Paul Richards (PhD '70), Geophysicist

Two major issues that have animated Paul Richards's career are wave propagation in the Earth's interior and monitoring underground nuclear explosions. Prior to his graduate work at Caltech, Richards focused exclusively on pure math at Cambridge. His thesis was a theoretical analysis of wave propagation; since then, he has moved increasingly to the observational side of the field, because that is where he saw the most opportunity. Among his more prominent discoveries, with Xiaodong Song, was the observation that the Earth's inner-core rotates faster than the planet as a whole, which has major implications for our understanding of Earth's magnetic field, its evolution, and the way it transfers heat.

In the field of nuclear security, Richards has been a visiting scholar at the US Arms Control and Disarmament Agency and has served in an advisory role at the Comprehensive Test Ban Treaty negotiations. At Columbia, he has taught a popular class on weapons of mass destruction, a topic that greatly concerns him. Richards is the recipient of numerous honors, including Guggenheim and MacArthur Fellowships, and the Seismological Society of America's 2009 medal for outstanding contributions in seismology.   He was elected to the National Academy of Sciences in 1985.

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Thursday, April 14, 2022. I am delighted to be here with Professor Paul Richards. Paul, it's very good to be with you. Thank you for joining me today.

PAUL RICHARDS: Hello, David. Thanks for the invitation.

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

RICHARDS: My full title is the Mellon Professor of the Natural Sciences, emeritus, at Columbia University. I gave up my full-time job in 2008 and became emeritus. From time to time, if I still need a formal appointment, I'm given the title of Special Research Scientist, which is a temporary job, and I pay myself, if I raise funds, through Columbia, as the principal investigator of a specific project.

ZIERLER: Tell me about the history of geophysics and seismology at Columbia. How far back does that go?

RICHARDS: It really goes to 1949, when the Columbia Department of Geological Sciences had a very ambitious member, Professor Maurice Ewing, who had made a name for himself in the second World War for his study of the oceans and the deep understanding of aspects of the ocean that were important for the US Navy. He could not build seismometers in Manhattan because it was too noisy. At the time, a man called Dwight Eisenhower was the president of Columbia, and he had the problem that Maurice Ewing was threatening to leave and accept an invitation to lead a new department at MIT. MIT was going to give him a country estate, where he could do the work of building seismometers in a quiet environment. Eisenhower said, "Hey, we can do that…" and offered a suburban property, which had been given to Columbia, as part of the estate of Thomas W. Lamont (who had long worked in finance with J.P. Morgan).

So in 1949, Maurice Ewing initiated a new observatory, as it was then called --- the Lamont Geological Observatory. It included extensive efforts to study the world's oceans, as well as the work of designing and building seismometers --- which was done successfully with his first graduate student, a guy called Frank Press, who subsequently became the director of the Caltech Seismological Laboratory, and who left Caltech in 1965 to head the Department of Earth Sciences at MIT, then went onto fame and fortune as Jimmy Carter's Science Advisor and served two terms as president of the US National Academy of Sciences. All of this sprang from Frank Press's early role as Maurice Ewing's graduate student building seismometers. And they built what is still today called the Press-Ewing seismometer, which was technically a great advance because it enabled measurements of what we called long-period seismic waves, which provide information on the deep structure of the earth; and they were deployed at a small number of sites in the 1950s around the world, so successfully that they then became the backbone of a larger global deployment in 1962 and '63, known as the World-Wide Standardized Seismographic Network.

All of that work sprang from Maurice Ewing, who went on to make discoveries that the oceans were utterly different from the continents. They had a very thin crust. Maurice Ewing was just a powerhouse. He led so many new projects. In answer to your question, the key individual was Maurice Ewing, the founding director of what became the Lamont-Doherty Geological Observatory. It was changed more generally to be the Lamont-Doherty Earth Observatory, as we know it today. But the tradition has always included a program in the oceans, and it's a place that has the reputation not so much for theory, but for the practical matter of building huge databases so that when theories came along, like the theory of plate tectonics, they could quickly be evaluated and thoroughly analyzed; and the ramifications of that theory made practical because of the datasets that we had at Lamont, built up over decades by Ewing and others.

ZIERLER: Institutionally, I'm curious if the Seismo Lab at Caltech and the endeavor at Columbia worked in tandem, sort of as an East Coast, West Coast team in geophysics and seismology.

RICHARDS: They certainly influenced each other, but I would say that part of the overall process, perhaps even more important than collaboration, was the sense of competition. I went to Caltech the semester immediately after the departure of Frank Press to MIT in 1965, and very definitely, the people who succeeded Frank Press, in the best way, competed with other leading academic institutions. Collaboration wasn't so much the driver. [Laugh] Collaboration came later on really big projects, where everybody had to work together to build the IRIS Consortium and things like that to improve upon the global network of seismographic stations. The worldwide system I briefly described to you was old-fashioned analog recording, photographic plates with wiggly lines written on the paper, so there was the need for everybody to collaborate to move into the digital era. But on the scientific side of making discoveries about the Earth, I think it's still true that there's more of a sense of competition that prevails than collaboration.

Opportunity in Observation

ZIERLER: Some overall questions about your research career. First, are you more on the theoretical or observational side?

RICHARDS: I started out as totally in theory. But over a pretty long career, more than 50 years at Columbia, I have moved much more towards the practical observation side. But my institution did that to me, and I was happy to make the change because theory is usually best left to young people, and I'm not in that category any longer.

ZIERLER: What does that say more broadly about the field, in terms of your switch into observational work?

RICHARDS: I think one is opportunistic. You see opportunities, you see things that you could do that other people don't appear to be doing yet, and you carve out a niche for yourself. For most of my career, I worked as a theoretician. But then, certain observations, sometimes which we couldn't develop a theory for, but we could analyze in empirical ways, for example, to locate earthquakes much more accurately than had been done hitherto. That became a very practical issue, and that's what I've done for the last 20 years.

ZIERLER: What have been some of the most important observational theories in your career, things that have served as a guidepost in interpreting the data?

RICHARDS: Seismology isn't organized very well. There are about 20 different specialties. I think it's fair to say that most of us know about a handful of these specialties, but it takes quite a while to get an overall perspective on the majority of them. I think over the years, when Frank Press and Maurice Ewing were active, there was always the need to make measurements at longer and longer period to study the Earth's normal modes, which was a great discovery of the 1960s. Conceptually the whole Earth can resonate like a bell, and the challenge then was to make observations of those frequencies. That was a collaborative project, and measurement of those frequencies and their interpretation improved our knowledge of the Earth's interior, averaged over depth ranges of a few-hundred kilometers. But as time goes on, you want more and more detail about the Earth's internal structure, and in order to get that knowledge, there's a tendency to work with shorter and shorter periods because they're more sensitive to some of the details.

