Susan Hough, Geophysicist

Between Caltech's Seismo Lab and the United States Geological Survey field office nearby, Pasadena, California can claim to be one of the world's foremost centers of seismological research. Susan Hough, a research geophysicist at the USGS, has a doubly rich perspective on the relationship between the two institutions: as a leading seismologist in the areas of ground motion, induced earthquakes, and earthquake interactions, Hough has maintained important collaborations with Caltech colleagues over the years. And as an accomplished historian of seismology - something she fell into as she came to appreciate the historical context of the science - she is well positioned to reflect on how the Seismo Lab has shaped the field in its 100 year history.

Hough completed her graduate research at the Scripps Institution of Oceanography, and her service work includes past membership to the Board of Directors at the Seismological Society of America and the Southern California Earthquake Center. In addition to her scholarly publications, Hough has published several popular books on the history of seismology. They include: Predicting the Unpredictable: The Tumultuous Science of Earthquake Prediction (2009); Richter's Scale: Measure of an Earthquake, Measure of a Man (2007); and The Great Quake Debate: The Crusader, the Skeptic, and the Rise of Modern Seismology (2020).

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, May 2nd, 2022. I am delighted to be here with Dr. Susan Hough. Sue, it's great to be with you. Thank you for joining me today.

SUSAN HOUGH: I'm really looking forward to talking to you.

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

HOUGH: I am formally a Research Geophysicist with the US Geological Survey in Pasadena. That is, my governmental job classification is geophysicist. I'm essentially a seismologist. I've been in Pasadena since 1992, almost exactly 30 years.

Partnership with the Seismo Lab

ZIERLER: Sue, let's start first on the institutional side. What are the connections, both formally and informally, between USGS in Pasadena and Caltech Seismo Lab?

HOUGH: I'm sure you've covered this ground. But this coordination is integral to USGS operations in Pasadena. Caltech was in Southern California, running a seismic network going back to the 1920s. The US Geological Survey was not in the earthquake-monitoring business for most of that time. There were governmental agencies that installed specialized strong-motion instruments to record big earthquakes, going back to the 1930s. But seismic networks were really run by universities. Then in 1977, the government launched the first ever federal program aimed at risk reduction, so the NEHRP, National Earthquake Hazard Reduction Program. It really should've been called risk-reduction program. But at that point, the USGS became the lead agency within NEHRP for seismic monitoring. That's when the USGS got into the earthquake-monitoring business. You're getting the long answer.

ZIERLER: No, that's great.

HOUGH: In California, when NEHRP was launched there were two existing seismic networks, one operated by Berkeley in Northern California, and the one operated by Caltech in Southern California. The state is split diagonally [laugh] sort of this way. People call it the Gutenberg-Byerly Discontinuity, jokingly, because Beno Gutenberg was in Southern California, Perry Byerly was in Northern California, and they sort of—I don't know—somehow agreed on which turf would be covered by which network. It really should be the Wood-Byerly Discontinuity because Harry Wood, not Gutenberg, was the driving force behind the seismic network in southern California. But, in any case, there were these two seismic networks that were both quite small—small numbers of instruments. When the USGS started to get involved with earthquake-monitoring, in Northern California they set up a group in Menlo Park, and they established a separate USGS network. That is, the USGS scientists in Northern California did not team up with Berkeley, so they ended up with two kind of parallel networks. It is a legacy that has reverberated through to the present. Whereas in Southern California—and I'm not sure who the folks were who were spearheading the USGS part of it, but from the start they worked in partnership with Caltech, running a seismic network that was then very much expanded with additional resources.

USGS-Caltech network operations began in the late '70s. At that point, the Pasadena office, its whole reason for existence was operating a seismic network in collaboration with Caltech. I joined the office in '92. At that time, all of the scientists in the office had been focused on what we call network seismology, looking at using seismic networks to record and study earthquakes, typically to locate them, determine the magnitudes, that kind of thing. I was hired to—boy, this gets into the weeds—to look at ground motions, so how strong does the ground shake when there's an earthquake? This kind of research used to be separate from network seismology: "strong motion" versus "weak motion" seismology, using different types of data to address different types of problems. When I was hired, I was the first person in Pasadena who, from the '70s, wasn't focused on classic network seismology. From the beginning through 1992, the USGS-Caltech collaboration had remained focused. Over time, the Pasadena office and the USGS has broadened its portfolio, so now there's a lot more going on than network seismology. Some of the USGS research is done in close coordination with the Seismo Lab. Some of it's more independent. But the network is still run as a joint project, and a lot of the research is still highly collaborative.

ZIERLER: I asked on the institutional side. For you personally, what are your professional connections, both formally and informally, with the Seismo Lab, just on a day-to-day level?

HOUGH: Formally, it's changed over the years. At one point, they had adjunct faculty positions. I believe that's gone away. I honestly don't know. I think I'm an external affiliate or something. I don't pay too much [laugh] attention to sort of what my formal—

ZIERLER: Could you sit on thesis committees? Could you do that kind of thing if you wanted?

HOUGH: I have in the past. I've supervised postdocs. I've collaborated with faculty and researchers. It's very collaborative, sort of organically so. You might start working on something, and realize that someone's interested in it, and collaborations develop.

ZIERLER: In terms of the overall mission, both of the USGS in Pasadena and the Seismo Lab, where is the overlap for collaboration, and where are there really different spheres of the mission where there might not be obvious opportunity to collaborate?

HOUGH: The USGS is focused very directly on understanding seismic hazard and reducing risk. The Seismo Lab has a broader focus, both research that is relevant to hazards and more "academic" research. For example, the Seismo Lab has long been interested in global seismology, that is using data from certain types of seismic instruments to kind of probe the structure of the whole Earth. It's sort of like CAT scan technology, using seismic waves to develop models for what's going on in the Earth. You can try to figure out the geodynamics. Research like this is not generally relevant for hazard, so USGS scientists aren't involved with that kind of work. Basically, the overlap is where seismology is relevant to seismic hazard.

