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Hartmut Spetzler

Hartmut Spetzler

Professor of Geological Sciences, Emeritus, University of Colorado

By David Zierler, May 11, 2022

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Wednesday, May 11, 2022. I'm delighted to be here with Dr. Hartmut Spetzler. Hartmut, it's wonderful to be with you. Thank you for joining me today.

HARTMUT SPETZLER: You're welcome.

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

SPETZLER: Retired. Emeritus. [Laugh]

ZIERLER: From what program?

SPETZLER: From the Geophysics Program at the University of Colorado, which is a cooperative program between different academic departments and Institutes. I was a faculty member in the Department of Geological Sciences and a Fellow in the Cooperative Institute for Research in Environmental Sciences (CIRES), where I did my research. The graduate students in our group were mostly from Geological Sciences and Physics.

ZIERLER: You've published so widely in a variety of different kinds of publications on so much different subjects. What does that tell us about your overall approach to science?

SPETZLER: Well, that I'm interested in lots of stuff. [Laugh] For that same reason, since my retirement, I have quit doing research in science and I am finally catching up in the humanities. While still doing some research after 2003 I've been auditing a lot of courses with friends, e.g. history, religion, political science, philosophy, English and others. Since Covid we are taking courses using Zoom, lately on Dante's Inferno and right now we're looking at Greek and Roman mythologies and Egyptian History.

ZIERLER: From your publications, has geophysics and seismology always been your home base, so to speak?

SPETZLER: No. I'm a trained watch/instrument-maker from way back, and I fell into geophysics at Caltech as we were starting a family. At Caltech I was initially in physics and didn't want to travel from accelerator to accelerator looking for new particles, as was then in vogue. I had done that while in the Air Force when studying radiation effects for upcoming space travel. I came into geophysics and got into laboratory geophysics. There was relatively little seismology involved. My work before I came to Cal Tech was published in "Radiation Research (1962)", Proceedings of the IEEE (1963) and I believe others, which I do not recall. My continuing diverse interests while at Caltech and after are reflected in publications unusual for geophysicists, e.g. "Journal of Neurosurgery (1980"), "Physics Teacher", "National Geographics" etc.

ZIERLER: It's such a remarkable life story you have, coming from Europe to the United States. How did you get to Caltech? What were the circumstances of your arrival here?

SPETZLER: My curiosity and early inventiveness probably stems from playing in the rubble left in my home-town, Nuremberg, after WWII. It was a treasure chest for curious young boys. I had very understanding and tolerant parents allowing me to explore the world around me. In 1956 at age of 16 and after graduating from a technical school, I followed the rest of the family ( I am the oldest of 6 children) to the USA. Our father had been brain drained, i.e. lured to the USA because of his technical skills. I went to five different undergraduate schools, three of them simultaneously. The last one I went to was Trinity University in San Antonio, Texas. There, I met a mathematics professor, Prof. H. T. Davis, which is why I majored in mathematics through the master's degree. I had heard of Caltech and asked him about it. Upon his recommendation I accepted a job in Pasadena with the idea of going to Caltech. Then, in September of '63, I went to Caltech and told them that I would like to go to school there. The people at the little company I was working for, National Engineering Science Company (NESCO), were mostly Caltech graduates. They called the school and said, "Yeah, you should take him. At least he's good in the lab." [Laugh] I visited Caltech in September to apply, and was told: "Well, you can apply in January for next year." I said: "No, I thought of going to school this October." Caltech, in its flexibility, made it possible for me to start in the physics department in October. In my undergraduate work I had almost as many semester hours in physics as I had in mathematics. It was because of Prof. Davis that I majored in mathematics.

The way I honed my physics intuition was through the Feynman Lectures. I studied those and met on a weekly basis with Prof. Bob Leighton, who was a coauthor of the Feynman Lectures. If I ever got a feeling for physics, it was during that time. But then, when it came to research, it would've been a lot of looking for new particles at various accelerators. While I was in the Air Force I had worked at the School of Aerospace Medicine in San Antonio and did a lot of radiation research. This involved much travel to, I think, most of the large accelerators that existed at the time in the United States. I did not wish to travel so much anymore, instead support the family we had started. I discovered geophysics and met Prof. Gerry Wasserburg as my first contact. He was quite interesting and recognized my skills in multi-channel energy spectrum analyzers. I had worked with those instruments in the Air Force. He offered me a graduate research assistantship. I also worked with Prof. Lee Silver a little during this time. Prof. Orson Anderson came as a visiting Faculty member. He came from the Lamont-Doherty Laboratory of Columbia University, where he had started mineral physics. I was intrigued by the information which could be gleaned from ultrasonic measurements in the lab. I had found my interest in geophysics.