The pendulum swings. Some decades, it's more important to improve our understanding of observations and how to interpret them at the longer period. My own opinion currently is that we've done that pretty well for quite a while, and now we're tending to see more interest in observations made at shorter period to get more specific detail. But you asked about what things I've been involved with. I had a great excitement in the 1990s when working with a post-doc at Lamont, Xiaodong Song, who did his Ph. D. work at Caltech. We discovered seismological evidence that the Earth's inner core, right at the center of the Earth — it's about the size of our moon — is slowly moving relative to the mantle and the crust at rates that we can perceive in a human lifetime. It's a solid inner core of the Earth surrounded by a fluid outer core. The concept that there's an entity right at the heart of our planet, which is associated with the way our magnetic field is generated, kind of caught the public imagination, to think that there's an object inside the Earth that is moving on a time scale that can be elucidated. As a piece of research, that was, I would say, a discovery. The evidence for it, came from study of short-period seismic waves, and it's still an intently-pursued subject today, as we continue to nail down some of the details.

ZIERLER: What have been some of the main research questions that have driven your interest in seismology and geophysics over the years?

RICHARDS: They've changed at different times. There's another whole aspect of seismology that I started out with, which I found interesting. What is happening at the earthquake source when stresses have risen to a level that, suddenly, one day, there's a great fracture, and motions initiate on a fault plane because it's not strong enough to withstand the building stresses, and rock literally breaks on a plane of weakness? On a very short time scale, rock slides past adjacent rocks on a fault plane, stress is relieved, and a spontaneous set of motions begins. What is the aspect of fracture mechanics that puts any constraint on the motions right at the source of an earthquake, and what is the underlying physics associated with fracture on such a massive scale, as we sometimes see? That's one aspect of seismology. Some people study waves as they propagate and learn about the waves as they pass through and we learn about Earth structure. Then, others are more interested in the physics of earthquakes; and the underlying largest of all questions there, is to ask if this a phenomenon that, one day, we can hope to be able to predict in some way? Those are kind of the big-issue things that separate people who study Earth structure from people who study the fundamental processes of material failure that take place when an earthquake occurs.

Then, another whole class of things has to do with explosions. Seismology was a very sleepy little science, really, not much money spent on it, until suddenly, in the early 1960s, when nuclear test explosions were no longer allowed in the atmosphere because of the associated radiation hazards and problems of nuclear fallout. A treaty of 1963 banned nuclear explosions in the atmosphere, and nuclear testing went underground. Suddenly, seismology was flooded with millions and millions of new dollars per year in the effort to do two things. One, to have the capability to monitor the nuclear weapons development of a potential adversary — what was Russia doing, what was China up to? — and the other was to support a major initiative in nuclear arms control. The Limited Test Ban Treaty was very much promoted at Caltech by Linus Pauling, who got the Nobel Peace Prize for his leadership in achieving it. I never met him, but I met his daughter Linda and his son-in-law, Barclay Kamb, who was a provost at Caltech and a faculty member. I came to know him very well over the years.

That whole effort to turn the Limited Nuclear Test Ban Treaty, negotiated very quickly in 1963 and signed and ratified by a number of countries around the world under the leadership of Kennedy in the United States and Khrushchev in the Soviet Union, did not provide a total ban on nuclear testing, but if seismology could be improved enough to enable monitoring the only environment in which nuclear test explosions were still allowed — this would largely be an exercise in seismology — then that Limited Nuclear Test Ban Treaty could be replaced by a comprehensive ban on nuclear weapons testing. Since you asked about the things that kind of guided my own career, more than anything, I think it was that one. Working towards the objective of improving the monitoring capability, even for nuclear test explosions conducted underground. It's a long story, but after 40 years of effort, the text of that comprehensive treaty was finalized in 1996. It's been signed by over 190 countries, and various monitoring technologies are brought together as part of the effort to ensure compliance. It's still not a treaty that's formally in effect for a number of political reasons. But at the technical level, we monitor compliance with that treaty extremely well. The goal of being able to monitor even the underground environment, even down to very, very, very small test explosions: more than anything, has been one of the things that's guided the type of work to which I was attracted.

ZIERLER: Of course, over the course of your career, computational power has increased significantly. How has that been relevant for your work?

RICHARDS: Not very much. I'm not a very good programmer. When I was at Caltech, I was proud of programs I wrote that built on a theory for how waves propagate. As for being able to compute what seismograms should look like and to match what we actually observed: I did some of that. But other people are much better at that than I ever was. Still, today, I'm glad to have colleagues who do that work, but it's not work that I lead very much. I wrote a thesis at Caltech about the theory of wave propagation, and I did write programs, but they were always too complicated, and they never really took off because I was never really good at writing programs. [Laugh]

ZIERLER: The decentralization of data that exists nowadays in seismology, where it's not centrally archived on an institutional basis, what has that meant for you?

RICHARDS: It's just an enormous change. A few minutes ago, I was telling you about the degree of fundamental competition between MIT, Berkeley, University of California at San Diego, Caltech, a handful of other institutions. But it became apparent that the whole way in which seismometers were operated and wrote records of the ground motion at each instrument had to be radically changed, to bring us into the digital era — because with digital data, so much more sophisticated processing could be done. Over a period of about 10 or 15 years, it became apparent that a whole new structure was needed within the academic profession of seismology to replace the ad hoc system of government agencies doing some of the work and other agencies doing different types of work, and none of them doing the type of work on a scale that would match what could be done if you really organized things well.

Gradually, instead of the US Geological Survey taking the totally dominant leadership role, which had been the case for 10 or 15 years, a group of academic institutions developed in the early 1980s. It included Don Anderson, and Freeman Gilbert at the University of California in San Diego, and probably the most important of all of the leaders in this matter from academia was Adam Dziewonski from Harvard, who had a small group of fantastically good students who developed clever ways to acquire the data and circulate it. The great majority of US grad schools with programs in geophysics came together in the mid-1980s, specifically 1984, and organized as the Incorporated Research Institutions in Seismology, which was a consortium. It worked with the US Geological Survey in several ways, and has provided the leadership role over the last nearly 40 years of building the type of Global Seismographic Network needed for long-term research purposes, as well as providing all sorts of instruments for people who mount ambitious temporary deployments to study specific research issues. The IRIS Consortium made it important for different campuses to collaborate, and Don Anderson at Caltech played a lead role. The three leaders now, they've all died, each had their separate roles. They had spent decades competing with each other, but they came together very productively in the early 1980s to set up the IRIS Consortium.

ZIERLER: Have the theories changed as a result of all of the new data? In other words, what was considered accepted science when you were a graduate student that might not be so certain these days?

RICHARDS: There were a number of very important aspects of the theory of plate tectonics that required observational confirmation and fine-tuning. A lot of that work went on. More than fine-tuning, the basic confirmation of the central ideas of plate tectonics was largely done by careful studies of the data acquired from the World-Wide Standardized Seismographic Network put in place in the 1960s, using analog recording. A lot of that good work was done at Lamont, and some of it was done in San Diego. To understand what was going on to subducted plates, you had the whole concept of the new global tectonics, where a limited number of tectonic plates, on the order of about 20 of them, jostle together at the Earth's surface. They bump into each other, rub past each other, and spread apart from each other in the mid-ocean ridges. When they collide with each other, they can for example create the Himalayas. If one goes under the other, a subduction zone develops. It took a few decades to work out those details, and some of that working out is still going on. Which part of the Earth's surface is still deforming, which part is not deforming and stays rigid, we still are learning some of those details. But the big picture began to emerge in the 1960s and 1970s, largely from taking these theories and gradually working out the rates with which different parts of the Earth's surface were deforming. The challenge today includes understanding the geodynamics processes that drive tectonic plates, and that's a focus of research for geophysicists using data from the Global Seismographic Network.