ZIERLER: For your own scholarship from your educational trajectory, your graduate work, to your career, what have been the main areas of research you've focused on?

HOUGH: One has been what's called ground motion seismology, which involves looking at recorded seismic waves to understand how the ground shakes when an earthquake happens. Part of that is understanding how the waves propagate through the crust, and how shaking is modified by local geologic structure. That's been one focus. That dovetails with work that's been done traditionally at the Seismo Lab, developing methods to predict how the ground will shake based on computer models, for example. I've looked at historical earthquakes. I've looked at induced earthquakes, so earthquakes that are essentially caused by human forces of some kind. I've looked at how earthquakes interact with one another so, once you have an earthquake, how does that influence other faults, potentially, and sometimes trigger earthquakes? There's been a range of things.

Becoming a Historian of Seismology

ZIERLER: I want to get to the bigger question of how you became a prolific writer and historian in seismology.

HOUGH: [laugh]

ZIERLER: But to stay on the research side of things, has all of your research and all of your historical appreciation for the development of the field, has that influenced your work as a scientist at all?

HOUGH: It's hard to say where's the chicken and where's the egg. You start looking at historical earthquakes, and you very quickly get drawn into the historical aspect of earthquakes. What was going on at the time? What were scientists saying at the time? I think when I was in school, history was the one subject I actually didn't care for. I thought the way it was taught all the way through high school was just so dead dull. [laugh] Memorize these dates, and what happened. Then when I was an undergraduate, I had an interesting history class. It was all about why things happened. But I think historical seismology is sort of the gateway drug [laugh]—

ZIERLER: [laugh]

HOUGH: —into the history of science.

ZIERLER: Has USGS been supportive? I mean, in other words, do you take sabbaticals when you write a book? Is that sort of like a nighttime hobby? How do you integrate that with your full-time work?

HOUGH: Yeah, it's a hobby or avocation. USGS ethics rules allow scientists to write on their own time, and it's really not a matter of profit per se. [laugh] You don't get rich writing nonfiction science books. A big part of it, I think, is being a storyteller at heart. One of the reasons to write a book like Richter's Scale apart from my USGS position is that when you write for the USGS, there are endless levels of review, and every statement has to be very precisely stated and qualified and referenced. It's really hard to write for a general audience – to tell stories - and meet all those requirements. Writing books as what's called unofficial expression was really the only way to write like I wanted to write. The ethics rules within for the government are actually fairly clear and quite sensible. They don't allow you to go and profit from the work that you're doing as part of your official duties. I couldn't go consult on seismic ground motions and be paid for it. But they allow you to draw on your general knowledge of the field for outside writing and speaking, as long as you're not taking your official work and somehow parlaying that into a for-profit activity.

ZIERLER: Sue, was there an original idea or an individual that inspired you to jump into nonfiction writing like you have?

HOUGH: I think growing up, I sort of tore through some of the work by the top science writers, starting with Stephen Jay Gould. Through high school I was reading everything I could get my hands on by him. Let's see, who else? There were other writers, but I always enjoyed reading that kind of story. There's sort of a storytelling aspect of it that I enjoy reading, and writing. I enjoy kind of looking at the more personal sides of stories. Let's see. I had another thought but I lost it.

ZIERLER: Between either how small the field was at its origins, or by just the mode of science, how the science gets done, do you see seismology as being particularly conducive to storytelling? Is there a natural narrative that's there to grab onto?

HOUGH: Well, it's the one science that I know. But, yes, I think the way the field developed, it's conducive to that. Physics was an active field of science for a long time, and seismology really got started as a modern field of science in the late 19th century. There's a lot of relatively recent interesting history that you can piece together. I guess I haven't thought about what another field would be like. But there were good archival collections for the work that I've done: Robert T. Hill, who was active from the late 19th century through the mid-20th century, Bailey Willis, and then Charles Richter. A lot of the interesting stories, and the interesting characters date from the mid-19th century through the present. Seismology is also conducive to storytelling because there's often an interesting intersection between science and societal interests.

ZIERLER: Sue, what I'd like to do is if we can take all of your knowledge, everything that you've gained from researching all the books and articles you've done, and sort of put them into an amalgam of answers, really tracing the origins of the Seismo program, the Seismo Lab at Caltech. Going back to the 1920s, is your sense that the origins of the Seismo Lab really were about needing a central point of excellence in science? Was that really the tipping point that allowed the Seismo Lab to become what it eventually would be?

HOUGH: Yeah, I think Harry Wood was the one real driving force, going back to 1915, 1916. There was already a nascent seismology community in the Bay Area, work done after 1906, and Wood was at the forefront in realizing that there must be an earthquake hazard in Southern California. He wasn't the only one, but he was the one who was spearheading proposals—the Carnegie Institute was the main one that I know about—proposing to develop a seismological research program but anchored by a local seismic network. Still today, monitoring networks tend to really anchor earthquake programs. That got started, and it took obviously some time and some development. But the proposals were initially funded around 1920 or 1921.

ZIERLER: Was the Seismo Lab involved from the beginning not only in utilizing the detectors but improving the technology of detection?

HOUGH: Yeah. Seismology, as of 1920, seismometers were these behemoth, big, heavy instruments that mostly recorded what we call teleseismic waves, so waves you'd never feel from large earthquakes around the world. A magnitude 8 happens in Japan, and the waves are a very, very slow, long period, and these seismometers would detect them. But they weren't good at recording local earthquakes. The Seismo Lab was founded initially to look at local earthquakes, and they realized that there really wasn't an instrument that fit that bill. Wood teamed up with John August Anderson to develop a different type of seismometer. It should have been called the Anderson-Wood Seismometer, but most people call it Wood-Anderson. I think models still exist at the Seismo Lab somewhere. It's this nifty little device, very different design than had been used in the past, designed specifically to record local earthquakes.