I went to Don Anderson and told him about my interest after I had read all the proceedings of the pertinent meetings. And it was actually Gerry Wasserburg who found the money for me to travel to every one of the geophysics labs I could find that were doing ultrasonics. These included industry as well as academic places, e.g. General Electric, Harvard and Brigham Young Universities, and many others. During these travels my interest was further focused and I was sure that I could make a significant contribution in material properties, relevant to Earth. At the time there was no ultrasonics at Caltech. I conferred with Prof Don Anderson while still on the East Coast and told him of my plans. He was interested in this research and I told him what it would take to build the appropriate laboratory. I needed to design and purchase electronic instruments as well as a pressure generating facility. I also mentioned that it was really too big of a job for one person to do, so I need a technician." Don Anderson was able to provide the finances for all of that. While I was still on this trip on the East Coast, I ordered the electronics for the ultrasonics, and I ordered the high-pressure generating equipment. We had to redesign all of it because I wanted to go to a high temperature at simultaneous high pressure. That was the big thing at the time in experimental geophysics.

ZIERLER: Why was Don Anderson interested at the time in supporting this research?

SPETZLER: He was not just a seismologist, he was an Earth scientist, who wanted to understand Earth's interior and its workings. For example, while I waited for the equipment that we had ordered, I did research on partial melting, because he was interested in the low-velocity zone. We used salt-ice as an analogue, a study that is still often referred to today. The ultrasonic measurements at high pressure and high temperature provided input to equation of state theories, which allowed us to better understand the composition of Earth's interior. With my skills as a trained instrument-maker and electronics technician from the Air Force, I was sort of the ideal super technician to develop a new lab and make the measurements. That's how we got started.

ZIERLER: What was your skillset coming out of the Air Force? What did you learn there that was relevant for this research?

SPETZLER: It was the time when the military draft was on, and I had been trained in Germany as an instrument-maker, watchmaker. I was good at designing and building mechanical things, which I used-and further developed- while I was working part-time at a chemical factory during High School and Junior College. I knew relatively little about electronics. I had heard that the Navy and Air Force had the best electronics schools, and at the time. For those branches one had to sign up for four years first, then one took tests, then the military decided where to send you. I signed up for the four years in the Air Force, and then I nearly flunked all tests except for the aptitude in electronics. They had but little choice to send me to electronics school in Biloxi, Mississippi. I got to experience the South in the 50s, which was very interesting, especially when we went off-base; separate drinking fountains, toilets, etc. I learned electronics in the Air Force and for nearly three years worked at the School of Aerospace Medicine at Brooks Air Force Base in San Antonio, Texas. There I worked in Radiobiology and learned about radiation physics and chemistry. I helped to install and then manage a 12,000 curie Co60 facility and worked with much diverse instrumentation. We sent many specimens through the radiation belts. The latter were generally caught over the Pacific and returned to us for analysis. I designed, prepared and built a spectrometer to distinguish between different radiation in the Van Allen Belts. The spectrometer passed all tests, including severe vibrations, and was mounted atop of a rocket as part of its payload. Thirty seconds into the flight the rocket veered off course and was destroyed. Sadly a monkey lost its life and 8 months of my hard work was lost as well. It was at this point in my life that I decided that I would not do a PhD theses, which would have to rely on rockets working.

ZIERLER: What were the science objectives at Caltech after you got this up and running with Don Anderson's support?

SPETZLER: Well, the science objective was to understand Earth's interior in terms of its composition and the states of the matter. This requires geophysical observations, e.g. seismology, gravity, magnetism etc. and thermodynamic laboratory data under conditions close to those that exist within Earth. Since not all relevant measurements can be made under conditions existing within Earth, there are many "Theoretical Equations of State" that beg for input data, which are then extrapolated.

ZIERLER: What were some of the prevailing ideas or theories at the time?

SPETZLER: There were many competing models for Earth's (also the planets) structure and its chemical composition based on the compositions of various types of meteorites, as well as the data mentioned above, and of course the laboratory data to anchor the models. It has been over two decades since I have worked on Equation of State matters and am not familiar with the present ones.

ZIERLER: What were some of the technical challenges in this experiment?

SPETZLER: Essentially, to push the state of the art of the measurements. At the time, there had been no acoustic measurements on partial-melts when we did the salt ice experiment. And as for the high-pressure-temperature experiments, if you drew, say, temperature on a vertical axis and pressure on the horizontal axis, there were some data along the pressure axis at room temperature. There were also some measurements on the temperature axis at room pressure. My contribution was to develop the technology to make these measurements at simultaneously high temperature and high pressure and to make sense of them.

ZIERLER: What were some of the findings from the experiment? What did you learn as a result?

SPETZLER: We measured thermodynamic properties of Earth materials or analogues under conditions of simultaneous high pressure and temperature. These data were the fundamental basis for "Equations of State", which were used to interpret geophysical data to explore Earth's and planetary interiors.

ZIERLER: How did this experiment fit into some of the bigger questions that were being pursued at the Seismo Lab at this point?

SPETZLER: At the time plate tectonics was first taken seriously and there was emerging hope for predicting Earthquakes. Seismic data provided the bulk of the measurements to steadily refine Earth internal structure. To interpret these structures in terms of their physical and compositional properties required knowledge of material properties, both static and dynamic. Our data and those of other labs provided the input for the necessary theoretical equations of state. It was a time when Charles Richter was still active and many historic Earthquake records were available to aid in the studies of predicting them.

