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Charles Langston

Director and Professor, Center for Earthquake Research and Information, University of Memphis

By David Zierler, Director of the Caltech Heritage Project

April 6, 2022

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Wednesday, April 6, 2022. I am delighted to be here with Professor Charles Langston. Chuck, great to see you. Thank you so much for joining me today.

CHARLES LANGSTON: It's my pleasure.

ZIERLER: To start, would you tell me your title and affiliations here at Caltech?

LANGSTON: Currently, I'm director of the Center for Earthquake Research and Information at the University of Memphis. And Professor.

ZIERLER: How far back does the Center go at Memphis?

LANGSTON: It goes back to 1977, but it officially became a Tennessee Center of Excellence in 1984.

ZIERLER: Are you familiar with the origin story of the Center, why it came to Memphis?

LANGSTON: Roughly, yes. There was an earthquake. I believe it was in 1976 or 1977 about 40 miles from Memphis. It was only a magnitude 4 earthquake, but it caused damage in the city of Memphis. The state of Tennessee thought this was important. The University of Memphis was called Memphis State University back then, and they basically started the first research project at the University, in my understanding, funding a couple people to set out a seismic network in the region. That grew as it became more recognized that there were more earthquakes in the New Madrid Seismic Zone. Just before 1984, Governor Lamar Alexander at the time, who later became a Senator, started an Academic Center of Excellence program for all sorts of different centers around the state. The University of Memphis has five of these centers. The Earthquake Center here was one of those centers that started up.

ZIERLER: How long have you been at Memphis?

LANGSTON: Since 2000.

ZIERLER: Did you come in to be the director?

LANGSTON: No, I came in as a visitor, and I stayed.

ZIERLER: Some overall questions about your research. What are the main areas in seismology and geophysics that you focus on?

LANGSTON: I'm basically a seismologist, coming out of the Seismo Lab. I've worked on a lot of different problems, including wave-form modeling for source parameters, earth structure. I've concentrated more on crustal structure, I think, over my history of work, more of the shallower earth than the lower mantle and core. Lately, I've been working on different kinds of array processing techniques, getting into wavelet transforms, noise reduction for seismograms, and doing field experiments as well.

ZIERLER: A nomenclature question, what are seismic waveforms?

LANGSTON: When an earthquake happens or something disturbs the earth, seismic waves go out from the hypocenter of the event, like P-waves, S-waves, and Rayleigh waves are set up near the surface of the earth. That ground motion propagates out to a seismic station someplace. The seismic station consists of a seismometer, which in its simpler form, is a mass on a spring, and it vibrates, and that vibration is measured. We basically measure the vector motion at the surface of the earth, usually. There are other ways of measuring seismic waves, but that's generally the common one.

ZIERLER: As a layman, I might take an educated guess as to what earth structure means. As a seismologist, what does that term mean in your field?

LANGSTON: Generally, that means how seismic wave velocity varies within the volume of the earth. For example, the crust is about 40 kilometers thick under continents. It has a slower compressional wave velocity than the mantle, which is deeper. In the order of magnitude of numbers, P-waves travel at six kilometers per second in the crust and eight kilometers per second in the mantle. And that velocity varies because the history of the earth has complex geology, plates have collided, mountains have been built, oceans produced. The velocity of seismic waves changes from place to place, and that just means that the material properties are changing from place to place.

ZIERLER: At a general level, what role does theory play in your research, and what specific theories are most relevant for the kind of work that you do?

LANGSTON: I've always had a very theoretical streak. Data is always very important, but you need some very rigorous theory to back up what you say about the data. One of the things I got out of the Seismo Lab when I was a student was rigorously solving the wave equation to determine how the waves actually propagate in different kinds of seismic structures so that you could generate much more realistic seismograms, theoretically, to try to match to the observed data. Theory goes into making what you think happens in the earth, then you compare that to the data in order to make a better model of the earth and maybe model the source of the seismic waves.

ZIERLER: Over the course of your career, what have been some of the most important instruments, and what have been some technological advances that have allowed you to pursue new research questions?

LANGSTON: I've been doing Seismology professionally for 45 years, not counting the time I was a student, and that's a heck of a long time. It's almost like being born before the Wright brothers and flying, I think. When I was a student, one of the drawbacks or sources of problems was that you could not get data very quickly. Data was not digital, so a seismogram was actually a piece of paper, and it would have to be photographed by somebody, then that film chip of the photograph would be sent to you, and you would have to digitize it and do stuff with it. Seismic data has changed considerably. From paper records, it's gone digital, and the type of instrument has improved immensely. Original instruments were very narrow band, they only recorded certain frequency bands. Today's instruments record a very broad frequency band so that we can see seismic waves at almost any wavelength or frequency. That's been one really major development that's improved the whole field. There have been other kinds of instruments that have been invented as well, strain instruments, which are still undergoing research, rotation instruments, where you measure the twist of the ground, as well as making instruments smaller, much more portable, and cheaper, so you can put many more out to do particular seismic experiments. All those things have been extremely important in my research and also in the field in general.

