June 23, 2022
What are the underlying physics that trigger earthquakes? This is perhaps the most fundamental question in seismology, and it is the driving focus of Emily Brodsky's research agenda. Following her undergraduate focus in geophysics at Harvard, Brodsky came to Caltech's Seismology Laboratory, where she was among the first academic generations to take advantage of seismic data available over the internet. This technological development proved revolutionary in the rapid analysis and distribution of earthquake information.
During her time on the faculty at UC Santa Cruz, Brodsky has pursued a broad range of research topics including volcanic tremors, hydrogeology, the impact of earthquakes on groundwater, and geysers, among others. Unlike many in the field, Brodsky is not convinced that earthquakes are inherently unpredictable. Brodsky's honors include the Charles Richter Early Career Award from the Seismological Society of America, the James B. Macelwane Medal from the American Geophysical Union, and the Price Medal from the Royal Astronomical Society.
DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It is Thursday, June 23rd, 2022. I am very happy to be here with Professor Emily Brodsky. Emily, it's great to be with you. Thank you for joining me today.
EMILY BRODSKY: Thanks for inviting me.
ZIERLER: To start, would you please tell me your title and institutional affiliation?
BRODSKY: I am a Professor at the University of California, Santa Cruz.
ZIERLER: Tell me about the department at Santa Cruz. Is it in growth mode? Is it an exciting place to be right now?
BRODSKY: Yeah, I think we're doing okay! We have arguably one of the strongest earthquake groups around, and we're also a very strong geophysics program in general, Top Ten in various rankings, if you care about those things. Generationally, we're about to do some turnover. It's a good place.
ZIERLER: Just for a snapshot in time, what are you currently working on?
BRODSKY: How long do you have?
BRODSKY: In general, I work on earthquake problems. I'm interested in the mechanics of earthquakes, how they trigger each other, what makes them start, how they get big. I also tend to work on other things that I feel are like earthquakes, like glaciers and landslides and granular phenomena friction, in a sort of fundamental mechanics sense. When I'm feeling glib, I say basically I like things that fail catastrophically. I also do volcanic eruptions, too. I do those things from a variety of angles. Some of it is seismological, but I also think that you're never going to learn about microscopic physics seismologically, so I also have a lab. We do analog experiments. I do bore hole measurements where I've taken the temperature of faults and look at hydrological properties. We also do some structural geology where we go out and actually look at fault outcrops and look at the scars of the earthquakes and what that tells us about process.
ZIERLER: A ripped-from-the-headlines kind of question, the devastating earthquake in Afghanistan yesterday, are you involved in that already? Are you following what's happening?
BRODSKY: Oddly, no. It wasn't that large an earthquake. I have not taken a good look at the Afghanistan earthquake other than what you have also read in the headlines.
ZIERLER: Is that because it's below a certain magnitude threshold where it doesn't necessarily come on your radar?
BRODSKY: There's a certain amount of that. There's a certain amount of I have other things I'm doing at the moment.
ZIERLER: What aspects of your research are more on the theory side and what are more on the observational or experimental side?
BRODSKY: I am pretty firmly an observationalist, and the experiments are an outgrowth of the observational piece. I am about interpreting observations. I always say the candle burns on both ends, that you try to go after things from first principles, and you go after things empirically, and you hope they meet in the middle. I do a certain amount of just flat-out statistics of earthquakes. One of the things I'm doing right this second is my student, Kelian, has just constructed a machine learning framework to forecast seismicity based on past seismicity. This outperformed our previous way to do it, which was based on these statistical models that were highly parameterized. This is a much more flexible framework and it does better when we use bigger catalogs. The parameterized version sort of saturated, it did as well as it could do, and then it stopped improving when you got to about 10,000 earthquakes, where currently earthquake catalogs are a lot bigger than that, and we could do better than that. That's a really very empirical approach to the problem. Can we predict what's going to happen next empirically with what we've done before? That's being an observationalist.
Then, another line of things that I do—I have another student, Huiyun, who is working on taking known perturbations of stress, cases where we know something got triggered either by human activity, like you pumped water in and out of the ground, or you had a large earthquake that shook the ground and those dynamic waves triggered it—all of those things can trigger earthquakes, and so you know the stress in, and you know the earthquake rate out, and so you can make some relationship between causative stress and earthquake rate, and you can do that empirically, but now you're getting a little bit closer to physics. I would call myself an observationalist, but it has a pretty strong theoretical implication. We're working out empirically those distributions, and what we have found in previous studies is that at least from the dynamic triggering piece, it appears that faults out there are distributed over the earthquake cycles in Southern California in a uniform way, so that you have as many earthquakes at a pascal from failure—as many faults at a pascal from failure as 100 pascals from failure. Now, we're beginning to ramp up or trying theoretically to reproduce that observation. So, it's a bit of a yes and yes.