An aside: I was present when in the 1960s a new Earthquake record was shown to Dr. Richter. He mentioned that it looked very similar to an Earthquake in the Indonesian Islands that occurred there in the 1930ties. Once it was located, its epicenter was indeed in those islands; an astonishing memory, especially considering that many Earthquakes were recorded every day.

ZIERLER: How does convection happen? What were some of the ideas at that point? How did you contribute to them?

SPETZLER: If you study convection, you need to know the physical properties of the material to determine, for example, whether the geothermal gradient is adiabatic or super-adiabatic. It needs to be steeper than adiabat to make convection even possible. Without the physical properties as inputs to the mechanistic models the study of convection would have remained a geometric puzzle.

ZIERLER: Was this project similar to what other graduate students were doing at the time? Were you off on your own? Or was there a bigger collaboration that you were a part of?

SPETZLER: No, I was sort of off on my own.

ZIERLER: What does that tell us about the kinds of questions you were pursuing at that point?

SPETZLER: I don't know how to answer that very well other than the fact that they were, experimentally, very challenging, and people were asking for the answers. It was through the emergence of plate tectonics that it became especially important to learn about the properties of Earth materials at simultaneous high pressure and high temperature. Prof. Don Anderson recognized that need and supported my efforts through scientific guidance and financially. Shortly after I had started the ultrasonic equation of state work Dr. Thomas Ahrens joined the faculty and established a shockwave facility. The data from both facilities complemented each other in providing equation of state data.

My education as an instrument maker in Germany and as an electronic technician in the US Air Force gave me a unique background which helped tremendously in establishing a new facility. When I moved to the University of Colorado, after having been at Sandia for a few years, Caltech actually let me have the laboratory, and it was sent to Colorado. It went back to Caltech after a few more years, being still close to the state of the art. While I was a graduate student at Caltech a number of visiting scientists came and worked for several months to a year in the new lab, e.g. Edward Schreiber from Lamont-Doherty, Hideyuki Fujisawa from the University of Tokyo, Richard O'Connell before he left Caltech to go to Harvard

ZIERLER: Were computers part of your graduate research?

SPETZLER: I used them, yes. It was the time of the cards for the big IBM machines. To interpret the experimental data I had to solve many simultaneous differential equations. Thomas Jordan, an undergraduate student at the time, helped me with the programming and handled the big boxes of computer cards. We also used small computers in the lab; Wang was the name of at least one.

ZIERLER: Did you do any field work for your graduate research?

SPETZLER: No. Although another graduate student, Steve Wolf, and I, under the guidance and sponsorship of Prof. Eugene Shoemaker, did a 6 week geologic investigation of the Manicougan Impact crater in Quebec. This was for later astronaut training.

ZIERLER: Where was the data coming from? What was most important to you at that point?

SPETZLER: From the measurements in the lab. We made measurements within a high-pressure vessel with an internal furnace. I was pushing the state of the art and was able to provide data in the pressure-temperature space that were heretofore not possible.

ZIERLER: Just to clarify, this was strictly a lab-experiment thesis. There was no field data.

SPETZLER: Correct.

ZIERLER: How do you simulate the situation in a lab so that you can extrapolate those findings for what happens in the real world?

SPETZLER: The temperatures and pressures we could reach in the lab were only equivalent to those of a few kilometers' depth. Theoretical equations of state were needed to extrapolate the data to the deep Earth interior. For the first time we were able to provide not only pressure and temperature derivatives but also their respective pressure and temperature dependences, e.g. how the pressure (P) derivative of velocity (v) varied with pressure (P) as well as with temperature (T), dv/dT, dv/dP, d2v/dP2, d2v/dT2, d2v/dTdP. The bigger the datasets are and especially the more accurate, the better the theories become. And then, you apply them to the seismic data that come from the seismologists.

One of the questions, of course, is that seismic data have much longer wavelength than we have in the laboratory. Various arguments and rationalizations are used to find the lab data useful. As the experimentally possible pressures have increased the sample sizes have of course decreased as well. Using guidance from acoustic microscopy we have introduced ultrasonic at GHz frequencies in a Diamond Anvil Cell. Those frequencies generate wavelengths equal to those in the optical near infrared. The successful extrapolation from GHz to lower frequencies (MHz), by several orders of magnitude, gives us added confidence that laboratory measurements are applicable also to longer wavelengths as in Earth.

To further check scalability between lab and reality we had an experiment going that was on actual rocks. In our lab we were restricted to rock samples measuring in the cm range. In the early 1980ties with Soviet colleagues we did an experiment in Russia on a rock sample that was almost two meters tall. A 50,000 (50,000 VW Beatles stacked) ton press was made available to us. It was the largest press, available in the world, for research at the time. We were investigating the strength and manner of failure of rock samples as functions of size. It was a fantastic time not only for the science, but also for the cultural aspects. For example, we had to ignore large concrete samples that were used for missile siloes and were tested for their strengths in this huge press.

ZIERLER: Was Don Anderson your thesis advisor?


ZIERLER: How closely did you work with him?