That was a really key step. There weren't off-the-shelf seismometers that they could've installed at the time. Then there was still a gap that those instruments—Wood-Andersons—get blown off scale if there's a big earthquake nearby. They were designed to be very sensitive, able to record waves from small local quakes. By the '30s, there was another phase in instrument development that wasn't done at Caltech, to come up with strong motion instruments that would actually record big earthquakes on scale. This gets back to what we talked about earlier: instrumental seismology diverged early on based on the instrumentation. You had these sensitive instruments to record local earthquakes that would get blown off scale if anything big happened. Then you had instruments that would only record big earthquakes. So there were two parallel tracks in seismology for a long time. As the instrumentation's gotten better, the tracks come together.

ZIERLER: I'm curious, in your research, if you ever came across any interesting information about either the scientific or the administrative reasoning to have the Seismo Lab sequestered off into the hills in a mansion away from campus?

HOUGH: You want quiet sites to develop instruments. The original Seismo Lab—which it was actually the Kresge Lab—I was able to visit it after it had been sold but before Caltech lost the access to the property. It was a hoot. I don't know if that structure is—what's happened to it. But it was built in the San Rafael Hills, and there were caves built into the hillside. In Southern California, most of the LA/Pasadena area, people live within big sedimentary valleys where sediments have washed down over millions of years. They aren't great sites for sensitive instruments because the sediments have a big effect on shaking. You really want quiet recording sites -- for most purposes, you'd like to have seismometers on bedrock, not sitting on a bunch of sediments. The Seismo Lab team first had office space at Mount Wilson, I think because that's where office space was available. But then the Kresge Lab was built into the San Rafael Hills in a very quiet part of Pasadena, with vaults that were built into the hillside to where you could get instruments onto more competent rock.

ZIERLER: In moving the lab in the 1970s to campus then, obviously, what was lost?

HOUGH: Well, they kept the Kresge Lab, so they moved the offices. Instruments stayed at the Kresge Lab for some years afterwards and then, eventually, it was sold, and all of the instrumentation was moved. The original Pasadena Seismic Station, PAS, had been in place since the 1920s. It got moved somewhere in the vicinity but they lost—that had been [laugh] a recording site going back to like 1927.

ZIERLER: Sue, during the early years, was the Seismo Lab representative of a particular side of a debate that was happening more broadly in seismology at that point?

HOUGH: [laugh] There've been lots of debates. At the beginning, there was a debate about the severity of seismic hazard in Southern California, and that was The Great Quake Debate that I wrote about. It's sort of interesting. [laugh] Officially, you had business interests that were trying to down play the severity of seismic hazard. There were some statements made that seemed very laughable on their face, that Los Angeles was as free from risk from acts of God as any city in the US, and that type of thing. I think that the early scientists—Harry Wood and Charles Richter—before long were treading carefully, and not making alarmist statements. If you look at what business interests and city boosters were saying, it was clear that they were very worried about scaring away capital investors from the East with talk about earthquake hazard. If you look carefully at what they were doing, they were [laugh] aware of earthquake hazard, and they were taking fairly prudent steps to understand it. Business leaders and city boosters were talking regularly to Harry Wood, for example. There were a number of influential early committees established to look at earthquake hazard. Some were scientific committees, but there were committees on the business side as well. There was a lot of cross-pollination in membership, and in other ways. Business leaders invited Harry Wood to come talk to them, and that sort of thing. So there was a debate, but I'm sort of going to give away the punchline of my book. [laugh]

ZIERLER: What were some of the bases for the debate? In other words, were people talking about earthquakes as being predictable phenomena that occurred cyclically?

HOUGH: There was a prediction that brought issues to a head. Bailey Willis, who was at Stanford at that time, came out with essentially a prediction that Southern California was going to be rocked by an earthquake comparable to 1906 within five years of 1925. The prediction was, in short, bogus. It was based on flawed data. We still don't have the scientific framework to make that kind of statement that an earthquake's overdue within five years. When that prediction came out, there was a move to fight back, and specifically to counter that prediction.

ZIERLER: This was led by Robert Hill?

HOUGH: He was the main scientist who spoke out publicly. This was still back when scientists were working very hard to establish the monitoring network in Southern California. It's always a fine line in seismology that if you want to raise money for earthquake science and earthquake monitoring—

ZIERLER: You have to scare people but not too much? [laugh]

HOUGH: Yeah, you have to stay on the right side of the law. People tend to sort of not worry about earthquakes because they don't experience them very often, so you have to hit them over the head that earthquakes can be serious. Just because we haven't seen a damaging one in 50 years, that doesn't mean there's no risk. You're dancing with that fine line, then always, still today. Bailey Willis was dancing a lot closer to it than other people, but for the most part was suiting the community's purposes, to raise concern for earthquake hazard. He was out there making noise, and he went a little too far over the line. Once a scientist oversteps like that, it becomes an easy target to debunk.

ZIERLER: Sue, if Robert Hill's contention has aged better, in other words, it is pretty much the consensus view now that earthquakes, so far as we can tell, are fundamentally unpredictable, what was his insight? Was he looking at data, and was he coming to essentially the same conclusion that modern or contemporary seismologists would be coming to today?

HOUGH: Some of his insights have aged well. If you look at the arguments that were made about earthquake predictability, people including Bailey Willis pointed to the fact that, oh, there were earthquakes in Southern California in 1769 and 1812 and 1856 and, oh, look, that's a 50-year pattern. Even then, looking critically at those arguments, it was clear that they weren't sound because you're not talking about [laugh] a repeat of the same earthquake. I think in that argument and in a few others, Hill was more insightful, and maybe just more honest, refusing to over-interpret the data. He and other earth scientists knew that there was hazard in Southern California. The San Andreas Fault had been mapped after 1906, most of it, all the way down to at least San Bernardino, and they knew about the San Jacinto Fault. So scientists knew there was earthquake hazard in Southern California. It was just a matter of being honest about the limitations of what you could say about future earthquakes. There were other statements he made that didn't age very well: that there was no great menace from the Newport-Inglewood Fault. [laugh] That didn't age well. Some of those statements that didn't age well, I concluded he was off base because the field as a whole didn't understand some fundamental scientific issues.