ZIERLER: When you go out and do field work, of course it's a big planet, and resources are limited. What's most compelling to you when you make those decisions about where to go and what to study?
BRODSKY: Whether or not I'm really going to learn something, and that it's not just because it's there, but it's an opportunity to answer something fundamental. I helped orchestrate a fairly large project to drill into the fault after the Tōhoku earthquake. Here's my Chikyu mug. I have got a collection of coffee mugs here! There's my Expedition 343 mug. My students will tell you there's always a coffee mug somewhere near me.
ZIERLER: [holds up his coffee mug] Cheers!
BRODSKY: Yeah, there you go! That was because one of the big fundamental first principle problems in earthquake physics is what's the friction on the fault during an earthquake. The only way you could really figure it out was to go take a fault's temperature and measure the frictionally dissipated energy after an earthquake. To do that, you need a big drill ship to go run after a big earthquake, and we did that. There was a very clear decision there about what should be done, in part because we thought about it before the earthquake and we had identified a good question.
Currently I'm working on orchestrating a fairly large initiative called SZ4D to instrument a plate boundary in a way to understand the full earthquake cycle, in geological context, on a subduction zone. Again, in order to decide where and what to do, what we've been doing is we took a very systematic approach. We looked at all the segments of subduction zones around the world and systematically said, "Is there enough logistical and geographic context and is there enough scientific context, and does it move fast enough, and does it have the right kind of earthquakes?" All of those sorts of questions. "Is it generalizable?" When you get all the way down to that, we're heading to Chile. That's a long way of saying I pick where I go because I want to answer something, and I don't really care where it is. I've worked in the Basin and Range. I've worked in Italy. I've worked in China. I've worked in Taiwan. Japan, obviously. Kamchatka. A number of places. California, obviously. You go where there's enough context—that's part of it—and you can really answer a question.
Earthquake Prediction Prospects
ZIERLER: Given the centrality in your research agenda to really trying to understand the underlying processes that trigger earthquakes, where does that put you within the broader debates of whether or not earthquakes are predictable?
BRODSKY: It puts me in a very special place [laughs] which is that I am a very strong advocate of studying whether or not earthquakes are predictable. I don't think we know the answer to that question. I think there are enough hints out there, particularly in the current instrumentation era. There are hints that didn't exist before now, that are there now that suggest that they might be, under certain circumstances or—certain kinds of earthquakes might be predictable. I do think it is really important to study those hints. I think that claiming at the outset that they are unpredictable is as unfounded right now as claiming that they are predictable.
ZIERLER: As we both well know, there are lots and lots of seismologists who have thrown up their hands and declared earthquakes to be fundamentally unpredictable. In those debates, at conferences, in papers, what do you find the most effective arguments to say, "I'm not ready to go there yet"? How do you convey that?
BRODSKY: I have a slide for that, which is I lean very heavily on the 2014 Iquique earthquake as well as the 2011 Tōhoku earthquake, both of which had very strong migratory foreshock sequences and geodetic signals that are somewhat ambiguous but imply that there was a seismic—a slip event beforehand. There's some pretty clear evidence there that there's something worth studying for those particular earthquakes. Now, whether that applies to any other earthquakes, who knows, but it's also quite clear that we didn't have the right kind of data before now to ever even ask that question. It's a physically founded thought that is observationally founded as well. I think post-Iquique, I don't think people have been arguing about it as much as they used to.
ZIERLER: Do you see this in some regards in generational terms? In other words, are people who don't believe that earthquakes are predictable are of an older generation primarily?
ZIERLER: What do you think that's about?
BRODSKY: I think that's about PTSD [laughs]. They thought and were very optimistic in the 1970s and early 1980s about earthquake prediction, and it didn't happen, and they ended up in a very difficult place in terms of policy and having overpromised. They didn't see that they had succeeded in their lifetimes and thought we should move on as a field.
ZIERLER: What are some of the predictive technologies that might give you cause for optimism that ultimately this is where we can head?