ZIERLER: What have been some of the key institutional partners and funding sources who have supported your work over the years?

LANGSTON: I was at Penn State University for 23 years before I came to the University of Memphis. They were quite helpful, as well, in my career. I've had grants from the National Science Foundation, the Department of Defense through Air Force Research Lab out in Albuquerque, AFOSR, DOE. DOE and DOD have extensive programs in nuclear verification research, basically quantifying and detecting underground nuclear explosions, which has been kind of a theme throughout my career as well. The US Geological Survey has been very important as well. Since I came to the University of Memphis, I've had a number of USGS grants to do earthquake hazards-related problems in the Central United States and elsewhere.

ZIERLER: You mentioned 45 years. I'm curious, generationally and intellectually, where do you situate yourself regarding plate tectonics?

LANGSTON: That's an odd question. [Laugh]

ZIERLER: Meaning when plate tectonics became to be recognized as accepted science.

LANGSTON: When I was an undergraduate at Case Western Reserve University, I went to a meeting that was at Oberlin College, not too far from Cleveland, and there were arguments about plate tectonics. The paleontologists said, "No, plate tectonics is garbage." Geophysicists started saying things about earthquakes and other things, and that's when I became interested in geology and geophysics. Then, it quickly solidified and became an operational paradigm, certainly when I went to grad school, which started in 1972. It was a big change over those few years, and I guess I knew of and certainly met not too much later some of the original seismologists and geophysicists who worked on plate tectonics as a comprehensive theory.

ZIERLER: But prior to that, by the time you got involved in this research, continental drift was accepted, that was mainstream at that point.

LANGSTON: I think so, yes, it was mainstream.

ZIERLER: How do you understand the sequencing? Why would continental drift become mainstream before plate tectonics?

LANGSTON: Wegener said that continental drift could happen. There was a lot of opposition to that, so it wasn't accepted.

ZIERLER: Meaning that before Wegener, there was no notion of a Pangaea, no concept that the world we see today somehow looks different than it would have hundreds of millions of years ago.

LANGSTON: I don't think so. I don't think that concept was like that. I think geologists would think, because of the rocks found on continents, that certainly continents were submerged at one time. They go up and down. But they haven't really moved substantially from one spot. I guess the earth could look differently, but fundamentally, if you took the water away, you'd still see the same continents.

ZIERLER: Let's go back and develop the historical narrative. When you were at Case Western, did you want to study geology as an entree to geophysics? Or was the plan that you would pursue a career in geology itself initially?

LANGSTON: At Case Western, I originally went to Case Institute of Technology, then they merged with Western Reserve University while I was there. I was in an engineering school for the first two and a half years. I liked some of the engineering, particularly the fundamental math and physics courses. But I went into a course on material properties on the stress and strain of materials, basically, and the engineering instructor looked at us and said, "This class is way too big. I'm going to have to get rid of half of you," or something like that. That just turned me off completely. I was getting kind of discouraged because it just wasn't interesting enough. At Case, there was an intercession of one month between semesters. I looked at the catalogue and saw a geological field trip to California in the month of January, and I thought, "Yes, I am getting out of town. That's exactly what I want to do." But the prerequisite was, you had to be a geology major, so I switched my major from engineering to geology, went on the trip, and never looked back. I loved geology, I loved technical stuff, the math and physics that went along with engineering, but the other thing at Case was that we took basic programming. At the time, you dealt with computer cards and I just hated programming and computers. I disliked the idea of seismology because it just sounded too dry. I vowed while I was at Case I would never work on a computer or become a seismologist. I've learned since then never to say stuff like that because that's exactly what I did when I went to Caltech.

ZIERLER: How did it turn around where you ended up going to a seismology program?

LANGSTON: It was just exciting being at Caltech and doing something real, what I thought was real science in some way. When I started taking the courses, it was the math and physics, which really surprised me because I never thought I was particularly strong in math or physics, but I loved it. The more intricate it was, the better I liked it. I was actually doing research for homework, and that turned into papers with Don Helmberger. I enjoyed it and really got into it, so it became my own. It's been like that ever since.

ZIERLER: When you were thinking about graduate school, did you have professors who suggested looking at Caltech? Or did you find it on your own?