Pure Math Before Caltech

ZIERLER: Let's establish some context. Prior to your arrival at the Seismo Lab, you were a mathematics major at Cambridge, not in geophysics or seismology.

RICHARDS: It wasn't just a major. I didn't do anything else. I went to an English high school, I was three years at Cambridge, the typical bachelor's program. I never went to any class other than a class in mathematics. I never had to write an essay, I never had to go to a laboratory, I didn't do any research. You simply went to lectures, and you were examined by how well you could solve problems in a few three-hour exam sessions conducted on an annual basis. I didn't do any chemistry. If I did any physics, it was only to take mathematics classes on theories of classical mechanics, electricity and magnetism, and quantum mechanics. When I was looking for what I would do next, I had been in mathematics up to the age I then was, about 20 or 21, and I never really thought about it. I could do mathematics fairly easily, everyone else in my family did mathematics.

ZIERLER: Was it applied or pure mathematics you did?

RICHARDS: Pure mathematics. It included rigorous understanding of what integration and differentiation meant. You didn't work with theories unless you could understand their formal basis. It was very much pure mathematics. I stumbled into Caltech just by chance. That's another story. But when I arrived, I knew almost nothing about geology or the Earth's interior. But it didn't take long to find out that the Earth does have a core, two of them, an inner and an outer one. And it was all just wonderful news to me. I didn't know anything about geology, and I was promptly put in the Geology 101 class taught by the chair of Caltech's Geological and Planetary Sciences, Bob Sharp, and I loved it. But it was all new to me.

ZIERLER: Of all majors, mathematics, of all places, Cambridge. How did you find yourself at Caltech in the Seismo Lab?

RICHARDS: It was just chance. I didn't even think about applying to graduate school, as one did in England, until toward the end of what you'd call one's senior year — although in England, that would be the third year of the undergraduate program. I didn't even start to think of it until about March or April, with only two months left as an undergraduate. I had two brilliant older brothers who aced every program they ever got into in England, and I had to do something different. I decided to try to get into an American graduate school. I wrote away for application to Harvard, Cornell, and a couple of other places, and they all wrote back saying, "You're too late. Send us $25, and we'll give you the forms for next year." Caltech wrote back and said, "You're too late, but here are the forms anyway. Maybe we'll read what you send us." It was just complete chance. I filled in the paperwork to do elementary particle physics at Caltech, and in the summer, to my surprise, I got a letter from the Geological Sciences Division saying, "We note your application to do graduate work in physics. It would be good to have people with mathematical knowledge working in the geological sciences. If you wish, without prejudice to your application in physics, we'll be happy to use your paperwork as if you had applied in geological sciences." I thought about that. I loved hiking in the mountains and all sorts of things, so I wrote back and said, "Yeah, sure, I'd love to do that."

ZIERLER: Were you aware of Feynman and Gell-Mann? Was there an allure to particle physics?

RICHARDS: I knew the names of the Nobel Prize-winning physicists at Caltech, yes. But then, the Physics Department sent me a letter saying, "Sorry, we don't have room for you in the Physics Department." Then, I got a letter from the Geological Sciences Department saying, "Yes, you're accepted."

ZIERLER: They made it easy for you. [Laugh]

RICHARDS: I said yes, and a month or two later, I was on my way to Pasadena.

ZIERLER: Do you know who on the faculty was driving this idea to recruit mathematically able students to the program?

RICHARDS: I don't know if Press was involved, but it would've been Don Anderson and Charles Archambeau, possibly Stewart Smith, three people whom I came to know really well. When I enrolled at Caltech, a new young professor had been appointed there, who became my thesis advisor. That was Jim Brune. But Jim showed up at Caltech at the same time I did, so he wasn't a key person making the decision to invite me. But in the end, he was perhaps my closest friend on the faculty. He started me out. He was a Quaker, he still is, and he's the person who formally married me at Caltech because he was Clerk of the local meeting on Orange Grove in Pasadena, where I was married in 1968. But the mathematical people, as I say, Archambeau, Stewart Smith, and Don Anderson. One of the things about the community at the Seismo Lab was that we didn't just work together, but we played together, too. That's to say we saw each other socially in the evenings, parties on the weekends. We would go off into somebody's cabin in the woods, we traveled around together, we enjoyed each other's company, not just during office hours, but to an extraordinary degree, saw a lot of each other each week. To a degree that I think was really quite unusual in graduate school.

ZIERLER: Just on a personal level, how daunting was it to enter the Seismo Lab without any formal training in the subject?

RICHARDS: Not at all. Because most of the good friends I made were all sweating it out with the hardest courses for them, which were the mathematics ones, which were easy for me. It doesn't take long to find out that there are a lot of different kinds of rock, and I was interested in that. I loved the basic geology classes. I didn't do very well in field mapping, but I enjoyed the experience of trying to learn it. The really hard things were the hard physics and mathematics courses that most students were required to take, which were just easy for me.

ZIERLER: How big was the incoming class when you arrived? How many students were in your cohort?

RICHARDS: This was a whole range of people doing geology and planetary sciences, but there were on the order of about eight of us. And I think we were pretty much all jammed into the same quite large room in the Seeley Mudd Building on the western end of the campus, as it then was, on the second floor, right opposite Bob Sharp's office, he being chair of the large GPS Division. He'd keep an eye on us, he'd wander in occasionally and ask how things were going. On his way to his own office, he'd go to the door across the corridor, wander in, keep an eye on us, and find out what we were doing. There was Sue Werner, who married and became Sue Werner Kieffer, John Davies, Dave Hill, Wayne Thatcher, Max Wyss; a year later, Tom Hanks came in. A year ahead of me, Bruce Julian, whose name you might remember from a paper that I sent you. He coordinated the writing, with contributions from several of us, trying to convey the ambience of the Seismo Lab. Also Torrence Johnson and Peter Lagus in Planetary Sciences. I'm going to guess on the order of 15 or 20, of whom maybe about 12 of us were seeing each other in the early courses we all had to take together.

ZIERLER: In the way that Feynman's reputation preceded him, did you appreciate in the Seismo Lab that the people who became your mentors were really giants in the field, even before you got there?

RICHARDS: Only a little. I came to know Feynman quite a bit because after one year, I took a job on campus of being a resident associate in one of the undergraduate houses. I lived as the resident associate on the campus in Dabney House, and because Feynman's lectures in physics were such a large part of the undergraduate community's hurdles in life, I saw a lot of him. He was a strong campus presence in his informal music-making. I participated in some of the undergraduate concerts, performing musicals in Beckman Auditorium. On those occasions, I would meet Feynman with his bongo drums. But were we intimidated? Not in the least bit, no.