It's interesting to look back. What did people think, and why did they think it? You realize that, sometimes, the frameworks were just so far off base that you could make a very reasoned, sensible argument, but your premise was wrong. One of them that Hill made was based on the almost universal—well, not quite universal. But, at the time, people believed that earthquakes accommodated vertical motion, that faults move things up and down but not sideways, and not to great distances. That was contentious for a long time. Hill concluded that seismic activity in Southern California was declining. And you wonder, where did he come up with that? It turns out that the vertical…the mountain building in California was way more active, going back 30 million years, because the plate tectonics was different. Now, you have a lateral San Andreas Fault through most of California. You used to have subduction, forces pushing up the Sierra Nevada and the Transverse Ranges. So Hill was quite astute to realize back in the early 20th century that mountain building in California is less active than it was in the geologic past. But he didn't appreciate [laugh] that there was a whole lot of lateral faulting going on because nobody understood plate tectonics really until 1960 or so. [laugh]

ZIERLER: A question you've thought about a lot, I'm sure, why is Richter a household name, and Gutenberg is not? How did that happen?

HOUGH: [laugh] It was the Richter Scale. Richter started at the Seismo Lab in 1927—I want to say somewhere in there. For decades, he was the one scientist who was most willing to talk with the media, so people started to see his name like in the local papers. But there's a letter from a seismologist at Berkeley, Perry Byerly, who was there for decades, a contemporary of Richter. He was talking about the magnitude scale, and a reporter asked him what they should call it. Byerly apparently answered, "Call it the Richter scale." That's really where the iconic name recognition comes from because that caught on. The paper, the Richter scale, it was published in 1935, and there's some debate about, controversy about this too in some quarters. It was a single-authored paper published in 1935 that developed, presented this first ever scale to rank the relative severity of earthquakes, and it was tuned for Southern California.

In this paper, Richter acknowledges, I think, Gutenberg for suggesting making the scale logarithmic, because you have a huge range of earthquake magnitudes, and if you want to collapse a big range of numbers, the logarithm is handy. I think he acknowledges Wood as well. Then one part of the scale he developed draws on earlier work from a Japanese scientist. My reading of that paper was it really was his baby. It was a project that he was substantively leading, and that the insight and the inspiration and the perspiration was his but with some input from colleagues along the way. Once the scale was introduced, the idea quickly took off , and Gutenberg was quickly involved with subsequent developments of the scale—and other people as well. If you do something that's really notable and useful in science, it'll take on a life of its own. It's sort of a hallmark of a really seminal contribution. Eventually there was a buzz that, well, it should've been the Richter and Gutenberg or Gutenberg and Richter scale—and I don't think so. I think that it's appropriate that Richter's name be on it. There's a further point that if you talk to seismologists today, they will tell you that we don't use the Richter scale anymore. We should call it some other magnitude scale. It's true. It's a subtle point but the way we measure magnitudes is different, and the scale was—people realized that the formulas he came up with didn't really work well for big earthquakes. The way we measure magnitude is different. But if you think about magnitudes, we report magnitude 3, magnitude 6, magnitude 8. There's no units on those numbers. It's not joules or mega-joules or anything. It's a relative scale that Richter came up with. He defined what a 3 is. He defined what a 6 is. He defined what an 8 is. He referenced 1906 as probably close to 8. Those definitions are still in use. We are using his scale, so I think should be reporting magnitudes as equivalent Richter magnitudes. I think seismologists have confused people over the years by saying, "Well, it's not the Richter scale."

The Meaning of the Richter Scale

ZIERLER: That's to say on the evening news, if they report a 7.2, that's the same 7.2 that Richter would've called it?

HOUGH: Conceptually, it is. What does a 7.2 mean? It's still dovetailing back to his definitions. If you read the paper, 6 is a moderately, locally damaging earthquake, for example, and that's the way he tuned the scale. A 3 is a maybe a shock that's felt locally. He defined the scale so that 0, the smallest earthquake he calculated, could be recorded at the surface under ordinary conditions. That's held up. If you have a seismometer at the surface, smaller earthquakes have negative magnitudes because the scale is logarithmic. But you almost never see those, even today. There was an awful lot of insight into the way the scale was set up and tuned to produce numbers that are kind of—what's the right word? They're not meaningful in terms of units but are kind of relatable. I would say what we would estimate as a 7.2 is an earthquake that Richter would've regarded as that same magnitude.

ZIERLER: Another name that's been not nearly as remembered in history as Richter, of course, is Hugo Benioff. Do you have a sense of why, as an instrument builder with the seismographs, why have we forgotten his contributions, at least at the popular level?

HOUGH: Very few scientists are ever famous. In recent decades people have known a few seismologists, including Lucy Jones and Kate Hutton, because their names were in the paper. But a person is not going to be remembered as a scientist because they were the go-to expert of the day in a certain era. There are plenty of scientists, including Bailey Willis, who might have been known in their day. Willis was a go-to guy for newspapers in the early 20th century; Hill was another. Today almost nobody has any clue who they are – of the two Hill is the better known, for seminal work sorting out the geology of Texas. Benioff is certainly well known among Earth scientists. Within seismology, we talk about Benioff zones, that is earthquake zones associated with subduction. There's a ton of recognition of his contributions in seismology. But he didn't ever do anything that ended up with his name attached that the public saw. Hopefully someone will write his biography someday – I think he was another interesting character. But the bottom line is, no matter how accomplished they are, scientists are rarely ever famous. I tried to think of another Earth scientist that's known to the public, beyond Richter.