BRODSKY: It's about the geodetic revolution and also the density of instrumentations. What we can see observationally now is unbelievable compared to what they could see. They were trying to do it on one lousy geodetic record here and there. I don't know how technical I'm allowed to be for this.
ZIERLER: I'm going to track you, but it's whatever you feel comfortable explaining.
BRODSKY: Geodesy is the slow defamation of the Earth, as opposed to seismology which is the fast deformation of the Earth. When I'm feeling snarky, the difference is whether or not you include ma. F = ma is seismology, and no ma is geodesy. In order to track the full earthquake cycle, I think people understood theoretically for a long time that you wanted to capture both the slow and the fast motion. There was a generation of efforts to capture that slow Earth motion as part of the earlier efforts at earthquake prediction, and the technology wasn't there yet. The EarthScope that put GPS instruments kind of everywhere on the plate boundary, InSAR where we have satellite-based maps of deformation—it's a real revolution! The hints that I was referring to are actually offshore slow motion, so you actually need to get the instrumentation under the water for these really big earthquakes, like really significantly under the water and a lot of it. There's real reason to believe we weren't able to look at the right spots.
The other thing, what I was just saying about earthquake catalogs—earthquake catalogs used to cap out around 1,000 or tens of thousands. We now know that we can make a million-earthquake catalog, and when we do that, and we sort of upgrade our analytical tools to match, there is more signal there. There's more to look at. Hiroo Kanamori and I used to have a joke when I was a grad student about fruit flies. For a while, I had a picture of a fruit fly tacked up on my bulletin board. The joke is that genetics made great progress when you have these many, many generations of—short generations, and then you can start to do population statistics. You can't do statistics on individual events. It can't be done. Asking about predictability is a statistical question, so you need populations and you need to be able to capture seismicity rates. That's all about having fast generations and little events. As we have increased our technology to be able to capture little, teeny tiny earthquakes—the way earthquakes work is there are ten times as many magnitude threes as fours, and ten times as many fours as fives, et cetera, all the way up. The smaller you go, the better your statistics, the better your ability to look at rate changes, and it looks different.
ZIERLER: Given that the onus presumably here would be ultimately, to prove that you're right, predict the earthquake before it happens, when do you feel like you, your colleagues, the field, the technology, when will you get to that point where you can demonstrate actually, yeah, one is coming, and then, there it is?
BRODSKY: I am not saying that it will ever be done; I said that we should be studying it. I think that might have been part of the PTSD, is people were willing to put some numbers on that at some point in time. I would like to get to the point where I could give an answer to it is or is not predictable, whether or not we are actually predicting. My bar is kind of low. I do think if we had several decades of instrumentation, expansively over a subduction zone like Chile, and we let it sit there for an earthquake cycle—30 or 40 years at least—we would know the answer, given how many magnitude eights and stuff you have there.
ZIERLER: It's as much a philosophical question as a scientific one, which is why I love asking it. To the extent that we cannot yet predict earthquakes, what about the Earth itself? Do you think the Earth knows when an earthquake is going to happen?
BRODSKY: Well, of course that's the question. To me, that's the real scientific question; I don't think that that one's philosophical at all. I think that's where people come down on different sides of this problem, is when they think whether or not there's something fundamental in the system. I don't think it has been proven. I think people lean a lot on stuff like chaos theory without bothering to do the quantification that goes with chaos theory, so I think there's a certain amount of sloppy thinking there. I don't know. I simply don't know. That's what I want to know, and that's what I'm trying to carefully craft an agenda to do.
ZIERLER: The quantum revolution that we're in right now, from quantum sensors to the simulative possibilities of quantum computers, what factor do you think this will play ultimately in earthquake prediction?
ZIERLER: Because earthquakes are classical?
BRODSKY: I just don't see the connection.
ZIERLER: Interesting. Some people are excited about that. Where's the break for you?
BRODSKY: Maybe I don't know enough about quantum computing, but I don't see why that would be relevant.
ZIERLER: What are some of the things that your graduate students are working on right now that might give a window into the future of the field?
BRODSKY: I just told you about RECAST which is this machine learning piece. I'm very interested in trying to quantify how the Earth organizes itself into a particular distribution of stresses, a particular arrangement of stresses on faults, and what that means about triggering and initiation. I have a student working on that, that I just mentioned to you. Will, who popped in at the beginning of this conversation—by the way, also, he was a Caltech undergrad—he is working on an analog system in the lab where we are able to fully image a whole sequence of ruptures. It's a nice soft system. It's like looking at a fault and being able to see how they all interact. I do think that sort of approach, again, we're going to be able to say what-causes-what-causes-what in this. I hate using the phrase, because it kind of is poison, but some sort of self-organization criticality going on there and trying to understand it at that level is an important part of it.