SPETZLER: That's hard to say. On what I would call the first part of the thesis, it was rather close. It was the work on sending sound waves through a partial melt and measuring their velocity and attenuation. He was very interested in that. And on the major part itself, he wasn't able to help me experimentally. He was very much interested in the data. I'd generate the data, and he used it in his interpretation of Earth, along with any other data that existed. I didn't spend many hours with him, working in the lab. I was essentially alone working closely with the technician and friend David Newbigging.

We had built a hydrogen furnace, a furnace that you stream hydrogen through. The hydrogen gets burned off at an opening at the front of the furnace. It's a little tricky to light it. If you light it too late, the whole room blows up. If you light it too early, there's too much oxygen in the furnace's interior and the furnace blows up. For safety, the furnace was behind a concrete pillar. On a rare occasion when Don Anderson was visiting the lab, and I had just lit a match on the end of a coat hanger and was about to use a mirror so I could light the furnace behind the concrete pillar. Once the hydrogen was flowing the hydrogen curtain had to be lit. I lit it a little early because of being distracted. And it made quite a poof. I think that was the last time Don came to the lab. [Laugh]

ZIERLER: [Laugh] Well, you're still here, so it couldn't have been too bad.

SPETZLER: No, it was okay. We were careful.

ZIERLER: As you mentioned earlier, this data was important for refining the theories, for pushing the theoretical advances. In what ways? I wonder if you could explain a little more in detail.

SPETZLER: My history isn't that good, but the way we imagined Earth before seismology was a big ball. We didn't know much of the structure of Earth. Then, through seismology, we got the inner core, the outer core, the mantle, and the crust, then later, the low-velocity zone, which was sort of a miracle. A bunch of rather scattered points on a plot, and Prof. Gutenberg drew a curve through them. Over the next 50 years, as data improved, the points came ever closer to the original curve he had drawn. The interaction between theorists and experimentalists, providing the data, lead to better understanding of Earth's structure and its chemical composition. There's no particular aspect where I can say, "This experiment solved any particular geophysical problem."

ZIERLER: How involved were you more generally at Caltech beyond the Seismo Lab with planetary science in GPS?

SPETZLER: I started in Mudd with Professor Wasserburg. Steve Wolfe, another graduate student, and I approached Prof. Gene Schumacher after we took a course from him in planetary science and asked how we could contribute. He sent us to Manicouagan, in Northern Quebec, close to the Hudson Bay. There is a meteor impact structure. The Canadians, at that point, still thought it was a crypto volcanic explosion. We were there for six weeks, and did a field study. We brought some minerals back, the identification of which stumped Professors Leon Silver as well as Hugh Taylor in terms of what they were. They turned out to be felspar glass produced by the shock. I also helped Professor Clair Patterson on his lead studies. He came to me and wanted to know how much ore, containing lead, was mined in Germany during the previous centuries all the way back including Roman times. He brought old publications, and I read through them and tried to extract information on lead. He was interested in lead contamination and how it might have impacted the Roman elite.

ZIERLER: Besides Don Anderson, who else was on your thesis committee?

SPETZLER: Gerry Wasserburg. Probably Tom Ahrens. Maybe Charles Archambeau from the theoretical side. Another seismologist. I don't remember for sure.

ZIERLER: What would you say the key conclusions of your thesis were?

SPETZLER: There was no big scientific conclusion. I have answered above what doors were opened through the new data I had generated. There was one thing from the partial melt data that intrigued me very much but didn't seem to excite anybody else as much. We had measured seismic absorption through the phase change in salt ice and it was quite frequency-dependent. At first, we thought only of physical mechanisms and could not find a good reason for the frequency dependence. Upon more thought I discovered that it was due to a chemical reaction. I was intrigued by the idea of driving chemical reactions across phase changes with acoustic waves and that we were in the right frequency range to study that. I didn't follow that up and stayed with the equation of state and the strength of materials.

ZIERLER: Was this research relevant at all for industrial or commercial applications?

SPETZLER: Not really, except in the advancement in the state of the art of equation of state measurements. At one point, I did go to Hewlett-Packard and suggest that they could make a simple pressure sensor that would be very sensitive at ocean depths, etc. They told me that they had used a different technique, and were quite happy with the one they had already developed. They showed me their tsunami predictors that they had scattered under the oceans. When the average water depth increases by half a meter or so out in the oceans, it is the sign of a big tsunami.

ZIERLER: Your innovations with ultrasonic measurements, have they been adopted for other experiments?

SPETZLER: Well, yes and no. In a sense, ultrasonic interferometry is a relatively big field now. I found copies of my theses in several laboratories.

ZIERLER: After you defended, what opportunities were available to you? Did you want to look for post-docs first?

SPETZLER: The year I graduated every other students went to a faculty position. I felt rather strongly that teaching was an important aspect of being a professor, and somebody who had gone from kindergarten to PhD and had never been outside the academic environment lacked somewhat in general experience to be a teacher. I wanted to go out into the real world for a while, so I traveled to many different non-academic research facilities and had many offers.

