the JGR citing an old result from Beno Gutenberg, one of the early directors of the Seismo Lab. I thought to myself, "That can't be right." I puzzled about it all afternoon, then it got to be evening, and everybody left. My wife was waiting for me back at home, but I just couldn't disengage. Finally, I had a flash; I thought, "I'll look up the original article by Gutenberg in the Seismo Lab library, and see what he really wrote."

However, in the library, that particular issue of JGR (from the 1950's) was missing. But I also found two leather-bound volumes called The Collected Works of Beno Gutenberg. I think these had been collected by the Seismo Lab from his personal copies of his papers, bound in leather, and given to him upon his retirement, then returned to the Lab upon his death by his widow. In the Collected Works, I found the paper I was looking for, and I found out that Gutenberg had been correctly quoted. But in the margin of the paper, opposite this conclusion, written in Gutenberg's own hand, was this phrase: "Das ist nicht richtig", This is not correct. He had changed his mind after publication! There I was, at the focus of seismic research worldwide, all alone, at nighttime, communing with the spirit of Beno Gutenberg! It was magical.

ZIERLER: What exactly was not correct? What did he miss?

THOMSEN: It was not central to his main conclusions. I don't remember the exact point, all I remember was the feeling of euphoria that swept over me. I rode my bicycle home through the dark streets of Pasadena without ever touching the ground.

ZIERLER: [Laugh] That's wonderful. In what way did the post-doc provide opportunities for you for what came after?

THOMSEN: It was a temporary job. I had to find a permanent job. I'm sure that my Caltech connections were helpful for me in finding a permanent job. One of the recent graduates was Francis Wu. Francis had joined the department at the State University of New York at Binghamton, and they were in a growth mode. They advertised a position as Assistant Professor, I applied, and was accepted. I'm sure that Francis' recommendation was crucial to that. I would say that Caltech was 100% responsible for my next job.

ZIERLER: For the last part of our talk, I'd like to ask some broadly retrospective questions about your career, then we'll end looking to the future. Between your undergraduate and post-doc, what are some of the ways you learned how to do science that have stayed with you ever since?

THOMSEN: Well, I have a fairly good mathematical background, and that, I learned at Caltech. But maybe here's an important piece of advice. I'll preface this story with telling you that my father used to say, "Leon, if it's worth doing, it's worth doing right." I took that as good fatherly advice to apply myself thoroughly to anything I do. But when you think about it, there are lots of situations where "good enough" is good enough, and you don't really have to do it perfectly well.

One of the faculty members at Caltech said to me, "If it's not worth doing, it's not worth doing well." That's the converse of my father's advice. It's more than a tautology, it's good advice: "Before you start on a project, think about whether, if you succeed, will it matter, will anybody care. Only if the answer to that question is a YES, should you try to do it well." Applying that idea to my later work at Amoco, I came across these very interesting ideas about anisotropy, and I did ask myself the question, "If I learn about this stuff, will anybody care?" I decided, "Maybe, so let's take another step in that direction." One step after another progressively confirmed that it was important and worth learning. I would say that process, I learned at Caltech.

ZIERLER: In what ways were you able to apply your academic skillset in private industry? What are some of the big lessons to be learned from your career?

THOMSEN: Well, that's one of them. The other one I've already mentioned is to examine assumptions. We all make assumptions and approximations, but we don't often examine them carefully. We should do this, and do it consciously. I can think of many instances in my industrial career when we could have had an idea much earlier than we did, but we ignored that idea, although we were so close, because we didn't examine our assumptions. As an example, I did not invent fracking. A guy named George Mitchell invented fracking in the early part of the 21st century. But I could've invented it years previously, because I was interested in natural fractures. It would've taken only a small step for me to think, "We can make our own fractures." In fact, the industry had been doing that for decades, making fractures in deep formations to improve the permeability and the flow of oil to the well bore. But Mitchell applied the same ideas much shallower in the crust, and more intensively, to shale formations.

I could have had that idea. But I didn't. In my defense, nobody else did either in all those years. And that idea has been revolutionary, reversing the decline of American production of oil, in decline since 1971. King Hubbert was a geophysicist for Shell, Stanford, and the USGS. He predicted, I think in the 1960's, that American production of oil would peak in the 1971. It peaked in exactly the year he predicted, despite the evident shortcomings in his theory. The projected decline of production following "Hubbert's Peak" dominated my thinking for years and years. I always thought it was the job of high-tech geophysicists like me to find the ideas, the technology, to discover the oil to postpone the arrival of the end of the era of oil as long as possible. In my generation, geophysicists learned amazing new technology, both on the academic and the industrial sides. But on the industrial side, we didn't find a lot of oil. We only increased the world's endowment of oil by something like 20%.

But late in my career, guys like George Mitchell discovered enormous amounts of oil locked up in shales. All it needed was the invention of fracking to get it out. That invention has revolutionized the course of the hydrocarbon economy. It's postponed for many decades the time at which we'll run out of oil. On the negative side, it has increased the problem of global warming. That's an existential threat, of course, to the whole world. So we're going to have to learn how to deal with that. But when you think about how our standard of living has improved over the last century, due to the availability of cheap oil, that's also been a fundamental aspect of human existence. That era is now coming to a close, and we're approaching a new time when we have to deal with the consequences of the hydrocarbon era. But with people like the alumni and the faculty at Caltech, I think that society will find the technical parts of the solution to that problem.

ZIERLER: Between the basic science and the applications, what are you most proud of over the course of your career?

THOMSEN: I think I'm most proud of the fact that some of my contributions have been very impactful. I would not say they were very profound, or complicated, or that nobody else could have done that. I think that if I hadn't done it, somebody else would've done it, sooner or later. What I'm most proud of is that my contributions have been so heavily used. They have had a discernible effect on the oil industry, and through that on the world economy. And I find it quite humbling to think that a guy sitting at a desk, scribbling equations on a pad of paper can be ultimately responsible for this tremendous activity.

ZIERLER: Last question, looking to the future. For younger people in the field who are interested in geophysics and even pursuing a career in industry, would you say that fossil fuels is still a viable and exciting field to go into? Or are there opportunities in geophysics for new fields in renewable energies?

THOMSEN: I think both are true, so my advice to students would be to prepare yourself broadly, so that you can change focus as your career goes on, if necessary. A student graduating today will have a professional career spanning 40 or 50 years, and he can expect that there will be major changes in the world ,and in whatever professional pursuit he follows. He (or she) should be prepared, intellectually and emotionally, for those changes.

ZIERLER: Leon, it's been a great pleasure spending this time with you. You've provided such great insight into the Seismo Lab and in your career. I'd like to thank you so much.

THOMSEN: My pleasure.