ZIERLER: What were some of the great debates that were happening among faculty at the Seismo Lab when you were a graduate student?

RICHARDS: One of the things was plate tectonics. It turns out that the big ideas in plate tectonics had been around for quite a while, but they received an enormous boost in 1963, '64, '65 from Fred Vine and Drum Matthews at the University of Cambridge, who started to do careful analyses of the magnetic anomalies in the northeastern part of the Pacific Ocean offshore from the northwestern continental United States, the state of Washington and British Columbia, and started to see magnetic stripes in the mapped view of anomalies that could be measured from a ship. In about 1966, Fred Vine was scheduled to give a seminar at UCLA on the theory of plate tectonics, and Jim Brune organized a carpool to go and hear Fred Vine. This was one of the great ideas, which at least I think it's fair to say, to that date, had been left out of the curriculum of most American Earth Sciences graduate schools. The ideas of continental drift and so on had been around for quite a while, but this suddenly was applying modern analytical techniques to modern data coming from the oceans. Here was a man, Fred Vine, who presented the concept of spreading of seafloor that could be potentially dated by seeing what aspects of the paleomagnetic field had been frozen into the memory of rocks in the ocean floor as they spread away from seafloor spreading centers. It was such a simple idea. Fred Vine is a very good speaker, and he'd given that presentation probably ten times before, because it just took on like wildfire. A lot of people changed their careers in Earth Sciences departments at leading institutions across the United States to latch onto these ideas, the theory of plate tectonics. Here, for the first time, was a successful effort to demonstrate the truth of the underlying concepts. Caltech caught up pretty quickly, but it was all new to everybody at the time.

ZIERLER: Of course, when you were there, it was still in the mansion, separate from campus.

RICHARDS: Indeed. I took a lot of classes on the main Caltech campus. I had an apartment on 120 South Wilson Street for that first year. I would take classes on campus, then there was some kind of a shuttle bus arrangement. I can't remember the details of how I would get four or five miles to the west to go to the place where I was a graduate research assistant, and I was promptly assigned to a role supporting principal investigators, that would be Clarence Allen and Jim Brune, who, at the time, were doing seismicity surveys of the small earthquakes that occurred on a daily basis all over the state of California. I would typically take classes on the Caltech campus, then spend quite a few hours every week reading those paper seismograms and characterizing the number and location of the micro-seismicity, as we called it, all over the state. I had two different roles, learning the methods of doing research, and this was work which required Clarence Allen and Jim Brune to spend hours teaching me the details of how you read a seismogram; then following their instructions, carefully measuring, from paper seismograms of the old-fashioned type, details of the principal seismic waves; when they arrived, how big they were, and doing that at enough stations so that you could do the work of locating these events, in an effort to see if these tiny earthquakes bore any relationship to the really big fault systems, the San Andreas, the Garlock, and other faults.

And the short answer, at that time, was no. We had a network of about 10 or 12 stations that were moved, after several months of operation in one place, to another part of California. Whether we did a study of these small earthquakes very close to the San Andreas or far away from the San Andreas, we could see no pattern in the location of the micro-seismicity that, in that preliminary study, bore any relationship to the large-scale fault structures. A lot of that work was done prior to the Parkfield earthquake of 1966, which then nailed down the deep importance of the San Andreas as still a place for active earthquakes. But at least in the early survey studies we'd been doing, you couldn't really relate the micro-seismicity to the larger picture. Over a longer period of time, we got a better understanding of that. But at the early stage, it was an ideal project for just learning the basics of what an earthquake is, how to locate and characterize them, and that's what I've done ever since.

ZIERLER: What were some of the instruments at the Seismo Lab that might've served as a magnet for outside scholars?

RICHARDS: I knew that Hugo Benioff had died in his 60s, and had developed a Benioff seismometer that was widely copied and used at other institutions. Francis Lehner, who was the head of the Instrument Lab, an engineer, had responsibility for deploying instruments, some of which were sufficiently successful that they were applied elsewhere. Stewart Smith, a young professor when I was a student, developed the capability to use rods on the order of ten meters in length as what was called a strainmeter. You would anchor a ten-meter-long quartz rod at one end, and at the other end of the rod, you'd take it up to rock attached to the ground, and measure carefully the displacement between the end of that rod and the adjacent rock. And that became a very successful long-period strainmeter, which very excitingly, in 1960, was one of the three technologies that successfully documented the existence of normal modes of the earth. That was certainly a Caltech achievement that, for a number of years, was successfully emulated at other institutions. Not so much towards developments in instrumentation, but more towards gathering an overall understanding of the petrology of the mantle, the nature of these rocks that led to the features within the Earth's upper mantle that we inferred from the structure. We were informed by seismometers, and by interpreting the signals that they wrote, that certain steps in structure of the mantle at depth were related to the underlying petrology. The combination of seismology and petrology was great success, led by work of Don Anderson, and it really was quite influential. Not so much, to my knowledge at least, the instrumentation aspects.

ZIERLER: It's an embarrassment of riches, all the people to work with. What was the process like of determining who your thesis advisor would be?

RICHARDS: I think it was a toss of a coin. People would make a judgment before you even arrived on the campus who would take the responsibility for guiding you, what courses to sign up for, what research assistantship would occupy your time, what project you would contribute to. My initial guidance was from Jim Brune, who was absolutely brilliant in developing a basic physics understanding of the overall phenomena of earthquakes. He pointed me to a possible research project, which I pursued, which was the study of standard P-waves (the sound waves that travel through the Earth's upper layers), and how they interact with waves reflected from the Earth's fluid core — a wave that's reflected from great depth in the Earth. As one looks at earthquake signals recorded by seismometers, spread over greater and greater distance around the Earth's curved surface, the wave that goes through the Earth's mantle and the wave that's reflected from the Earth's core come together about a quarter of a way around the whole Earth. And these two waves start to interfere with each other. I studied that interference to see what information it conveyed, in the seismograms, about the structure of the base of the Earth's mantle, just above the fluid core. And very quickly, that analysis required a degree of sophistication in mathematical theory that meant that Jim probably wasn't going to be the right person to be the formal guide for my thesis research. The answer to your question is that, because I was heavily invested in the theory, the obvious correct person to be my formal advisor was changed to be Charles Archambeau, who was a wonderful, colorful individual with whom I got along very well. And indeed, I was able to defend a thesis in that type of work after about four and a half years.

ZIERLER: What was Archambeau like as a mentor? How often would you interact with him?