LANGSTON: I'd always been interested in Caltech, but the professor who took us out to California was a graduate of Caltech in geology. I think he might've been a Lee Silver student, and he eventually moved from Case and went to Michigan Tech on the Upper Peninsula. Doug McDowell. There was another geochemist at Case as well. There was kind of a Caltech connection.

ZIERLER: What were your initial impressions when you arrived at Caltech?

LANGSTON: I'm not sure I can remember that far. [Laugh]

ZIERLER: Was the Seismo Lab an exciting place? Did you get that sense immediately?

LANGSTON: Oh, yeah. Definitely. I came in the summer before the semester started. I got there early, and they allowed me to start up. I worked with Don Helmberger over the summer, looking at some data, reading seismograms, starting a couple of projects. I was just trying to figure out things. But there were a number of people who came through the lab who were quite interesting, so I knew it was kind of a junction place where people would visit, do a little bit of research, then go someplace else. We had the run of Donnelly Lab in the San Rafael Hills. That was a wonderful place because all the students were kind of in a bullpen in the big dining room that overlooked Pasadena. We just had a ball. It was really nice to work there.

ZIERLER: What were the big debates happening at the Seismo Lab when you arrived?

LANGSTON: When I became aware of more of the science, after taking a couple of courses the first two semesters or so, then seeing what people were doing for their science, whole earth models were on the uptick. That means pulling together big datasets of travel times from body waves and surface-wave dispersion to make a more detailed model of the entire earth. Don Anderson started to get involved with that. The problems I was associated with were computing synthetic seismograms with Don Helmberger and David Harkrider. I got in on problems of wave propagation in the earth related to verification research and nuclear tests. My first project, in fact, was a recording of a nuclear test at the Nevada test site at the time. There was an array of seismometers put out by the technicians at Caltech of only eight or nine stations. But I took that data, I modeled it a couple different ways, and my first paper was on that research. That was kind of a beginning. Parameterization of earthquake sources was just starting then in a more rigorous way. That's where I did my thesis research. That was my general field there. It was wave propagation and sources that I was most directly influenced by.

ZIERLER: Coming in with a geology background, how much catchup might you have had to play relative to other grad students who might've had more geophysics and seismology as undergraduates?

LANGSTON: Actually, the problem was just the opposite. The people who had only a math and physics background, or maybe even geophysics, had to go do field mapping. [Laugh] I'd already done it. I went to field camp, and I loved it. I think I was a real anomaly because I was a geologist by training, but as I look back, I had an excellent technical background through Case. When I was at Penn State University, we would get applications for students who wanted to go to grad school. Every time we got one from Case, I was amazed how well they were prepped. Even the paleontologists were taking differential equations, thermodynamics, and everything. It was incredible. Every other big school paled in comparison to it. I just went to the right place, I think, to get that background.

ZIERLER: Between the instrumentation, the data that was available at Caltech, and just the overall intellectual environment, in what ways was the Seismo Lab a magnet for people beyond Pasadena in the field?

LANGSTON: Well, there was Don Anderson, who was very famous for what he was doing. There weren't that many schools in geophysics at that time. Since then, there have been many more as all the students have gone out and gotten jobs. But there was basically Caltech, Columbia, Berkeley, MIT, to some extent, a couple other places. I guess UCSD also, a very strong place. It was a center, and visitors would come. I saw several post-docs and scientific visitors while I was there. They would come and look at the data. We had archives of data. There were paper records, but we had a great archive of microfilm film chips that you could sift through, look at lots of different earthquakes and other events, then do things with the data. It was kind of a data center that was tailored to actually do seismic research. It was a good place just to come and visit for that reason.

ZIERLER: As you said, despite your best-laid plans, you did end up working with computers in seismology. What did computers look like, and how did you use them as a graduate student at the Seismo Lab?

ZIERLER: What was the sequencing for you? Did you choose a thesis advisor first, then focus on a topic? Or did you work on topics, and that led you to a thesis advisor?

LANGSTON: The ambiance of the lab created the topics. The grad students were accepted and they were given advisors. I never thought that was a serious thing, like you were beholden to your advisor in any way. They were there to advise. I worked with Don Helmberger for a while. But you were treated as an equal and working on things you were interested in doing, and it sort of naturally turned into something where you were working on a synthetic seismogram, you were going to be either working with Don Helmberger or Dave Harkrider. I worked with both of those guys, and there was never any kind of territorial advisor-student thing going on. I never felt that. Anybody could work with whoever they wanted to depending on the project.

ZIERLER: Where was there overlap in your advisors' research, and where did they have separate interests?