ZIERLER: Maybe Richter, that's an unfair comparison. It's really because of the Richter scale that we have that name association.

HOUGH: People point out that the public can't generally name very many female scientists. But then ask a member of the public to name 10 male scientists, and [laugh] I think a lot of people would struggle. It's like, well, there's Isaac Newton, and there's the guy who was in the wheelchair. Are there any geologists, say, that most people would recognize? Male or female?

ZIERLER: Sue, in thinking about the history of the Seismo Lab, how well do the directors over the years serve as a stand-in for eras within the lab? In other words, is there a significant transition that you see from Wood to Gutenberg, or from Gutenberg to Press that really defined narrative distinctions in terms of what the lab was doing?

HOUGH: I'm not sure. I haven't seen the whole arc. Wood led the charge to start the Seismo Lab to monitor local earthquakes. When Gutenberg came in with a much more global view—he was from Europe; a leading expert in global seismology—and when he came in, and that would've been 1930-ish, that brought a shift towards more global seismology. Wood ended up lamenting the lack of attention to local earthquakes. There was that early shift. Then from 1930 through I think 1990, I'm not sure. I think the Seismo Lab's relationship with the seismic network has evolved over time. There have been periods of questioning whether or not Caltech should be running a seismic network. Isn't that something that should be left to a governmental organization? It's not really research. I'm not sure where that pendulum was at different times. But I think from the time that I got there, there was increasing recognition that the network is really a world-class research resource, and it really drives so many aspects of earthquake science. It's one of the preeminent regional seismic networks in the world, from the beginning and still today. At this point Japan has the most sophisticated networks; they've become the gold standard. But the California network – recently the California Integrated Seismic Network – remains world class as well. And an awful lot of the science is driven by data collection.

ZIERLER: I'll share a sense I'm getting from how the Seismo Lab sees itself, and you can interrogate the nature of the assumption. But, in the early years, at least for the first 20 or 30 years, the Seismo Lab saw itself in many ways as the center of the world in seismology. Obviously, that changed over time. First of all, is that fair? Were there competing institutions that might have also laid claim to that title? What were the factors that knocked the Seismo Lab I don't want to say off its pedestal but made it less singular in the field perhaps?

HOUGH: I think Caltech has never suffered from a lack of [laugh] confidence.

ZIERLER: [laugh]

HOUGH: There were early observatories elsewhere in the world. The Jesuits were running observatories around the world, going back to around 1900. From the very early days of instrumental seismology, there were Jesuit institutions in the central US. Caltech was never—they were not the earliest institution to be running a seismic network. When the network went in, in the 1920s, as far as I know, it was the earliest local regional seismic network, the first use of Wood-Anderson instruments to monitor local earthquakes. [unrelated conversation] The earthquake catalog for Southern California, that I know, is the oldest continuously produced earthquake catalog in the world. Seismologists who focus on earthquake statistics do a lot of work with the catalog because it's been continuously produced since '32.

ZIERLER: Sue, what about the concept of data sharing? In other words, in the early years of the Seismo Lab, the data that the lab had was almost proprietary. It was theirs, and people had to come to access it.

HOUGH: Well, in the early days the data were recorded on paper and film chips, so it wasn't that they wouldn't share it as much as you couldn't share it easily. It wasn't digital. So far as I know, if other people were interested in looking at the data, it would be made available but, physically, you had to come to where the data was. That was just the way it went. Seismic networks produced bulletins from early on. In a recording of an earthquake, there's an initial P-wave, followed by a later S wave, and other types of waves. Early analysts determined the arrival times of P waves and S waves, observations that were used to local earthquakes. Those bulletins would be shared, typically sent by mail or otherwise published. Once data started to be digital, it was a new era – data could be shared easily. The transition to digital data, that happened at a time when the USGS was involved in seismic monitoring. [unrelated conversation] As a public agency, the USGS has a foundational mandate to share any data the agency collects. As network operations became increasingly digital, then the data sharing happened very organically. But I don't think there was a philosophical unwillingness to share data, even in the early days.

ZIERLER: The democratizing effect of having data that's shareable, what did that do to the Seismo Lab's stature in the field? In other words, at some point, because data can be shared freely, did it cease to be or did it become less so a magnet, a place to be to do research, to attend talks, to interact with the cutting-edge research?

HOUGH: It might've gone that way. But I think the Caltech Seismo Lab has remained a preeminent seismology group, going back to the beginning. There is a lot of research done on the data in other places. So a school like UCSD, Scripps Institution of Oceanography is now doing cutting-edge research with data from the seismic network. But nobody's ever knocked Caltech off the pedestal. I think part of it is being where the data are collected. Part of it was an evolution of departments. I was in grad school in the '80s, and there were a number of groups at that time doing seismology. A number of those got smaller over the decades that followed. Caltech sort of held its own. If you look back at the history of Earth science, a lot was going on in the latter half of the 20th century. You had the plate tectonics revolution starting in the 1960s – a new paradigm with exciting new ideas. There was a point in 1970 when seismology was a hot science. You had a big expansion of global seismic networks in support of treaty verification; you had the launch of the National Earthquake Hazard Reduction Program. The USGS got involved with seismic monitoring, so there as a big increase in data quality and quantity. For a time there was optimism that reliable earthquake prediction was within reach. All of this fueled a sort of golden era. Then, over time, Earth science wasn't the hot thing anymore, and other sciences, including the biological sciences, came more to the fore. Even within Earth sciences, other disciplines besides seismology have gotten to be more important. Climate change, for example. But through the latter half of the 20th century there was a lot of excitement and energy fueling the field of seismology. Then for various reasons that waned; smaller earth science departments broadened their portfolios, with less focus on seismology, while the Caltech Seismo Lab remained more focused. Maybe this would be a good time to note that we say "Caltech Seismo Lab" now, but at the beginning it was only "Pasadena Seismo Lab," supported by the Carnegie Institute.