RICHARDS: Oh, daily, when he was in town. He would leave me alone, but if I had questions, I'd pursue him. I pursued him quite often, and he gave helpful advice. He was always supportive. Whatever idea I presented, he'd say, "Oh, that's wonderful," even if it wasn't. [Laugh] He was just a very friendly person. He died in 2020. I came to know him really quite well. He moved to Colorado after a while. Like me, he was strongly directed in his overall goals as a seismologist by trying to demonstrate — and he did it very successfully — the capability of seismology to provide the necessary technical support to progress in nuclear arms control. He provided important leadership after he'd left Caltech in the late 1980s, when Gorbachev, amazingly, emerged to lead his country, and in about 1987, for the first time, permitted foreign scientists to deploy seismometers on Soviet soil and allowed them to record the signals from Soviet underground nuclear explosions. It had been illegal for a seismogram of a Soviet nuclear test recorded on Soviet territory to leave the territory of the Soviet Union until Gorbachev agreed to the technical project that Archambeau led. Indeed, we found that the ability to interpret seismograms at relatively short distance from the Soviet main test sites allowed the work of monitoring to be done far better than if we'd just relied on teleseismic recordings (i.e., those at great distance). That was work that Archambeau very successfully led towards the grand objective of radically improving monitoring capabilities so that it could, if amenable in the political realm, provide the technical basis for achieving an objective in arms control. The political leadership, in the end, did not succeed. But the technical work was done.

ZIERLER: As you explained earlier, your work prior to coming to Columbia was much more theoretical. To what extent is that a function of simply the topic you were pursuing at the time?

RICHARDS: When I left Caltech, I took a post-doc for a year and a half at UC San Diego in La Jolla and carried on more with theory. But over time, especially when I was at Lamont, it was pretty clear that I'd have to get more practical than just doing theory. It just took a while to find the right students and to find a niche. You can't suddenly move into a field where you're competing with people who do very well anyway. You need to know enough about the subject to find a place where you can be productive. It takes a while to do that.

What Seismic Waves Tell Us

ZIERLER: What were the key conclusions of your thesis research?

RICHARDS: I showed that some of the most commonly observed seismic waves, as they traveled through the Earth, acquired certain observable aspects that conveyed information. For example, at the base of the Earth's mantle, right above the fluid core, did the mantle just go right down to the interface with the Earth's fluid core with no changes, all the way to the bottom? Or were there features at the base of the mantle whose properties could be studied from seeing their effects on seismic waves that just touched, in their ray path, the base of the mantle? To study the frequency-dependent characteristics of diffraction of seismic waves was the main feature. Then, I discovered a phenomenon of tunneling. As it's described in physics, it's the concept that waves can get through a barrier by tunneling through it without the energy needed to go over the top. There's a certain mathematical process by which mathematically, the waves of interest exponentially decay in certain directions, and if they meet the right conditions on the other side of the barrier, some of the energy can leak through the barrier and propagate successfully on the other side.

I showed that those properties, developed within the context of quantum mechanics, could be applied successfully to explain observable features of seismic waves. And this gave us information, again, about parts of the Earth's deepest interior. Another example: you would have a wave that would go downward nearly in a vertical direction through the mantle, go a long way down, but some little part of the energy would be reflected back up from a transition region in the mantle. Part of the energy would be reflected from the transition zone, but most of the energy would go straight down. To the extent that one could observe that weak reflection, what information did it give you about the transition zone itself? How thick was that transition zone? What percentage jump in properties from top to bottom could be estimated by processing the reflected signal correctly? Those are the kinds of things I was able to work on.

ZIERLER: How did these questions relate more broadly to what was happening in the Seismo Lab at the time?

RICHARDS: It was a small part of the overall activity. But a lot of the main activity was trying to get a better understanding of the fault systems to learn how old the faults were, if they'd been operating for 10 million years, 50 million years, 100 million years. Those were the large-scale issues at the intersection of geology and seismology. And Clarence Allen played a leading role in that perspective of seismological research. How is California put together? As the new ideas about plate tectonics began to emerge, it became apparent why different parts of California were of different age. How had they come together? What was the larger role played by the San Andreas in the big picture of plate tectonics? How did the interaction of the San Andreas fault in the northern part of the state, around Eureka and so on, then going out into the northeast corner of the Pacific Ocean and the northwest corner of the United States in the Cascade region, interact with the the rest of California? People were trying to understand the large-scale way in which the whole continent had been assembled. The discovery that truly gigantic, magnitude 9-class earthquakes must've occurred in the Cascades region, was made by several people — including a major contribution by Tom Heaton and Hiroo Kanamori at Caltech.

That didn't happen until long after I left the Caltech campus. But those were the kinds of issues that people were working towards, to try to understand how the whole Western United States was put together. How did structural geology convey information that could be brought to bear? Seismology is the study of how things are moving today, but to put it in the larger perspective, we must relate it to information coming from structural geology on what must've happened in the past — for example by going to certain fault structures today with massive amounts of land-moving equipment and building a big trench across a fault system in order to study the layering and how it has been re-arranged by past earthquakes. Kerry Sieh, when he was on the faculty at Caltech, working with others, tried to understand the evidence from damaged trees and trenching that enabled an understanding of the last few-thousand-years of plate motion from damaged structures on faults that could be, in a sense, exhumed, at least in their near-surface properties. A lot of completely different technologies and techniques were applied in seismology, some of them pertaining to study the last ten or more million years, some of them over the last few weeks, some of them over the last few centuries. A whole different range of time scales.

ZIERLER: What were some of the limitations, either in theory or instrumentation, that prevented your thesis from doing all that you might have hoped it would do?

RICHARDS: It worked out for me because I wrote a textbook after I got to Columbia, and I'm glad to say it's still in print. My thesis, essentially, was amplified and became one of the core chapters. The overall theory of how you come to an understanding of the propagation of seismic waves, which I began to develop in my thesis, became a backbone of about a third of the textbook I eventually wrote. The senior author, Kei Aki, wrote to me in 1975. I didn't know him well. He said, "Paul, I know of your reputation. I would be delighted if we might collaborate together on the writing of a textbook." It appeared in February of 1980 in two volumes, and from time to time, it has been updated. I was a young assistant professor when I started working for five years with him, from 1975 until it first appeared in 1980. To answer your question, then: that overall theoretical framework of seismology is still quite useful today because understanding tunneling and diffraction, which I tried to describe a few minutes ago, is an important part of learning how you extract information from the wiggles you see on a seismogram, and that came from my thesis work at Caltech, although it didn't really become a part of a larger structure of how to present it to a big audience until I worked with Aki to complete that textbook.

ZIERLER: While you were a graduate student, did the Seismo Lab feel like the center of the universe? In other words, if there was a larger seismology research community out there, did you feel part of that? Or was it not even necessary to consider life beyond Pasadena?

RICHARDS: For me, it wasn't important. I mentioned when we started out that the sense of competition that truly existed at the time – MIT was trying to build a good model of the Earth, Caltech was trying to build a good model of the Earth, people in San Diego and at Harvard were trying to do that. I didn't have any project that was at risk, shall I say, of a competitor succeeding. I could see my colleagues were trying all the time to be up-to-date on the latest wrinkles of someone else's model of Earth structure, but I wasn't in that game. I was trying to see how to come to an understanding of the way in which you get information from a seismogram in ways that weren't really threatened by what might be going on at other institutions. Later on, I got more competitive with other institutions, but when I was a graduate student, that didn't particularly bother me very much.

ZIERLER: Your subsequent work on the super rotation of the Earth's inner core, when did that start?