This was shortly before the first lunar landing and the expected arrival of rock samples from the Moon. There were contamination problems at NASA's lunar receiving laboratory and I was encouraged to apply to direct the lab, not because of my equation-of-state work, but because of my technical skills, including those of plumbing. Prof. Wasserburg felt strongly that I should help in that position. NASA and I could not agree on the conditions under which I was willing to take the job and I was also looking for a location for our family with better weather. Later I served on several NASA committees dealing with Lunar material. I had Lunar rocks in our lab for research and took NASA-prepared Lunar samples to various schools.

Partially because of location and partially because of, once again, the chance to build a laboratory from scratch, I joined Sandia Labs in Livermore. I was there for five years and insisted on doing good and academically interesting work. I kept going to AGU and other meetings and was approached by SUNY Binghamton to go and teach there. I took a leave of absence from Sandia and taught at Binghamton where they promoted me after one semester to associate professor and said, "You can resign, but we'll keep the position open and hope that you'll come back." I told them there was no guarantee I would come back and took a leave of absence from there also. On our way back from New York to California, we stopped at the University of Colorado. Because of the kind of experiments (optical holography) I did, I interviewed with Electrical Engineering, Physics, and Geological Sciences. I got happily stuck in Colorado for nearly 50 years. I had joined the faculty of Geological Sciences and CIRES. Geologists in general get along better than people who are only in the lab or behind the desk. When frustrated, geologists take their geology picks, go out and crack a few rocks. [Laugh]

ZIERLER: To go back to Sandia, what was happening there that was relevant for your research, your area of expertise?

SPETZLER: They were interested in equations of state under high temperature and high pressure for nuclear-blast containment underground and whatnot. The branch of Sandia in Livermore was relatively new. They had hired a whole bunch of new PhDs to start a research program. Previously I had interviewed with Sandia in Albuquerque, which is a much bigger place than Sandia in Livermore. I had known some people there who were working on equations of state of various geologic materials and metals. Shortly after I arrived in Livermore, I wrote a proposal to initiate research in equation of stat work that would complement the work going on in Albuquerque. They weren't used to proposals and were a little surprised. I sent the proposal to appropriate scientists in Albuquerque. They thought the proposed work would complement the work there and gave it a supportive review. I got the money, found a building in which to build another high-pressure lab, which was better and more sophisticated than the previous one at Caltech. We measured equations of state of salt, zinc, mercury, bismuth through the melting point. We wanted to know the thermal expansion of materials as well.

A scientist from Rice University gave a talk at Sandia. He used electromagnetic levitation of aluminum. They'd get it hot, measure the temperature with an infrared detector, then drop it into a calorimeter to measure the heat capacity. About the same time, on the cover page of Science was a picture of a doubly exposed hologram of a defective automobile tire. It showed a bulge that was not visible otherwise. I put the two things together and figured that we might be able to levitate liquid aluminum and measure its thermal expansion with optical holography. We set up a lab to do exactly that and were successful. It was quite a lot of fun.

ZIERLER: How would you characterize the quality of instrumentation available to you at Sandia?

SPETZLER: It was fantastic. They were very well equipped and well-funded. Since I knew what I wanted and needed, they were somewhat surprised and funds became available quickly. Most of the other young PhDs asked, "What do you want me to do?" I arrived and said, "This is what I should do in order to solve some of your problems." I also found a perfect building to set up the high pressure facility. The building had just been vacated and was to have housed a Co60 facility. The walls between the large hall and the instrument rooms were thick and safe, not only appropriate for radiation shielding, but also for blast protection

ZIERLER: Was any of your work at Sandia classified?

SPETZLER: Very little. I participated in a couple of brainstorming sessions that were classified. As luck would have it, our building was located at the periphery of the Sandia property and since our research was not classified we could arrange the fence so that our building was mostly not in a restricted area, which meant that visiting academic people and summer help didn't have to go through the extensive clearance efforts to work with me. I was very fortunate and received many visitors from domestic and foreign academic institutions. That may also be part of the reason it was easy to get back into academia.

ZIERLER: Were you happy at Sandia? Could you have spent your career there?

SPETZLER: That's a tough question. Partially so because, in addition to my equation of state work, I was involved in a number of other projects that were lots of fun; e.g. underground coal gasification near Hanna Wyoming, design and tests of aspects of parachutes. Sandia was branching out at the time and getting involved in non-weapon programs.

Additionally, I was concerned about my role in the military-industrial complex. President Eisenhower had warned us of its possible evils. While I believed in a strong defensive military, I was worried about industry needing and influencing the military. Our vice president had gone to Washington to some appropriations meeting. He came back quite happy and said: "Congress approved it, we won." It was the approval of a missile system, which was to provide partial funding for Sandia. At the time I was reading "Inside The Third Reich", a book by Albert Speer, Hitler's Architect and later the Minister of Armaments and War Production in the Third Reich in Germany, the country of my birth. As I recall, early in the book he describes the irresistible opportunities he had as a young man to design and lead huge projects. He claimed not to have asked the important questions of the overall purpose, ethics and motivation that formed the foundation for these incredible opportunities.

I did not wish to fall into the hole that sucked Albert Speer in and wondered why our vice president was convinced we needed another missile system. Was it in order for the United States to be safe, then I would agree with it. And if he said, "we won," because he had more money to pay his people and be the father figure that takes care of his people, then I wasn't okay with it.