The Plate Tectonic Paradigm Shift

ZIERLER: Sue, I'm not sure if you've had this idea that, in the '60s and into the early 1970s, all of the revolutions in plate tectonics sort of passed by the Seismo Lab; that the Seismo Lab was not central to these developments. I wonder if you've heard the same thing, and what the basis is to this?

HOUGH: It may have been my first book. [laugh]

ZIERLER: [laugh] OK.

HOUGH: Or rather, the idea didn't come from my book, but it was something I heard at the time. In my first book, Earthshaking Science, there's a chapter on the plate tectonics revolution. It built steam slowly and then, all of sudden, there came a point where that was just the hot, new ideas, and there was a lot of excitement. Paul Richards, who is a preeminent theoretical seismologist, now retired, reviewed the book. He was a postdoc at Caltech when some of the exciting initial developments played out, and he said people there just weren't that excited about it. They had other things they were focusing on. I think there's a recognition, looking back, that when you look at all the seminal contributions in that revolution, Caltech Seismo Lab wasn't a big player in that particular chapter.

ZIERLER: Was there historical or intellectual baggage, since Seismo Lab has this deep history, that might help explain why it wasn't a major player?

HOUGH: I'm not sure. They did for a while have a focus on global seismology, so understanding deeper structure, sort of the Earth as a planet. But I don't know. It'd be interesting to talk to somebody—and there are a few people around, for example Paul Richards—why they thought there wasn't more interest. It may come down to just a small number of individuals, and what they're interested in or not interested in. During my time in Pasadena, for example, I started working on induced earthquakes. I ended up doing a project with Victor Tsai, who was on the faculty at the time. Victor is an all-round fabulous scientist who's interested in everything. He was aware of my work, and had some ideas, and so we started talking together, and that turned into a collaboration. Then the Seismo Lab was involved with induced earthquake research. But then Victor left for Brown University; our collaboration wrapped up, and our research interests diverged. Is anyone at the Seismo Lab now interested in induced earthquakes? I'm not sure. But the point is, what a department is or is not interested in often boils down to what a small number of scientists are interested in.

ZIERLER: Sue, I'm curious, particularly in light of your graduate work at the Scripps Institution of Oceanography, if you have a sense if there was ever a conscious decision made at Seismo Lab where it would not be a center of ocean-based geophysics research. Was that in light of the fact that Scripps was there, that it would fulfil that role?

HOUGH: I don't know. The oceanographic institutions do tend to be on oceans. [laugh] You have Scripps. You have Woods Hole. I don't know why the Seismo Lab never moved in that direction, apart from the obvious fact that Pasadena is not next to the ocean.

ZIERLER: The timing in the 1970s, as you called it, this was the heyday for earthquake prediction. What was going on at that point that gave optimism, that this was something that was feasible?

HOUGH: It was like more in the '70s.

ZIERLER: Yeah.

HOUGH: When I started writing my prediction book, I had a cynical view that various people in institutions were pushing to launch NEHRP, the National Earthquake Hazard Reduction Program. Frank Press was a big player in that. It was a kind of strategic interest: leading seismologists were arguably using earthquake prediction as a carrot, pointing at apparently successful work that was being done in China and the Soviet Union, to argue for a new federal program. There was a swirling of Cold War [laugh] issues at play: we needed the federal program because the Chinese and the Ruskies were ahead of us, and we needed to catch up. When I started to write my book, I cynically thought that it was really a matter of politics, the bubbly talk about earthquake prediction. But then I talked to a number of people, scientists who were maybe 10 years older than I am, who were actually around through the '70s. They talk about a genuine interest or genuine excitement that prediction was within reach, and meaningful short-term prediction.

There were a couple of developments right around 1970. One was the theory of what's called dilatancy. It's a theory that came out of laboratory work that if rocks are being stressed, their physical properties will change. If you think about it conceptually, if you have stresses building up generate to a big earthquake, the physical properties may change in a way you can detect, and know that an earthquake is coming. This idea was the basis for concern about the Palmdale Bulge – an apparent observation that a patch of the Mojave Desert north of Los Angeles had bulged upwards in recent decades. Then there were induced earthquakes, which were first recognized in the 1960s. Scientists realized at that time that when fluids were pumped into the crust, it sometimes made earthquakes happen. People started to have the sense that, OK, we're understanding how earthquakes work. We understand plate tectonics. We understand what triggers earthquakes. We understand how rocks may react to build up of stress. I talked to some very smart scientists who were around at the time – they tell me there was genuine excitement that prediction was within reach.

ZIERLER: I'm curious, as we get into the 1980s, what is the overall sense of the Seismo Lab's contribution to accepting that earthquakes are fundamentally not predictable?

HOUGH: Well, I think they were ahead of their time in some respects. Frank Press, one of the big movers and shakers of his day (so to speak), jumped on the promise of prediction. But Hiroo Kanamori has been a driving force at the Seismo Lab, going back to the '70s. He's been there a long time, one of the preeminent seismologists of the second half of the 20th century. I don't know if you've had a chance to talk with him…

ZIERLER: Yeah.

HOUGH: He's an amazing guy. [laugh]

ZIERLER: He comes into the office every day.

HOUGH: We haven't touched on a whole other chapter of the Seismo Lab, involving their track record with diversity, equity [laugh] and inclusion….

ZIERLER: We'll get to that. That's on the list.