RICHARDS: In 1995. Maybe even earlier. About 1995, I presented a poster at the American Geophysical Union main annual meeting in San Francisco, using the idea that the surface of the Earth's inner core might have wrinkles on it. You faced the fundamental problem that the solid inner core is spherical. If something spherical is rotating, you can't really tell. You've got to find a marker. Then, I thought, "Maybe some parts of its surface are rough in ways that are different from other parts of its surface. If you look at a reflected wave, maybe over time, the reflection from a region at the surface of the inner core will be different at different times, if the thing is rotating." Didn't work. [Laugh] Then, one day, when I was writing a proposal to do a study of the possibility that inner-core rotation might be occurring, working with Xiaodong Song, who had recently gotten his PhD from Caltech working with Don Helmberger, it suddenly occurred to us that more successful would be not the wave reflected from the inner core, but the wave that went through it.

It was so exciting because the concept was, from Xiaodong's thesis, that the marker we would need to see if the thing was moving or not would be not any roughness of its surface, but deeply within its volume. The inner core had been discovered to have the attribute of anisotropy, which means that waves traveling through it traveled at different speeds in different directions. Anisotropic, means "not the same in different directions." If you looked at waves that went through the inner core, then it was like some glorified crystal, where it had different properties in different directions. As it slowly moved, the time it would take for a wave to go through it would be different at different times because the fast axis would've been re-oriented. From having that idea, to finding the evidence, then writing it up, doing the figures, and submitting it, took only three weeks. We submitted it to Nature, and that was absolutely the most exciting time in my own scientific career.

We were fortunate to work with a person whom I'd never met, a principal illustrator for Newsweek. People at Columbia University said, "This is really interesting stuff. Let's make sure that you have a good illustrator" and I was given a phone number. Just working with her on the phone, after about ten iterations, she generated what became the cover page of Nature for July 18, 1996, showing the Earth, the fluid core, and inside, the inner solid core, and the concept of it rotating with arrows around it. I thought it was a tremendous piece of technical art that helped us to tell the story. When Nature accepted it and it became published, I gave a press conference with Xiaodong in Manhattan, and the next day, we flew to an international meeting in Brisbane, Australia, and the news of our press conference was on the front page of the Australian newspapers. It doesn't usually happen in a person's career that you get that kind of global recognition. This somehow captured the public's imagination, or the people who write, such as yourself, the story of scientific discovery. It was on the front page briefly of the New York Times, until a TWA jet airliner crashed the same day and bumped us off the front page in the later editions.

ZIERLER: Given the significance of this work on the inner core, are there intellectual origins at the Seismo Lab? Was anybody working on the inner core when you were a graduate student?

RICHARDS: No. Not to my knowledge. The inner core was discovered in the 1930s by a remarkable woman, Inge Lehmann, from Denmark, who often used to come to Lamont to work in her later years. She was still writing good professional papers well into her 90s. I don't recall, at that time, at least, any work on the inner core at Caltech. I will go on to say that after our paper appeared, the general subject of evidence for inner core rotation — quite appropriately, because this is how science works — was deeply questioned. People wrote papers saying, basically, "The work of Song and Richards is garbage. Over the 28 years in which the earthquakes underlying their dataset occurred, the global network used to locate all those earthquakes has systematically changed from year to year. We don't believe the evidence for a travel-time change that must be due to inner core rotation. All that Song and Richards have done, is an artifact of mislocated earthquakes. Because the earthquakes were systematically mislocated in their work, they've wrongly interpreted the evidence for a slight travel time change.. Really, what's happened is, the earthquakes aren't where Song and Richards thought they were."

But this is the way science works. We had to go through a process — that took ten years — for a far, far better dataset to emerge. Namely, Mother Earth solved our problem by providing what we came to realize was much better evidence, derived from what we call repeating earthquakes. It turns out that many earthquakes repeat themselves at the same location, but years apart in time. If you take seismograms from a pair of such repeating earthquakes, you find that the pair of seismograms at each station all over the world look just the same — except that we were able to show there was a slight difference in the part of the seismogram for which the waves had traveled through the inner core. In 2005, we had a major paper in Science, which said that, by using repeat earthquakes, the original claim for evidence for inner core rotation was substantiated: and it's not due to some artifact of mislocated earthquakes. Because with repeating earthquakes, it doesn't really matter where they are. You can't mislocate earthquakes relative to each other when they write the same seismograms. They have to be in the same place. And if all the different wiggles look just the same, except the wiggle that corresponds to the wave that's gone through the inner core, then the inner core must've changed in some way.

Xiaodong Song is now a senior professor at Peking University, after a substantial career when he was a professor at the University of Illinois at Urbana-Champaign. He continues to do leading work, and it's still a very active area of research, because we face the fact that different lines of evidence for inner-core rotation from different datasets give a slightly different rate. Furthermore, the rate over decades may change with time. Sometimes the inner core rotates, sometimes it may rotate more slowly. John Vidale, a professor at USC, has presented what he regards as evidence that sometimes, it reverses and goes in the other direction. We still haven't got to the bottom of it. It's a very active research field. But the basic evidence that there's something worth studying here, that the inner core is not static and certainly sits within a vast outer fluid core, which has a viscosity pretty much like that of water. Here, we have a moon-sized object right at the center of our planet that's deeply involved in the processes that give us a magnetic field. And there's evidence that it's moving, as we would now see it today, from a perspective almost 30 years later, with a slightly unsteady motion. There's still work to do here to nail it. Maybe as it rotates, it's not rotating as a totally rigid object (it's almost melting all the way through its volume, so it may even be distorting). A lot of people are still trying to get the details. But the fact that something is changing down there on a time scale we can detect within a human lifetime — I think that has been firmly demonstrated.

ZIERLER: When you were a graduate student, was anybody talking about moving the Lab on campus? Or was that too far afield?

RICHARDS: I think that was far afield. That came later. It's always good to consolidate things. We didn't talk about some of the other activities. One of the key individuals at the old lab was Charles Richter, who I got to know.

ZIERLER: What was Richter like?

RICHARDS: He was obviously a world-class expert in his field. I think it's fair to say that he didn't follow modern research very much, but he was the guy to go to if you wanted the coordinates of a particular earthquake in California in the 1920s, 30s, or 40s. He had an encyclopedic memory of earthquakes, which sometimes got him into trouble because people would characterize him as a walking encyclopedia rather than a very careful scientist. He had a reputation for being very outspoken on a number of things, for example that only fools and charlatans make claims of earthquake prediction. [Laugh] But what I loved about him was his involvement, in that era, the 1960s, with the graduate students working at the old Seismo Lab as they participated in the ongoing process by which observatories all around the world reported boring details, about the times of arrival of various seismic waves at their observatories. Caltech had a number of seismographic stations in the Southern California network, and there was a full-time employee, a very careful analyst, who worked under the direction of Charles Richter, who worked at a third level down with the graduate student assigned that week to submit the weekly report on all the P-waves, S-waves, and other reflected waves from the Earth's deep interior that had been detected at different stations of the Southern California network.