LANGSTON: Dave Harkrider specialized in surface waves, and Don Helmberger specialized in mostly body-wave propagation. Of course, the seismogram has both of those things in it, so I dealt with both advisors. They were theoretically distinct a bit as well. They had their own niches in the theories they were using, and programming, and creating their synthetic seismograms. At the time, you had to be fairly specialized like that because it was so difficult to do any of these computations. It was a very natural split.

ZIERLER: What were the topics that ultimately formed your thesis?

LANGSTON: The thesis itself, there was a theoretical aspect, then the data aspect. The theory came out of courses I took in theoretical seismology, but I did not have a clue at first on how I would actually use that to make a thesis. I had to do a lot of my own research on the side, perusing journals in the library. I came upon a couple of really interesting papers because I was going through Journal of Geophysical Research and saw that there was this particular earthquake in India in 1965, I think. It was a magnitude 6.5, and it killed 200 people. I thought, "Wow, that's interesting. Sounds like a terrible disaster." The interesting thing was, it seemed to be associated with the impoundment of a reservoir. They built a dam, filled up a reservoir, and earthquakes started. That was the first indication of induced seismicity I had come across. That became interesting. Then, I saw where the Indian government had claimed, "This earthquake had nothing to do with the reservoir, and it was very deep." I thought, "What?" It didn't make sense, so that really got my interest. I had to study that earthquake. We had the data in our film chip library, so I went and got it, I looked at it, I looked at the body waves, which I had started to make models of in general from my theoretical seismology work, and I said, "No, that earthquake is really, really shallow," just by looking at it. That got me more interested. And that drove the scientific direction of the thesis. Modeling earthquakes, their body waves, to figure out the source orientation of the faults, how deep they are, and how long they move, that sort of thing, really became a focus. Other topics grew from that in terms of the wave propagation. How do you explain the waves that you see and some of the anomalies in the data? It was a combination of a couple things.

ZIERLER: Were there aspects of your thesis research that were oriented toward ultimately earthquake detection?

LANGSTON: Not detection per se, it was more quantifying earthquakes. Towards the end of my stay at Caltech–when did Star Wars come out?

ZIERLER: Late 70s?

LANGSTON: Yeah, like, '77 or something. Anyway, the USGS started to get interested in using these modeling techniques to actually put them online, which they've done since. Nobody does this stuff usually anymore. It's routine. There are automatic algorithms that take the data. When an earthquake occurs, the data are collected digitally, thrown into the pot, and you get a waveform model basically using the kinds of things I was working on back then.

ZIERLER: What were some of the big debates, and how do you see your thesis research as contributing to them at that time?

LANGSTON: The big debates I recall occurring at the lab having to do with seismic sources were centered around how a nuclear explosion can excite certain kinds of waves that only earthquakes excite. Some large underground explosions look like earthquakes sometimes. There was one professor there, Charles Archambeau, who came up with a source model. The debate was around his source model that had a pressurized cavity at the explosion point, then there was another boundary outside of the cavity where stress would change. He came up with a model in which he could explain some of this tectonic effect, essentially. Turned out his student, Bernard Minster, showed that the model was not exactly wrong, but inappropriate because his model included the explosion part, but the extra boundary also made another source that was artificial.

There was debate on what was wrong with that model, what was going on, all related to the tectonic release problem in underground nuclear explosions. Where do these waves come from that make it look like an earthquake rather than a pure explosion? That was one debate that was related to what I was doing. If you could model a source better with synthetic seismograms and realistic models of the earth, maybe you could come up with an answer for some of these things. Another debate that occurred towards the end of my stay there. Bernard Minster became a professor at the Lab, and he worked on two things I thought were really quite good. One was the effect of attenuation on biases you see between earth models created with body wave data compared to surface wave data. His attenuation model showed that there was a phase shift that could adjust for those biases, which was really kind of neat. The other thing he worked on was the source problem as well.

Tom Jordan and Bernard came up with a way to model plates' motions simultaneously with all sorts of different kinds of geophysical data, spreading rates at mid-ocean ridges, the trend of oceanic fracture zones, seismicity rates, I think. They came up with a nice inverse formulation to do that, which many people have basically taken and used over the years. That was very nice. When Tom Jordan was a student and towards the end of his tenure, he got involved with the stochastic inverse. Inversion theory started to become a thing in geophysics, and I think seismologists pushed that with modeling big and strange datasets. Part of my thesis was applying inversion theory to model earthquakes.

ZIERLER: Looking back, either by the kinds of research questions you were asking or the way you were going about analyzing the data, do you see that you were representative of a unique school of thought that was unique to the Seismo Lab?