Now that I am in my eighties, I ask myself whether I used this episode to escape the military-industrial complex or if it was the chance to work with young bright people, teach and do research in an academic setting that attracted me to academia. In any case I very much enjoyed my career and am not at all sorry for my decision.

ZIERLER: What was the initial point of contact that got you that interview at Colorado?

SPETZLER: I kept attending meetings and presenting papers on my work at Sandia. Often I would carry a small He-Ne laser and complement my presentation with showing holographic images either in the lecture room or later in hotel rooms. Prof, Carl Kisslinger was director of the newly established institute CIRES (Cooperative Institute for Research in Environmental Sciences). He and others knew of my work and asked me to visit. Since CIRES is a cooperative institute, it involves many departments and governmental units, especially NOAA. Through its cooperative nature it provides much flexibility and many opportunities.

ZIERLER: What department did you eventually join? You were interviewing widely. You talked to a lot of people at Colorado. Where did you land?

SPETZLER: My position was through CIRES. I ended up in the Department of Geological Sciences rather than in Electrical Engineering or Physics.

ZIERLER: By virtue of being affiliated with this program, in what ways did that change your research, the kinds of questions you were focusing on?

SPETZLER: The opportunities seemed endless and the variety of research going on was overwhelming. At this time there was still great hope of learning to predict Earthquakes. My group got involved in studying failure mechanisms in rocks. Toward that end we built a pressure vessel with two orthogonal sets of pistons and a very thick glass window. This enabled us to put heavily-instrumented rocks under true triaxial stress and observe the failure side, which we did while taking holograms. We were thus able to observe the surface deformation as internal cracks were coalescing leading to eventual failure.

Moisture plays an important role in creep and failure of rocks. In trying to understand this moisture effect we were looking for very dry rocks as one extreme. This lead to the study of Lunar rocks. Since rocks are very complicated and fail by the coalescence of microcracks, we needed to understand single cracks. We became aware quickly that the surface tension between rock surface and liquid in a partially saturated rock plays a major role in addition to e.g. the crack geometry and connectivity, viscosity of the fluid etc. We designed and built equipment to measure moduli and their attenuation on rock samples and single cracks in the seismic frequency range.

To study scattering of acoustic waves from single cracks we built and calibrated a seismometer that worked in the megahertz range. In collaboration with Prof. Robert Sani from Chemical Engineering we studied the scattering of Lamb waves from a single crack; a precursor for a possible instrument for early detection of small cracks.

There are many more examples, e.g. the use of a Seismic Vibrator (huge truck) for time dependent studies of fluid movement below ground, archeological study of a Mayan area in El Salvador covered by volcanic ash, deformation of the human skull due to simulated blood flow through tumors, using Earth tides to study time dependent changes due to contaminant fluid flow underground, and others.

CIRES provided a structure for doing research, excellent support in terms of administration, research opportunities and space, but especially the exposure to many fascinating scientists and visitors. In the late 1980ties CIRES got a new building on campus. We were doing very acoustic noise sensitive Q (Sound attenuation) measurements at the time and were able to get a pillar going all the way down to bedrock that was insulated from the rest of the building. Geological sciences provided mainly a platform for teaching and a wider interaction with colleagues. I served as chair for in the department of geological sciences and thus had two good homes at the university of Colorado.

ZIERLER: To go back to an earlier question about the eclectic nature of your research, at what point did that happen for you? When did you start to take on new areas of interest?

SPETZLER: Much of your question I have answered in the previous paragraph. Here is a little more detail on some of that. It was because of our intrigue with holography that one of my brothers, Robert, a famous neurosurgeon, and I did experiments on the skull to see how the skull was deforming. The question we posed: would the skull deform enough during a heartbeat that we could detect a small tumor on the inside. To simulate the condition a human skull was filled with salt, and we had a little balloon filled with water on the inside. We would inject a little extra water to simulate a heartbeat to see how the skull deformed. Similar to the automobile tire, the skull showed a small bulge easily detected with double exposure holography.

The Mayan study involvement began when Prof. Payson Sheets showed up in my lab with three bags of sand, asking whether I could tell the difference between the different materials. I said, "Yeah, sure, this one is that color, this one is that color." He is an anthropologist. We went to El Salvador. I borrowed a ground penetrating radar unit from Prof. Gary Oelhoft at the Colorado School of Mines. We mounted it on an ox cart to avoid reflections from metals and pulled it back and forth on a grid. We also used electrical resistivity and simple seismic means to look for buried Mayan structures. It was a fascinating opportunity to do something out of the lab and in a different field. Today, when political stability allows it, the structures are visitable at: Joya de Ceren Archaeological Site in El Salvador.

ZIERLER: What were some of the key advances in instrumentation that allowed you to expand your research agenda?

SPETZLER: When I built the lab at Caltech, we did some innovative things that had not been done before, which allowed us to go to high pressure at simultaneous high temperature. Often these advances were rather subtle. For example, instead of using glues, which are very temperature limited, to acoustically couple to the sample, we learned to prepare high grade optical flats for acoustic coupling and were able to eliminate any glue, thus the high temperatures. We designed three stage furnaces with separate power control of each stage. This was necessary to eliminate convection and therefore large temperature gradients within the furnace. We added a little radioactive Krypton to the pressure medium, Argon gas, and could find very small leaks with a Geiger counter.