Another piece of that is understanding the scale-dependent strength of the crust. What is the failure strength of faults? I've just given you a lot of stories about the loading stress. In some simplified form, the earthquake problem is about loading stress and failure strength and when do they meet? I'm doing a bunch of stuff on trying to understand what the strength of the crust is at the scale of the crust. Most of what we know about the strength of the crust is from laboratory experiments about yea big. A lot of the work I've done on fault roughness sort of leads in that direction, looking at fault exposures and the topography of a fault surface, and asking what information is contained into that, in that wear scar, about the process that made the wear, and if it's making wear, that's making it fail, and that's the strength, right? [laughs] That's the logic. We've done a ton of stuff of going out and looking at faults and measuring the topography at various scales. We have an indenter in the lab and now we measure strength at various scales and try to make those two datasets talk to each other. Valere Lambert, who actually is also a Caltech alum, who is now my postdoc, is working on building up some theory to connect those two pieces of information.
Ricky Garza-Giron, who has no Caltech affiliation, just graduated, and he has been working on amplifying earthquake catalogs specifically during big volcanic eruptions. This is a different problem, but there are some related issues. I've been doing a certain amount of work on volcano predictability as well, which is in some sense an easier problem. Eruptions are known to be predictable at least in certain circumstances. What he's actually doing is looking co-eruptively. We have historically been totally blind during an eruption, because there's shit coming out of the ground and a lot of seismic noise. What he has been doing is using modern methods to extend our earthquake catalog, get all those little guys I keep talking about and look at seismicity rates during an eruption. That helps us understand how it opens and closes repeatedly. Earthquakes anti-correlate with when shit comes out of the ground. It's building up pressure and it makes earthquakes and then releases its cap. I think that is a big future of volcanology is these high-resolution methods.
Heather Shaddox just graduated, and what we had been working on was using seismology to look at non-earthquake signals, in particular oceanic internal waves, which also load the ground. Those, it turns out that you can look at island stations to learn about this oceanic signal, which is a pretty important signal for—internal waves are thought to play a big role in transport of both energy and mass and nutrients in the ocean, and it's possible that their behavior is changing with climate change, and so we're opening up this idea of using seismology in a historical sense, because seismometers have been there for a while, to look at climate change. That sort of bleeds into a sideline over the years, which has been environmental seismology. I think that's a bit of a growth industry, where we use the fact that lots of things pound on the Earth—rivers and glaciers and landslides—to say something about those processes. I've had students do that over the years.
We've done a bunch of fluvial seismology. The glacier stuff has been really fun. Some of the glaciers, the big ones—Whillans Ice Stream—is like an earthquake but better, because it does slip at its base, and you're only 800 meters away, so you can actually see it happen. A former student and I recently published a paper where we could really see the preparatory process. Those are predictable. I don't know whether or not real earthquakes are predictable, but Whillans Ice Stream things are predictable, and you can really watch the slow slip events migrating in. There's an interesting analog between that and the subduction zone stuff.
ZIERLER: In aggregate, what I'm hearing is that the field is vibrant and multidisciplinary and there's a lot of exciting stuff to do.
BRODSKY: Yes, right. I think you wanted to talk about Caltech eventually, so maybe I should stop there.
ZIERLER: No, that's great. It's just wonderful to hear. A science communication question—given that you have written for or have been profiled in a lot of national media outlets, what have you learned that's most effective? Obviously the public wants to hear eventually that earthquakes are predictable. How do you manage those expectations given that you retain some sense of optimism that that's something at least worth pursuing?
BRODSKY: Carefully. I think you treat people as intelligent people and you tap into what they already know. If it's anything one-on-one or with anything live where there's any feedback whatsoever, you check in with what they know and what they think. That's extremely effective. It's effective in teaching, it's effective in any form of communication, to make sure that you're having a conversation and not monologuing. In general, most people are cognizant of the fact that they want earthquakes to be predictable, and most people are cognizant of the fact that they have been told it's impossible. You acknowledge that they already know both of those realities. Once you've got it on the same page, you can carefully say, "These are the reasons I'm a little optimistic" and they'll hear it. You want to first ground yourself in what they already know.