LANGSTON: Yeah, I do. I think the idea of making synthetic seismograms really took hold at the Seismo Lab with Don Helmberger in particular. I was just the first student to jump onto his wagon, but there were many who came afterwards who continually used the idea of rigorously having a theoretical framework to make a realistic seismogram to compare to your data. That was a new thing because you needed digital data, which was hard to come by. We had to create our own digital data by hand. We would digitize point by point seismograms. You'd be hunched over a digitizing table for hours to digitize up a number of seismograms that you could then take to the computer and model. Because of that, that was really a new thing. I think that was certainly one of the contributions of the Lab at that time.

ZIERLER: What opportunities were available to you after you defended?

LANGSTON: I looked at a number of jobs. I could've gone to Lawrence Livermore National Lab. They gave me a job offer. I could've become a post-doc at Lamont-Doherty. I looked at that and wasn't happy with the small pay, I guess. Lawrence Livermore looked pretty good. But I really wanted to go into academics more than anything just because of the freedom of pursuing research that I wanted to do. That's when that Penn State job opened up. I also interviewed at University of Arizona for a faculty job. I didn't get that one. But I did go to Penn State.

ZIERLER: Did Penn State have a big program in seismology and geophysics?

LANGSTON: It wasn't particularly big, but there were about five, six people there. It was a smallish program, but it was nice.

ZIERLER: When you joined the faculty, did you take an opportunity to pursue new fields of research, or did you continue on the path from Caltech?

LANGSTON: Initially, I continued on that path from Caltech. One of the things I did at Caltech was model the effect–this was with Larry Burdick, who was another grad student there at the time–of the crust on incident waves that come up from underneath. While I was at Penn State, I came up with a method to remove the unknown effect of the seismic source so that you could see the response of the crust more clearly. I think everybody in the world now uses that. [Laugh] There are just hundreds of papers on what's called the receiver function technique. That was a new thing, but that grew out of what I was doing at Caltech. I did more of the same for a while, but then gradually, at Penn State, I was interested in wave propagation, so I was becoming better, and branching out, and looking at different parts of the earth, different kinds of wave propagation, more details, computational methods, to model more complex structures. But I didn't get into actually collecting data very much until I came to the University of Memphis, and that's where I think going out into the field, designing seismic experiments, collecting data for particular reasons, other kinds of scientific reasons than just doing better theory and more accurate seismograms.

ZIERLER: Why, at that stage in your career, did you start collecting more data? What was going on at that point?

LANGSTON: Penn State is a nice place. I don't know if you've been to Happy Valley or not, but it's very happy there. [Laugh] You can sit around being happy. Maybe it was just my situation. I take it back, let me take a little bit of that back because I got a post-doc who was interested in working with me at Penn State, Andy Nyblade, now the department chair there. He was interested in working with me because he wanted to do an experiment in Tanzania. That's when I really had my first experience with putting out instruments and collecting my own data, and that was a blast. That was really, really fun. We went to Tanzania, I was there for a month for one of the service runs, running all over the country in an off-road vehicle, seeing animals, getting data. We went back to geology, in a sense, getting out into the field.

ZIERLER: How long did the initial visiting appointment at Memphis last?

LANGSTON: One year.

ZIERLER: What were the circumstances of staying on?

LANGSTON: They seemed to like me. I had started to become a bit tired of being in Happy Valley for all that time. When I was at Memphis, it was a completely different dynamic. The program was larger. There was a seismic network here, so people were collecting data. We went out and collected data while I was here as a visitor, and I really got interested in some of the scientific problems. It seemed like finding a new sandbox to play in in a very literal sense because we sit on a kilometer of sand here pretty much. We have big earthquakes occasionally. The last were in 1811, 1812. There are some fairly significant scientific problems that haven't been solved yet.

ZIERLER: Such as what? What stands out in your memory that had not yet been solved?

LANGSTON: The thing I started working on was, when an earthquake occurs, theory says that the seismic waves that come up from the earthquake to the station get amplified if you have lots of thick sediments that have low seismic velocities, yet they won't be amplified if those sediments attenuate and absorb the energy. There's still an issue of whether these sediments will amplify or attenuate strong ground motions. The engineers think they'll mostly attenuate. As a seismologist, I'm not so sure. [Laugh] That's one of the problems. I've heard some positive news that I'll be funded to do an experiment this year, which will address that exactly, where we're going to set out 60 seismic instruments not far from Memphis, over in Arkansas, and have two explosions on either end of this array of instruments, and measure and model the seismic waves to look at this exact problem of attenuation.