HOUGH: OK. We may run out of time. But there've been issues at the Seismo Lab. They were legendary, kind of old-school, old-boy. It's been a problem. When I was an undergrad, I was at Berkeley, I asked Bruce Bolt for his thoughts on grad school. In retrospect, he and a couple other professors I talked to never mentioned Caltech. It may have been partly Berkeley-Caltech rivalry, but I think it's because they knew that the Seismo Lab wasn't a good place for a female students at that point. But Hiroo, he cares about science. What do the data show? I'm convinced that you could be green and, if you came to Hiroo with interesting ideas about science, I don't think he'd notice that you were green. He's just a really amazing scientist who does not care about politics. Getting back to prediction, Hiroo wasn't vocal about it, but he was a skeptic of prediction, even during the heyday. Richter was more vocal. He was the skeptic speaking out because he thought the prediction claims were being oversold.

ZIERLER: Sue, it is an important topic. I do want to get to it. To clarify, if you were given advice not to go to Caltech, or it was specifically omitted, and you're reading into why, that's an important point because there's obviously the historical reality that 30, 40, 50 years ago, very few places or no places would've been good for women. But you're saying even within that context, Caltech, the Seismo Lab, was specifically not good relative to other peer institutions?

HOUGH: Yeah. They never had a good reputation. Lamont the other one, Lamont-Doherty, now, Earth Observatory.

ZIERLER: At Columbia?

HOUGH: At Columbia, yeah. The two of them, I would say, [laugh] are kind of in a league of their own. When I was at Lamont, they had their 40th anniversary as a research institute. Lamont has always had some scientists who are or were on the faculty at Columbia, and then they have soft-money scientist whose salaries are paid by external grants. When I was there at their 40th anniversary, they had never had a female faculty member at Lamont, ever. There and at the Seismo Lab, it was just the culture of the place. Academic departments always have their own cultures. The tone is set by people at the top. [unrelated conversation] It may depend on one or a small number of people. Scripps, the group I was with was better than most, and there were a few people there that were setting the tone in a good way -- Bob Parker and George Backus, to name a couple of names. This was IGPP, the geophysics group at Scripps. There was another group within Scripps that had a horrible reputation back then. It's very dependent on a few people, what tone gets set and what tone gets perpetuated. It was really my generation in the '80s when women started to show up in grad show in appreciable numbers. Before then, there were women but they were fewer and farther between. When they started to show up, it was just a better environment in some groups than in others.

ZIERLER: As I'm sure you know, in higher education across the board, and at Caltech specifically, efforts to improve equity and diversity and inclusivity are really at the top of the agenda. Have you kept up with the Seismo Lab, and do you have strong opinions on whether it's improved in accordance with the times?

HOUGH: I think they are making up for it [laugh], considering that they got a late start. It's hard to say. You are dealing with small-number statistics. Victor Tsai was hired maybe 10 years ago – he's Asian-American, and Asians aren't necessarily underrepresented in science but they can be in Earth sciences. But then he left. Pablo Ampuero was another recent hire – he's from Peru. He also ended up leaving, and not because he was denied tenure. For various reasons, Pablo and Victor were hired but ended up leaving. But things are getting better. For a long time, the Seismo Lab liked to double-count women. [laugh] That is, the few women who were hired had joint appointments: geology/Seismo Lab or engineering/Seismo Lab. It was essentially half of FTE, which I thought was better than nothing. I would need to look at a roster of faculty to know what the balance is at this point, but diversity is improving.

ZIERLER: Sue, in the way that we've been talking about the Seismo Lab in sort of historical narrative chapters, over the past 20 years, what are some of the highlights in that chapter? What has the Seismo Lab been known for in its modern era?

HOUGH: That's a good question. I might need to think about that one more. The focus on network seismology, with operation of a world-class network, has fueled advances in both methods to predict how the ground will shake in an earthquake, and what we call seismotectonics. Seismotectonics is basically the interface between earthquakes and geologic/tectonic processes. Global seismology has been a big continuing focus: understanding great earthquakes, and the earthquakes themselves, and also understanding Earth's structure. That's been an important continuing focus.

Communicating Seismology

ZIERLER: Sue, for the last part of our talk, I'd like to touch on your career really in science communication in communicating seismology to the public with a focus on what the Seismo Lab's research has contributed to what you've been able to explain to the public. Perhaps at the most general level, what does the public want to believe as true when it comes to earthquakes? Then we'll get to the hard medicine of what you have to tell them. What does the public want to hear?

HOUGH: They usually want to hear that they don't have to worry. If you just had a big earthquake, "Oh, you're just going to have aftershocks but the aftershocks are going to die down." But we can't ever say there won't be an earthquake. People want the assurance, and often we fundamentally can't reassure them, at least not beyond a certain point. It's sort of ironic. Modern statistical seismology tells us that the odds of a large earthquake are never higher than right after a big earthquake has just occurred. The time to be most worried is actually right after you've just had a big earthquake. That's because earthquakes always have aftershocks, and that's the one time you can sort of make meaningful predictions about the numbers and rates of expected earthquakes. But the numbers are so high that there's a chance you're going to have a quite large aftershock. There are some measures of reassurance we can give people, for example involving the likelihood of big earthquakes, and likelihood of damaging shaking. But people don't like earthquakes, and there's not much you can tell them that would be fundamentally reassuring—not in California, anyway.

ZIERLER: That's on a macro timescale, of course. What about, Sue, on the micro timescale? What do people want to hear when it comes to having as much advanced warning as possible when the big one's about to start, and where does the Seismo Lab fit into those advances?

HOUGH: Early warning is possible, yes, and the Seismo Lab has had a big part of that really since the beginning, so going back 10, 20 years, coming up with methods to recognize that a big earthquake has happened, and then get the warning out in advance of the strong shaking. That would be a highlight of work done over the years, development of methods that are now used for early warning. We do now have the early-warning systems on the West Coast, and there's still quite a bit of work to be done, understanding their limitations and fine-tuning the messaging. I think the people would very much like a heads-up that strong shaking is going to happen. Obviously, we take away that element of surprise that makes earthquakes really terrifying -- that one second, you're minding your own business, and the next second, your world comes unglued, and that's fundamentally unsettling. That is something that seismology can potentially provide.