ZIERLER: Between the AGU and the GSA, SCEC, IRIS, what are the scientific societies or groups that are really important for you in terms of getting the research done?
BRODSKY: There's a question I didn't expect! IRIS and its successor is mission-critical. Having a consortium, community, public access, and instruments and observations—I'm an observational scientist and would cease to function without it. I said IRIS and its successor because I'm including UNAVCO with that, which is the geodetic half of it. I take AGU for granted, as a meeting. I guess maybe we don't take anything for granted after the pandemic, but I would think we would suffer if we didn't have an annual meeting, where people actually knew that they could see—well, we have suffered over the last couple years. As I try to create something new with SZ4D. NSF. NSF is a kind of special agency. I go internationally, and different people's agencies work really differently. NSF, it's far from perfect, but it's a lot closer to perfect than what a lot of countries have to work with.
Geophysics at Harvard
ZIERLER: Let's go back now and establish some context before you get to Caltech. At Harvard, were you interested in geophysics and seismology? Was that already where you were headed?
BRODSKY: Geophysics, yes; seismology, no. I discovered geophysics my second year there, after a cross-country road trip when I was recovering from being a math major. I had some extremely good mentors at Harvard and I was interested in fluid dynamics. I spent a lot of time in engineering with Howard Stone. I was interested in dynamics. I went to Caltech saying I would do anything but seismology, which, you know, had foreseeable consequences. But no, I thought wiggly lines were boring and kind of dry. My friend Mia Ichihara was a postdoc at Caltech when I was a grad student, and she's Japanese, and she said, "Seismograms are a little bit like Asian calligraphy. You have to get your eye in. [laughs] Once you can see it, they're beautiful things! But it takes a long time to get your eye in."
ZIERLER: When it was time to apply to graduate school, where were you looking?
BRODSKY: I was looking at Caltech and MIT, and I guess I looked at Hopkins also. I thought I wanted to be a volcanologist. I guess that was the other thing that was going on then. I was looking specifically at a particular volcanologist at Hopkins. I basically went where Rick—Rick O'Connell was also my undergrad mentor—Rick and Howard told me to apply, because that's I think what undergrads do. I looked at Stanford as well.
ZIERLER: Why ultimately Caltech? What was most compelling to you?
BRODSKY: I decided at some point in the process that I needed to move west, that that's where geology was happening, and I needed to see some rocks, and the East Coast was not where it was happening. I think there was a certain amount of I grew up on the East Coast and I was ready to move away, 3,000 miles away. The last contender was the joint program between MIT and Woods Hole. That was sort of an exciting place at the time. I then came out and visited. I had a great visit. I had a very unusual class at Caltech, and I'm sure we'll get there, and that was the one and only year, I think, to the best of my knowledge, that they ran a field trip to recruit people. It was a great field trip. Lee Silver ran it. I think they had had a bust the year before on recruitment, and so they decided to get their act together and recruit. They ran this field trip, and I stayed friends with some of those people from that field trip—all of us who went on the field trip except for one ended up enrolling. Then I went to Stanford, and I saw a bunch of extremely unhappy grad students, so that wasn't going to happen. That was the decision.
ZIERLER: What year did you arrive at Caltech?
ZIERLER: Was it the Seismo Lab specifically that you went to, or was it more generally GPS and you wanted to see what was happening across the Division?
BRODSKY: I think I was more generally GPS. They put me in the Seismo Lab because I think they knew me better than I knew me at that point in time, but as I was saying, I wanted to study volcanology. I was told by various people that they were incredibly confused by my application, because they were going to admit me but they absolutely couldn't figure out where I fit because they didn't have many volcanologists, and I went through this whole application about how I wanted to do volcanology! [laughs] They stuck me in the Seismo Lab, but particularly my first year, I spent a lot of time going and hanging out with the petrology group, Ed Stolper's group, and went to their group meetings regularly, and then eventually decided I was not in fact a petrologist.
ZIERLER: I've had the privilege of talking to some of the first women graduate students in the Seismo Lab from the 1970s and 1980s. What was the gender balance when you arrived? Were women still in the distinct minority, or had it gotten better by that point?
BRODSKY: My class was the year it changed. We were totally equally split in my class. In fact, possibly we were slightly majority women. I came in with this very large class; there were 19 of us, GPS-wide. In the Seismo Lab, it was Magali, Jane, Debbie Smith, me, and Leo Eisner, and I guess Mark Benthian for like half a sec, before he left. That left four women and a guy. It was sort of different at the moment I arrived. We had an extremely tight class, socially, and again GPS-wide. Although I am told by older alum about all sorts of things, and even some of my contemporaries felt things, I never felt a problem. That's me.