ZIERLER: Beyond moving institutionally, in terms of a greater understanding of your entree into more observational work, collecting data, what were some of the technological advances in instruments that might've been relevant for this switch for you?

LANGSTON: Broadband instruments were certainly relevant, and they were getting more portable.

ZIERLER: What does broadband mean seismologically?

LANGSTON: A broadband instrument is an instrument that measures the frequency of seismic waves' ground velocity from a period of 100 seconds all the way up to a frequency of 100 Hertz, which is 1/100 seconds period. That's quite broadband. And they're also small. The instruments used to be monsters, you couldn't lift them up. Now, they're little cans like this, and you can go put them wherever you want. They're much more portable.

ZIERLER: Did you take graduate students with you when you got to Memphis?

LANGSTON: I did. I took one, a Korean student.

ZIERLER: Administratively, how is the Center at Memphis set up? Are there professors who have home departments? Is the Center their own home department?

LANGSTON: Right now, the Center for Earthquake Research and Information is essentially its own department and an earthquake research center at the same time. We have our own portion of the earth sciences graduate program, which is in geophysics. We have our own promotion and tenure committee, so people are promoted or tenured first through the Center. The path is the Center, the college, the provost for the administration. We're related to the Department of Earth Sciences at the University. I think we all have nominal titles of Professor of Earth Science at the Center. But administratively, and this grew out of money problems, as you might expect from any academic arrangement, there was confusion on how resources should be allocated. The Earthquake Center gets money directly from the state for particular reasons. Approximately about a million dollars per year, it hasn't changed too much. The University contributes roughly another $500,000 to$750,000k per year. Our primarily responsible is doing research, and we're actually written into state law. One of the things that's written into state law is that we should be predicting earthquakes. That's always an interesting thing to try to sidestep when the legislators are asking us, "Have you predicted earthquakes yet?"

ZIERLER: I can't help but ask, given your proximity, was the Center at Memphis particularly well-positioned to understand the 2011 Virginia earthquake?

LANGSTON: We initiated a field program that started here, then the USGS came in on it and some other people around Virginia, so yeah. We do that. If a fairly significant earthquake, magnitude 5 and above, happens anywhere in the Central or Eastern US, we'll go see it and do something with it.

ZIERLER: I'm originally from the East Coast. I remember feeling that earthquake and immediately thinking to myself, "I didn't understand that earthquakes can even happen on the East Coast of the United States." What were some of the big misconceptions about earthquakes that you might've been well-positioned to discuss at that time?

LANGSTON: We're always trying to educate the public, that's one of our goals at the Center. I guess it's not a misconception, but the earthquake was kind of a wakeup call for people in Washington DC. There was damage there, the Washington Monument and Cathedral in spots, which was unexpected. The fact that a fairly moderate earthquake, it wasn't that large, could be felt and cause damage over such a large area was a demonstration of the power of earthquakes in the Eastern US. One of the reasons the Center is here is because of 1811, 1812. They were probably magnitude 7.5 earthquakes, at least three, probably more, that were felt to the East Coast. We're always trying to say what the difference is between earthquakes in the West compared to the East. I think people appreciate that. Earthquakes can happen anywhere. That was another thing, this was kind of an unexpected spot for this to occur.

ZIERLER: Now living in California, I can appreciate people here always talking about waiting for the big one. Is that also true on the East Coast, and it's just not as well understood or appreciated?

LANGSTON: I don't think people are waiting for it. [Laugh] People don't feel earthquakes as much. Unless you live right in the seismic zone up in New Madrid or someplace, you will feel earthquakes a few times a year, small ones. But generally, people don't feel them. If they don't feel them, they're not going to be thinking about them. I don't think people are waiting for it per se like the West Coast. But even the West Coast waiting for the big one–Tom Heaton has a saying he always says when he hears someone's waiting for the big one. "Well, at least three generations of seismologists have gone to their graves waiting for the big one." [Laugh]

ZIERLER: What's the bigger story there in the broader debate about whether earthquakes are even cyclical, whether there's a pattern that we can look for?

LANGSTON: That is the problem. We don't know enough about the details of how rupture occurs, the physics of earthquake rupture, to know what conditions will lead to the earthquake. We have all sorts of theories, ideas, gut instincts, and so on. But earthquakes still look to be random. Almost all of the ones in California have occurred in places people didn't expect. They always say, "Ah, we should've known this." Like Ridgecrest. It didn't look like a normal earthquake, and there it was, rupturing two different fault segments, both right angles to each other. It's just crazy-looking.

ZIERLER: How far back can we go in history before human artifacts, writings, architecture, to give a sense of how often earthquakes occur?