ZIERLER: Where are we now? How much realistically do we have in terms of time? How long can we prepare people before the shaking starts? Seconds, minutes? Where we are now?

HOUGH: Not minutes, and that's the problem. If a magnitude 7 earthquake happens 100 kilometers away or 200 kilometers away, you have time to detect the earthquake, get the warning out, people get tens of seconds. But if you're sitting in Northridge, and a Northridge earthquake happens, there's no time to get out a warning. There's always what they call a blind zone. For any earthquake, if you're sitting on top of it, there isn't going to be time for a warning. There's the also the problem that if you want to get warnings out fast, you don't want to sit around for 30 seconds, and figure out how big the earthquake is exactly. You need to err on the side of getting that warning out fast. So an earthquake happens, and it might be big, so you err on the side of getting a warning out. Most of the time, the shaking won't be severe. If you want to warn people for severe shaking, you pretty much have to warn them for weak shaking too. But then are you conditioning people to ignore the alerts because the alerts they get are mostly going to be for weak shaking? That's where the devil's kind of in the detail. [unrelated conversation] Figuring out how you want to set the alert levels, what the messaging should be, there's just a whole lot of work being done on that still.

ZIERLER: A topic that permeates all of your writing, the notion of unpredictability, my question might touch a little bit on the philosophy of science. How do we delineate between our limitations in understanding earthquake predictability versus the Earth itself not knowing when it's going to start shaking? If we want to assert the latter, how can we be sure that it's simply not a limitation of our own theoretical and instrumentation analyses?

HOUGH: I guess this is sort of a philosophical debate in science. There are these terms "epistemic uncertainty" and "aleatory." "Epistemic" is the not knowing. "Aleatory" is the Earth being complicated and unpredictable. There is a purist school of thought that if you understood everything well enough, you could predict everything; that everything on Earth is controlled by physical laws than in theory, so in theory we could understand everything. And if we can understand it, then we can predict future behavior. I don't ascribe to that school of thought – that is, there are physical laws, but there's also so much complexity that I don't think we'll ever understand complex processes in fine detail. I don't think we're ever going to be able to predict a lot of things in detail because when earthquakes happen all the time, the question is why does one small earthquake keep going and get bigger? In theory, if you knew every single thing about a fault in the Earth, and the state of stress, you could predict the future behavior of a system, but it just depends on innumerable little details that you'll never know. [laugh] It's an excellent question. There's sort of the philosophical debate of are things fundamental unknowable? Then, practically, can we make headway?

ZIERLER: It sounds like both can be true. We can make headway without ultimately getting to that goal, it sounds like.

HOUGH: Right, or could some aspects of a system fundamentally be predictable even if we can't predict what every little earthquake is going to do? There's still an awful lot that we don't know.

ZIERLER: Sue, I'd like to ask two last questions, both looking to the future. First, for the Seismo Lab, given your deep appreciation of its history, where do you see it headed? What are some of the big areas of science that it should focus on looking into the future? If there is more work to be done on the diversity side, what can it do to encourage more underrepresented people from joining the field generally and the Seismo Lab specifically?

HOUGH: One exciting new direction is being driven by the new monitoring technologies, and the new computational technologies. Seismology has become more and more data-intensive. You have more data, and new machine-learning approaches to analyze it. Zach Ross is one of the best young researchers I know who is working on machine-learning applications. Zhongwen has been doing some really innovative work with distributed acoustic sensors, DAS. Really, that's kind of in the best tradition of the Seismo Lab pushing the science forward by capitalizing on new approaches to collect and analyze data. I expect that we're just scratching the surface of what's going to come out of that kind of study because it's really revolutionizing seismology in terms of the amount of data that you have, and the methods to analyze it. I expect that's going to keep going for some time. In terms of diversity, it's tough in some respects. I've seen departments lose good people and diverse people because they won't come to grips with the two-body problem. You may have a scientist who you'd like to keep, female or underrepresented minority, or even while male, but they have a spouse with their own career. Universities are really bad in general at making attractive offers to a pair of scientists, even when they're both stellar. It's just, I think, one department doesn't want to feel like they have to hire somebody because another department wants to hire their or keep their partner. If universities as a whole could be better with that, I think it would help everybody. There is still a real issue, that there are so few underrepresented minorities in Earth sciences, even at the graduate school level. That's still a pipeline problem, attracting talented minorities. I think there is work being done, at Caltech and elsewhere, to address some of those issues.

ZIERLER: Finally, last question for you, Sue, either for the next book project or the next research work, what do you want to do that you haven't done yet?

HOUGH: [laugh] Sleep.

ZIERLER: [laugh]

HOUGH: I've got a list of projects at any given time that I'm trying to push forward, and I haven't run out of ideas yet. I don't have a new book idea. The Great Quake Debate, I wrapped up the archival research in 2019, and the book itself, it was almost all written by that summer. Then the pandemic hit. My heart goes out to anybody who was trying to do archival research over the last two years. I would've been dead in the water. I spent hours at the Caltech archives, at SMU, at the Huntington Library, and that just isn't happening at this point. Or maybe it's just starting to be possible again. But in part because of that, I just haven't really been thinking about possible next books. We'll see. The Great Quake Debate, I wasn't really—that sort of bubbled up. I wrote the—I'm going to have to remember—the prediction book, and then I sort of took a break. Then I started to work on the 1925 earthquake, went to the Huntington Library to look at Bailey Willis's papers, and started to get interested in who this guy was. We'll see where things go next. [laugh]

ZIERLER: We'll see. Sue, on that note, I'm so glad I was able to spend this time with you, and for you to participate in the Seismo Lab History Project. I'd like to thank you so much.

HOUGH: Thank you.

[END]