In 1986 the Bavarian Geoinstitute (Bayerisches Geoinstitut) was built in Bayreuth (close to my hometown of Nuremberg), Germany. I was asked to join and be director for a few years. After some struggle, my wife and I finally decided not to move to the area, which I had left 30 years earlier as a teenager to immigrate to the USA. Also, the University of Colorado wished to retain me. I had just finished being chair of Geological Sciences and needed to reenergize our research. The University, partially through CIRES and the Department, offered a retention package similar to a new hire. This included some discretionary funding as well as support for new research. My relationship with the Bavarian Institute remained very close. I collaborated with scientists from there and spent several sabbatical years there, some sponsored by the Alexander von Humboldt Foundation. Colorado was just too nice to leave and all of my immediate family including our children, are in the USA.

Ivan C. Getting, who has been working with me for over a quarter-century, and I sat together and ask ourselves the question, "If we were to start over, what would we do?" We had drifted away from ultrasonics at high pressure and temperature and embraced crustal problems which involved the behavior of rocks at crustal conditions. We studied the effects of moisture and contaminants on strength, creep and seismic attenuation of rocks, single cracks and also single crystals

To answer our question we searched for geologic problems that required experimental input and where we had some competence. Equation of state measurements were near the top of the list. At the time I heard an intriguing seminar on ultrasonic microscopy. I had no idea one could generate sound waves at several gigahertz and immediately thought of ultrasonic interferometry. With the funding from the University of Colorado and NSF Ivan and I were able to start a new field again; GHz acoustic interferometry. I visited various labs engaged in ultrasonic microscopy to learn some of their techniques. In Colorado we built the first GHz ultrasonics lab and at Bayreuth we first adapted ultrasonics to a diamond anvil cell. We used internal reflections within a single crystal to convert P waves to S waves and thus were able measure all elastic constants in a sample. We had lots of fun extending the frequency range by several orders of magnitude and in the process reducing the required sample size similarly.

ZIERLER: What would you say some of your most significant findings were in lunar research, both in terms of understanding the moon and understanding the earth?

SPETZLER: Lunar anorthite covers a lot of the lunar surface. It is a very porous material due to all the bombardment by meteorites. The major contribution of our measurements were in the relationship between the moisture content and the physical properties of the rocks, e.g. sound velocities, creep, strength etc. Lunar rocks formed the dry endmembers for the moisture content of our studies. Out of that came a whole series of studies on the effect of moisture on the properties of rocks, where we'd evacuate them to very high vacuums, bake them and then put moisture back in to see how their properties changed.

ZIERLER: Besides the moon, what other planets have you looked at when you've concentrated on crustal strength?

SPETZLER: We looked at the rocky ones in our solar system. We looked at our data, mimicked the boundary conditions we would expect on the planetary crusts, and then calculated the highest mountains that could exist on Earth, Mars, Venus. I don't think we did much with Mercury. The heights of the mountains, for example, depend on the climate. Rocks behave quite differently under moist conditions than under dry conditions.

ZIERLER: Where else have you seen holographic interferometry been applied?

SPETZLER: We wrote a book on holographic studies. We used it on material strength inside a pressure vessel as well as outside. It was used with ruby lasers to check the deformation of large antennas at TRW at the time. Ruby lasers have a much longer coherence length than the helium-neon lasers, which we usually used. By taking a hologram of a big antenna, and then making a second exposure at a slightly different temperature, you can see its distortion, and that's important in microwave technology. I visited an engineer in Germany who was working in his garage for BMW. He used holography on the frames of automobiles. He would set the frames into vibration, see where they vibrated most, then put certain weights on various places to shift the frequency so you wouldn't feel it. Holography can be a general tool with a lot of applications. I don't know where it is used in industry.

ZIERLER: Where do you see some of your contributions looking at rock failure as they relate to trying to predict earthquakes?

SPETZLER: I was probably still at Caltech when Prof. Frank Press came to Caltech for a meeting, and that's when earthquake prediction really started. In retrospect our efforts were a big failure. We don't know how to predict earthquakes. I remember an occasion when Prof. Don Anderson showed a map where radon came out of the ground, where strain was observed, where small earthquakes happened. There was very little temporal or spatial correlation to where a big might occur. What it has contributed, though, is to laboratory experiments, to gain a better understanding of the strength of the rocks and the processes by which they fail. Instead of being able to predict Earthquakes long before they occur, Seismologists in California have an early-warning system, which allows them, once an Earthquake occurs, to take actions, e.g. close valves, shut off electric power. This general research thus greatly helped in Earthquake mitigation and also in the monitoring of nuclear test ban treaties. We still don't know how to reliably predict earthquakes. I don't think anyone knows.

ZIERLER: What about your work on submillimeter crystals? What were you looking at with that?