Richter would occasionally come by, and he'd look at some seismogram that, for example, I might be analyzing, making measurements of the time of arrival of a certain wiggle. I can still remember, sometimes he'd look at it and immediately know where that earthquake was because he had a memory for how differently seismograms looked for different source regions around the world. At that time, when we would see a seismogram, there was no internet, no national or international basis for locating the source of that earthquake unless it had done damage to some particular town or something like that, and was in the news. If it was an earthquake way out there in the oceans or in some remote mountain range, we didn't know where it was until we'd interpreted the seismogram and found out the direction from which the waves came and how far away it must be. But when an expert such as Richter would look at it, he'd remember hundreds or thousands of seismograms he'd analyzed in the past, and he'd have a mental memory and think, "This one that Richards is looking at today is like one I remember from the 1940s." He'd know roughly where it was from. I'd be making my measurements at one part of the seismogram, and he'd say, "Oh, that's interesting. And did you look at this part of the seismogram?" and he'd point to a place much later in the same recording, at something I hadn't thought to look for. "There might be something interesting."

Then, he'd wander off. I'd find out he was usually right — there was another feature to be seen, which I hadn't appreciated until he pointed it out.

He was quite interested to see what the current generation of people was spending its time on. He was quite a character. His wife would pick him up in their car, and there'd always be a slight apprehension because there was a little worry about whether one's car would be bumped into by one of these two elderly drivers. [Laugh] I always appreciated the chance to meet him. He was in no way the research leader at the time I was a student. He had very, very, very few students himself over a long career, but he still had an important role as a careful analyst, and he wanted to make sure that the interpretation of seismograms at the most basic level of measuring things from them was done with care and attention to detail, and he did that very well.

ZIERLER: Reaching even further into Seismo Lab history, did you feel the influence of Benioff and Gutenberg?

RICHARDS: It was Benioff who did instrument design more and Gutenberg who did seismogram analysis more. The short answer is no. I think they were giants of their time, but the work had moved on. Longer-period instrumentation was in place, and more detailed studies of what we call surface waves and the dispersion that characterizes how they look on a seismogram had not been possible in their day because they didn't have the right instrumentation. I've become more interested, in my current research, in the writing of Gutenberg because when he came from Germany, he had become an expert in the way that the Earth's atmosphere carries infrasound, waves of pressure traveling as long-period sound in the atmosphere, which happens, for example, from nuclear test explosions conducted in the atmosphere. The waves spread through the air, but they're sufficiently strong that they can hit the ground near a seismometer and be recorded by the ground motion that the instrument is sensitive to. I'm currently working on a discovery we have from what Gutenberg initiated, concerning the first nuclear explosion ever, named TRINITY and conducted on July 16, 1945, in New Mexico. It generated seismic signals in Arizona recorded on an instrument designed by Benioff that Gutenberg analyzed, and today we're developing a new understanding of those signals. Here we are, 52 years since I left Caltech, where I'm suddenly very interested again in Gutenberg's research on infrasound and I'm using it today, but I didn't use it at Caltech.

ZIERLER: To bring our story closer to the present, in what ways have you remained connected to the Lab over the years, and how have you been following developments there?

RICHARDS: I stayed in close contact with Don Anderson until he died. He and his wife Nancy visited and stayed with my wife and me in New York. And I was very much a part of the small group of people that initiated the IRIS Consortium. I took a 12-month leave from academia, and I went to Washington in the Ronald Reagan Administration in the unit that analyzed claims of Soviet violation of arms control treaties. Because I was based in Washington in 1984 and 1985, the people who were about to set up the IRIS Consortium asked me to chair the effort to find the first full-time president for IRIS, an executive who would set up and run the whole consortium. I worked very closely with Don Anderson, even more than I did with Freeman Gilbert and Adam Dziewonski, to make sure that we were choosing the right president for what became a very successful operation. My committee wrote the job description for the IRIS president. We advertised, and were able to recommend very good candidates to the executive committee. They chose one of them, Stewart Smith — who, by that time, had moved on from Caltech and become a professor at the University of Washington.

He became, very successfully, for more than ten years, the IRIS president who established the overall framework in which that consortium does its good work. I stayed in touch with Caltech. There was one difficulty. A really excellent seismologist, Don Helmberger, and I unfortunately came to a disagreement over a number of years on the interpretation of seismic signals from the largest underground Soviet nuclear test explosions. The technical question was whether the yield of these largest underground Soviet explosions had exceeded a restriction on their allowed size. In 1974, the Nixon Administration had successfully, with Henry Kissinger's help, concluded a bilateral arms control treaty — just between the US and the USSR — that said yes, underground testing is allowed, but neither the Soviet Union nor the United States will carry out underground tests larger than 150 kilotons. Then, time rolled on, 1976, '77, '78, '79, and the size of the largest underground Soviet explosions appeared to some people to exceed the allowed limit, which became a celebrated cause. There were disputes, and I did not always agree with some of the things that people at Caltech and elsewhere were saying about those claims. In the end, I think it's fair to say that we concluded that the Soviets were not in violation, but at least for some period of time, there was a subset of people in the United States who were prepared to accept that there was a serious violation going on, so we disagreed with each other, and that was unpleasant.

Nuclear Testing

ZIERLER: What interface did you have with the government, with the national security authorities, based on these findings

RICHARDS: At times I was very much inside the government. I was on the team that negotiated the Comprehensive Nuclear-Test-Ban Treaty, I was a consultant with the Department of State for 30 years. I was, beginning in 1984, and still am, a member of the so-called Seismic Review Panel of a US Air Force unit and met Don Helmberger and others there. I got on pretty well with Don on a lot of things, but we disagreed on others. In the end, we came to have a rapprochement. But there were some years there where we did not get along with each other as well as we might've wanted.

ZIERLER: Without getting into details, was any of this work on what the Soviets were doing classified? Did you need special work arrangements?

RICHARDS: It's long been known that the United States Air Force has a very sophisticated unit that was given, in the 1940s, by General Dwight Eisenhower, the job of monitoring the rest of the world for signals of a nuclear test explosion. When he set that up, the United States was the only country with nuclear weapons, but the Soviet Union carried out its first successful nuclear test and became the second country in the summer of 1949. The reason the Air Force was given the lead role, was because at that time the key technology for explosion monitoring was flying planes that would pick up radioactive evidence in the atmosphere. When the atmospheric test ban treaty successfully brought an end to atmospheric nuclear test explosions by the U.S., the Soviet Union and the U. K., and eventually China and France, then these countries moved into carrying out their explosive tests underground. So the Air Force promptly developed a very sophisticated global network of seismographic stations and hired expert seismologists. The existence of that responsibility as being part of the Air Force is openly known, but the details of how they do their work is not openly known. However the seismic signals from the largest underground explosions have been well recorded at numerous openly-available stations around the world, and high-quality work is done with them that is unclassified. The Air Force arranges interaction between its own experts and outsiders to evaluate technical evidence, though there has been less of this in recent years because (as of April 2022) the last test explosion was in September 2017. We're very concerned that there might be another one in the next few weeks because, as you can read in the newspapers, we are close to the 110th anniversary of the birth of Kim Il-Sung, the first North Korean Great Leader of the modern generation, the grandfather of the present leader, Kim Jong-un. You can see in recent news reporting that the North Korean nuclear test site is undergoing construction activity.