LANGSTON: Paleoseismology does a fairly good job of that. Around here, when a big earthquake occurs, it occurs underneath the river floodplain, and it creates liquefaction, so you get basically sand volcanoes. The ground shakes, the water pressure in the water table increases, it breaks out of the ground, and you get these spews of sand all over the place. Those can be dated with radiometric age dating methods. Around here, there have been earthquakes back to 2,000 BC or so just based on geological evidence. Where you get the correct geology, you can do some of that kind of dating. You don't always need artifacts.

ZIERLER: To bring the conversation up to the present, what are some of the big research projects you've been focusing on in the past few years?

LANGSTON: I got interested in strainmeters and applying the concepts of strain and rotation to study seismic waves. I've been interested in that, I've had a couple of grants looking at plate boundary observatory strainmeters, trying to calibrate them and using them. Basically, a single instrument can be used as an array to figure out how a wave can propagate across it. The instrument can be a strainmeter or rotation meter.

I had an excellent student, Mostafa Mousavi, who's getting the Charles F. Richter Young Investigator Award with the SSA this year. He was an interesting guy. He came in, he started trying to detect micro earthquakes, and he got interested in wavelet transform theory. I thought he was crazy. "What are you doing?" [Laugh] Because I didn't understand it. He'd write up something, and I'd have to dig through his paper and understand what he was doing. This is a case where the student was teaching the teacher. I got really involved. It became very exciting. I was doing wavelet transforms, noise reduction, and array processing. I just had a paper come out last year using continuous wavelet transforms to do seismic array processing and noise reduction, and decomposition of seismograms. This all goes back to Caltech. In fact, the very first day I walked into Don Helmberger's office, he slapped some seismograms down and said, "We want to study this." I said, "OK, what is it?" I've been asking that question ever since. "What is that wave? Where did it come from, and how fast is it going?" I've been working on that problem ever since. All of the theory of wave propagation, strain, rotation, and array processing has been to answer that question for myself.

ZIERLER: What is it about the question that has captured your attention all these years?

LANGSTON: I have no idea. I must be crazy.

ZIERLER: Obviously, it's a very difficult problem.

LANGSTON: It's very difficult. I've always wondered if there are better ways to actually observe seismic waves. After all, we can use our eyes to look at our computer screens, recognize spaces, and stuff like that. Why can't we do that with seismic waves? That's really where a lot of the research today is, trying to make images of earthquake sources using seismic waves. We're not even up to the level of simple images like we can do with our own eye, so there's still a lot of progress to be made.

ZIERLER: Do you think quantum science, and specifically quantum sensors, might be a game-changer for this?

LANGSTON: I don't understand enough about it. [Laugh] I read a little bit about quantum computers, which may speed up computations quite a bit. I'm not sure what a quantum sensor is, though, so I can't answer that question.

ZIERLER: For the last part of our talk, a few questions about the Seismo Lab in a retrospective sense. First of all, have you kept up with the Seismo Lab over the years? Are you aware of what's been going on?

LANGSTON: There'd be some years when I wouldn't pay too much attention. I usually look at the website, see who's there, what's going on. But not in great detail. Not until Don passed away and I was wondering what was going on with people there.

ZIERLER: I've heard one of the things that the Seismo Lab was, which isn't true today, is the fact that seismological information is available to everybody because of the internet and computers, so it has sort of decentralized the field such that places like the Seismo Lab, by definition, don't need to be as prominent as they once were. I wonder what your sense is about that.

LANGSTON: I think that's completely true. The Institution of IRIS, for example, and their data practices, it's fantastic. You can be anywhere and do great science. That's why there are so many programs around the country with good people in them. The science is much more egalitarian, I would say. Back when I was a student, if you collected data, that's what you did, and you hoarded that data because it was valuable. You didn't give it to people. Science didn't really advance that quickly because of that. But because we have places like IRIS and this open-data policy, it's astounding what you can do. I think you have to be really, really smart and have something that's really, really different to have anybody notice you these days as a center that does a certain thing.

ZIERLER: This is well after your time, but when you were at the Seismo Lab, did you feel the legacy of people like Richter and Gutenberg? Was that sort of felt in terms of what they had created generations earlier?