SPETZLER: At equation of state properties at ever deeper conditions in Earth. One time, we had water in a diamond anvil cell, and observed the properties of ice at different phases. Some of the phases are solid ice at room temperature after they have been pressurized in a diamond cell. One big surprise: when we looked at how the acoustic interference patterns were changing with time, we thought we were measuring the equation of state of the ice, but what we were actually measuring was the growth of the interface between a single crystal of ice and the water. And that was a lot of fun, especially since we were able to also observe it optically.

ZIERLER: On the teaching side, tell me about your involvement with the EarthWorks program.

SPETZLER: The main reason for my return to the academic life was my interest in teaching at all levels. I put special emphasis on non-science major courses because it is there that we have the greatest influence on the scientific literacy of the public; maybe I had some positive influence, but as national educators we have failed miserably. To better understand the process of education I visited and taught, as a substitute teacher and a volunteer for almost two decades, in grade, middle and high schools after my retirement. As a faculty member I was involved in the outreach program of CIRES and as part of that became involved in EarthWorks. It was a program for high school teachers that would come to Colorado for a summer course, three or four weeks, and go out into the field to engage in some research. University faculty members who would guide and work with them. It seemed like a good program, helping the faculty members learn to better communicate with the teachers and the latter to get an appreciation of where data come from. I'm still in touch with a few people who participated in that. It was 30 years ago, maybe.

ZIERLER: More generally, through CIRES, what has been your involvement in looking at how scientists and educators can interact productively?

SPETZLER: That's a tough question because if you look at our politicians, you can tell them about data all you want and show them trends, and they don't react to it. There's a lot of research going on right now in how to communicate science. Where I made my biggest contribution probably was putting quite a bit of work into non-science major courses and making them interesting, not caring so much about how much science and facts they learned, but how they appreciated science, and the approach of science, and what kind of questions we ask. For example, I would give them a homework to take some geologic feature, from a planet or a little pebble, and first, describe it, then speculate how it may have formed and finally formulate significant questions about it. We would then discuss these things in groups. I had a lot of fun teaching non-science major courses.

ZIERLER: Moving closer to the present, when you retired and could focus on whatever you wanted, what was the science that was most interesting to you?

SPETZLER: I guess genetics and the brain; how it functions? I try to keep up with science in general at the level of the occasional Scientific American article, Time Magazine, etc. I enjoyed doing science, discovering little bitty things nobody knew before my group discovered them and thus contributing small parts to human knowledge. I had ignored most of human knowledge until my retirement and since then have become interested in religion, philosophy, history, even political science, which I still consider an oxymoron.

ZIERLER: You're making up for lost time now.

SPETZLER: Yeah. I have taken a lot of in-person courses at the university, and since the pandemic, Zoom courses, which are quite nice in the sense that, if you take one with a few people, you can stop it, you can reverse it, and you can listen to it again, which is a little more difficult in the classroom.

ZIERLER: In the way that you've sacrificed to be so focused in your science over your career, what are you most proud of in terms of your contributions, what you were able to discover?

SPETZLER: It's hard to say. I think it's the wide spread of students I have been able to interact with and what they have carried on. There isn't a single little thing that I would mention that has been an Earth-shaking kind of discovery.

ZIERLER: What are some of the things you learned at the Seismo Lab, your approach to the science, the way to set up an experiment, that have stayed close to you ever since?

SPETZLER: I guess it's to look for and find opportunities. Nobody told me, "Here's a problem that's interesting for you to work on." Everything I have done has been sort of as a self-starter. What was so neat about the Seismo Lab is that there were all smart and enthusiastic people. Twice a day we, faculty, staff and students, would have coffee under rather primitive conditions in the heating and storage area. I don't think a paper has ever been written during the years I was there that wasn't started there or at least discussed there. It was a fantastic time.

ZIERLER: For my last question, I'd like to flip the concept of discovery on its head. Looking to the future, what are the big, remaining open questions in the field that have yet to be discovered that you might suggest young scholars focus on?

SPETZLER: In the area of teaching I would like to see discoveries that contribute to a better general scientific literacy and critical thinking, an ability for the population to distinguish between conspiracy theory and scientific theory. On the applied side geophysics can of course make big contributions for the solving of societal problems, e.g. water quality and abundance, energy supply, the whole climate question etc.

In scientific research the whole idea of genetics is fantastic to me, how all of that works, how we can splice genes, how we can modify them, etc. The manifold applications are nearly endless, e.g. in plants, animals and also humans. In terms of geophysics, I'm not up with the latest research, but in the broader sense, to understand the climate is certainly an important aspect of Earth and planetary sciences. And there, looking at some of the planetary atmospheres may not be a waste of time. The same physical laws supposedly hold. I don't think we have found them to be different yet throughout the universe. We find some extreme conditions, especially on Venus and Mars, the study of which might help us to better understand our own. I think planetary science and space exploration are still fascinating and should be pursued. The moons of Jupiter, I could easily be persuaded to be involved in some experimental project to get through the ices of Callisto, Europa or Ganymede, maybe.

ZIERLER: Who knows what's underneath? It's exciting to think about.


ZIERLER: On that note, Hartmut, it's been a great pleasure spending this time with you. Thank you so much for doing this. I really appreciate it.

SPETZLER: You're welcome.