ZIERLER: We talked earlier about the proliferation of data, even the democratization of data throughout the seismological community. What has this meant institutionally for the Seismo Lab, where so much of its history and greatness was wrapped up in the fact that it was an archive of data, that it held it almost in a possessive kind of way?

RICHARDS: It's gone through a number of changes, and I have not been up to date. I'm sure there's excellent work ongoing there. But the big change is associated with a decision by Caltech to discard its huge archive of analog recordings. The leadership in acquiring data continues today in a joint operation between a group employed by Caltech, and an outpost of the US Geological Survey across the street (Wilson Avenue). Between the USGS and Caltech, the Southern California network of modern seismographic stations does excellent work recording earthquakes in the southern part of the state, and there's a corresponding Northern California array of seismometers organized out of Berkeley. That work continues, and I have a high regard for a lot of the work that they do. But the connection to the era that I am more knowledgeable about is broken because the system operating today simply doesn't have access to the primary database needed for studies of earlier earthquakes and nuclear test explosions documented only in the analog archives that were discarded.

ZIERLER: To bring the conversation right up to the present, in the way that when you were a graduate student at Caltech, and seismology seemed wide-open, there was so much low-hanging fruit, for today's young scholars, what is their low-hanging fruit in the field?

RICHARDS: There are a lot of separate studies of particular source regions, where the need is to understand how long a particular fault system has been active. Has it had earthquakes for the past one million or ten million or 50 million years; and has the pattern of seismicity changed with time? The answer is different for different regions. A large-scale project from which the whole community would benefit would be to update the methods of analysis applied to modern data coming from the type of Southern California, Northern California networks I just briefly described, in which we face a strange situation today. Earthquakes are still being located, for the most part, one at a time by the traditional process of using the arrival time of signals at a set of standard stations, interpreted by some model of those travel times. I think a better way to do it would be to use the whole wiggly waveform and make precise measurements of the signals from all pairs of earthquakes that are close to each other, and in this way, achieve a precision of how each earthquake is related with reference to its neighbors.

This isn't a small project, you understand. This is a project of doing something on a large scale that would be a community resource, so that we would see a radical improvement in the characterization of the many earthquakes that happen on a daily basis. That is something perhaps harder for an individual graduate student to make an impression on. He or she can perhaps study an area of interest. But to apply modern methods of analysis on a large scale would take a team of people, and I think it would be wonderful if some government agency or academic institution would have an Ernest Lawrence or Adam Dziewonski kind of figure who would crack the whip and build a whole team to do a level of analysis that, instead of having a cottage industry of umpteen different campuses all doing a half-baked kind of effort, would bring together a team and provide a product that would elevate the quality of everybody's work. That's a large-scale thing. That's not low-hanging fruit, it would take quite a team to do that.

ZIERLER: For the last part of our talk, I'd like to ask a broadly retrospective question about your career, then we'll end looking to the future. In all of the things that you've done, what do you consider settled science, and what remains up for debate? What is not yet settled?

RICHARDS: The framework of plate tectonics became settled in the late 1960s, and we continue to work out more and more of the details. But the overall framework is well-established. Some of the details of the way subduction zones work are still subject to the possibility of future improved understanding. At some level, I'm tempted to waffle in answer to your question, but at some level, I'm reluctant to do it. An old man pontificating about things that really are just speculation. I gave you an answer just now that was much more detailed because I know something about the level of improvement that could be achieved if people took locating earthquakes more seriously than they currently do. But I'm reluctant to accept your invitation, David. [Laugh]

ZIERLER: [Laugh] Fair enough. Finally, looking to the future, what else do you want to accomplish, for as long as you want to remain active in the field?

RICHARDS: I don't know how it's going to happen because this is not science. The big picture: is it climate change, nuclear weapons, too many people in the world? When I was born, there were 1.5 billion people in the world. Now, it's approaching eight billion. I know people are concerned about economics. Every economist I know seems to take it as written that we need to grow at least 5% a year. I just think that's ridiculous (it would lead to doubling the economy every 14 years, and that can't be sustained). I don't quibble with the people who say that climate change is really important, but I think the problem with nuclear weapons is so serious. It's a technology that, if it's used, addresses the population problem and brings nuclear winter. That's terrifying. The top three issues, to me, are nuclear weapons, how many people are appropriate for our very special planet, and climate change. To me, they're all related. When I was a student (we didn't talk about this yet in this interview, but) California politics and Vietnam laid its hand as a political background to almost everything that was going on. The faculty parking lot at Caltech had Reagan stickers all over the cars (when he was running for Governor). At the time, the kind of activity that we see today in Ukraine, the United States was doing to Vietnam.

We haven't talked about that. It's not a practice at Caltech to talk about things like that. It's very confrontational to talk about things like that. But at some point, we won't have any choice to talk about it. It's not a comfortable thing, especially for somebody who's got the job that you currently have, to go in that direction. But those are the things that really matter. I don't know, at Caltech, what the current generation of graduate and undergraduate students puts its effort into. I wandered around the campus a couple of years ago, Dabney House, where I spent two years, and it's so different today with all the signs about exploration of the personal lives of students, making sure that they had permission from each other to do what they might be inclined to do. It's fine, but the things that mattered so much when I was a student, I was there in the era where every American in the graduate school was there largely because they had some type of deferment; and once they graduated, what would be their draft number, and what level of problems would they face with their local Selective Service Board?

At Caltech in the 1960s, my wife was a draft counsellor with the American Friends Service Committee, and I joined various protests in California when I was a grad student. As I've mentioned, I was married in a Quaker meeting. They have a very distinct approach to weapons. [Laugh] They don't want them.  (I'm an Episcopalian  myself — in Pasadena in the 1960s I sang in the choir of their huge church on Euclid Avenue.) There were issues later on campuses across the country, expressing concern with nuclear weapons development, and promoting the nuclear freeze movement, which I worked on in the early 1980s at Columbia with I.I. Rabi (another Nobel laureate in physics, who had participated in the Manhattan Project).  In the 1990s I found my way into heavy political scenes in the State Department and international test ban negotiations in Geneva.  In about 2003 I initiated (and taught for ten years at Columbia) a new course for undergraduates, on how weapons of mass destruction work, what effects they have when they're used, and what technical work is needed to attempt to control them. And it bothers me now that young people, of course, are appropriately concerned about climate change — but let's not forget that nuclear weapons can really spoil your whole day.  I grumbled earlier about the short-term focus of economists. I'm too old to get deeply into what the right answer is, with these big questions, but it's not just about climate change.

ZIERLER: And unfortunately, the problem of nuclear weapons has gotten a lot more real in the past few months.

RICHARDS: Yes, indeed. This is one hell of a way to solve the population problem, but it could be that.

ZIERLER: Oh my goodness. I hope you're wrong. [Laugh] Paul, it's been a great pleasure spending this time with you. I'm so glad we were able to do this. I'd like to thank you so much.

[END]