LANGSTON: While I was at the lab, I saw Charlie Richter a number of times. I didn't see Gutenberg or Benioff, they had died of course. But I got the idea, yeah, there was a continuity there of things that went on. But it's only been recently, in the past five, ten years, that I've gotten an appreciation for how Don Anderson, for example, was really a definite product of that original era, and he carried on that kind of scientific program that they had started. When I finally looked back more broadly at who was there and what they did, where Don Anderson actually came from (because he was the director of the Lab at the time) did I really get an appreciation that that legacy was very, very strong. All the time, it was there. But I didn't recognize it. I have to admit it, I didn't recognize that. Although, we did play "Benioff ball" in the library, which was basically throwing a tennis ball into a wastebasket across the room when we were tired of working on our programs or whatever. We knew who was there and what they did. [Laugh] Certainly, Richter was always on our minds.

ZIERLER: Thinking about your time at the Seismo Lab and some of the orthodoxies or accepted science during that time in seismology, what the Seismo Lab represented, in the subsequent years, what has held up the strongest, and what have been some real changes in the field?

LANGSTON: For the things I was working on back then, I think they've become commonplace now. You do something, and you become part of the scientific woodwork. People just use the stuff. And sometimes you don't even get referenced. That's OK. People just do it, and you know where it came from. I think that's certainly carried on to the present day. One thing - towards the end of my time at the Lab, we all thought earthquake prediction was going to be solved in ten years or something like that, and that certainly didn't come about. [Laugh] Some of the earlier earthquake prediction efforts, like Jim Whitcomb's Vp-Vs anomalies and the Palmdale Bulge - those kind of evaporated. And we're still in the same boat. We can't predict an earthquake. That's still an outstanding problem that hasn't been solved.

ZIERLER: What do you think it's going to take? What are the advances in theory and instrumentation that will make earthquake prediction feasible?

LANGSTON: I've always thought that seismic instruments won't do it because that's (the data) after the earthquake. There has to be something where you get an identified precursor to it, and it could be we don't have such an instrument yet. A really cutting-edge project would be to set out all sorts of harebrained instruments where you just can't imagine how you could measure a signal, but put them out and empirically see what clicks before the earthquake. People don't want to do that. It costs money, you don't know how long it's going to take, you don't know what the signal's going to be. I think whatever it is, I don't think we have the instrument yet that will allow us to predict an earthquake.

ZIERLER: Would you say that's the holy grail in seismology, where the field is right now?

LANGSTON: That's one of them, sure. That's the easy one. That's what normal people want, and it's a really good thing to do. It is sort of a holy grail. How do you get to that holy grail? What kind of penance will you have to do? [Laugh] What monster do you have to slay?

ZIERLER: Last question, looking to the future. As you clearly indicated in talking about the intellectual atmosphere at the Seismo Lab and the things that were available to work on as a graduate student, today, for undergraduates and graduates interested in seismology, what's the low-hanging fruit for them? If not earthquake detection, what are the things they can work on that really are formative for the future of the field?

LANGSTON: Right now, there's a big bandwagon going on with machine learning. Maybe it's because I'm an old fogey now, but I'm skeptical. I think it's a good engineering tool to do some simple problems that we know about, but I'm not sure we're going to learn something fundamental. But I don't know. I always have to say I just don't know. The one thing I see in students in general, here and elsewhere, is that they're coming to rely on existing computer programs and algorithms they can get to do their research, and I don't see a lot of innovation, or another thing that worries me, a lot of appreciation for the background theory of why something works. Math requirements seem to have dropped over the years. It's hard to get students who really have a good math background and can very quickly come up to speed on theoretical concepts.

ZIERLER: I wonder if a lot of that is simply because we can outsource some of this work to computers.

LANGSTON: Yeah, but is that learning? I don't know. [Laugh] Are you learning something? I can tell, when I'm learning something, I figure out that I don't know something. Something doesn't look right. To get to the point to say that something doesn't look right, you've got to have some background vision of why it doesn't look right and some concrete reasons. Mathematical reasons, physical reasons why something doesn't look right. It's getting that background, which I think the students have to get before they can actually go and get the low-hanging fruit. Right now, it seems like the low-hanging fruit is to use a machine-learning algorithm to process 40 million seismograms to get an arrival time of something, get a location. To me, that's useful engineering, but it's not necessarily science.

ZIERLER: But if there's a breakthrough from machine learning, you'll be happy to be proven wrong.

LANGSTON: Oh, yeah. Absolutely. It used to be, when I was a grad student, I thought I knew everything. We'd have great arguments at the Lab. "It works this way." "No, it works that way." We'd argue back and forth. It was great fun. But ever since, and particularly now, I know that there's lots of stuff I don't know, and it's really tough to know anything.

ZIERLER: That's the way of science, right?

LANGSTON: Yeah.

ZIERLER: Chuck, this has been a great conversation. I'm so glad we were able to do this. I'd like to thank you so much.

LANGSTON: You're welcome.

[End]