ZIERLER: That's wonderful. A lot of hard work was done to get up to that moment.
BRODSKY: Exactly. I think that's a good way to put it.
ZIERLER: From that broad tour of GPS initially, what about JPL? Were you interested in what was happening at JPL? Was that relevant at all for you at that time?
BRODSKY: JPL was not really part of my world view. I had friends who worked at JPL. I knew about it because socially, people were involved. But no, JPL was a blind spot for me.
ZIERLER: After petrology, how did you focus in on the Seismo Lab?
BRODSKY: Oh, that was all about individuals. I was a devotee of Seismo Coffee. I went twice a day when I was up early enough in the morning, definitely once a day when it was in the afternoon. I still do Seismo Coffee with my group here. I think we're the last ones standing. I don't think Caltech does it anymore, but that's where I was right before I came here. At 10:00 every day, we have coffee together and talk science. We did it on Zoom all the way through the pandemic. I started through those coffees a conversation—when I arrived, Brad Sturtevant, who was in Engineering, and Hiroo, had a project for me on earthquake triggering and the fluid dynamics involved. They wanted to build on my fluid—and Brad was as close to a volcanologist as Caltech had, so that was their solution to the "Emily wants to be a volcanologist" problem. They got Brad and Hiroo together, and that was my first project. Actually my first paper was weirdly a lab paper with shock tubes with Brad. I started out primarily working with Brad and happily working on volcanoes. I went to volcano meetings. Hiroo, with a great deal of patience that I appreciate more in hindsight, just kept talking to me. [laughs] We just kept talking. I would always drop by his office with some sort of idea or something around 5:00 in the afternoon. Now that I'm a grownup, I realize how absolutely annoying that must have been! [laughs]
ZIERLER: [laughs] He's a very, very nice person.
BRODSKY: He is! It didn't seem to bother him that 5:00 in the afternoon was the time that Emily would wander in and want to chat for an hour. I would leave stuff in his box at night, and he'd come in very early in the morning. I worked until 1:00 or 2:00 in the morning; I'm pretty nocturnal and was very nocturnal as a grad student. Then he'd come in. So, we'd sort of have a 24-hour cycle going. That was so much fun that by year three, I finally admitted, "I think my advisor might be Hiroo. And I think I might even be a seismologist!" But it took about three years to get there.
ZIERLER: I've heard stories from the Frank Press years where the Seismo Lab thought of itself and was widely regarded as sort of the center of the universe for seismology. Did that feeling, whether deserved or not, stay with the Seismo Lab when you were a graduate student?
BRODSKY: Oh yeah, they were sure they were the center of the universe. They still are sure they're the center of the universe. I think that was my learning curve when I left the Seismo Lab, was to understand that they were not in fact the center of the universe. There was a very steep learning curve when I figured that out after I left.
ZIERLER: Fifty or sixty years ago, a lot of that had to do with the proprietary nature of data, that the Seismo Lab simply had stuff that no one else did. By the time you were there, was seismology and geophysics sufficiently connected enough where that was no longer the case?
ZIERLER: Then how would it have made the case that it was so central, in other words?
BRODSKY: I think you'll have to ask someone else that question. They just thought they were smarter than everyone else!
ZIERLER: What was Hiroo working on, at the time you connected?
BRODSKY: Hiroo always introduced himself in an interesting way that I think I've somewhat inherited. He said, "Oh, I'm working on whatever my students are working on." He would never tell me what he was working on. In a lot of ways, I pieced together his intellectual trajectory much later. When I was a grad student, I was very unaware of his intellectual trajectory. For instance, only in the last few years did I understand quite how preoccupied he was with earthquake prediction. I didn't understand that as a graduate student, because he had just gotten over it by the time I was there. What he was working on when I showed up I think was more or less a lot of stuff on earthquake scaling and radiated energy. That's what he worked on with Anu Venkataraman. I don't know if you're talking to her. He was gearing up on the early warning stuff, and he just had built out the TERRAscope network and was interested in using that data and how that could be used for making shake maps and those sorts of things. He's so curious and it never bothered him that I wasn't necessarily working on what he was already working on. That was a non-issue.
ZIERLER: It was more an interpersonal connection? You worked well together?
ZIERLER: What were some of the big debates that were happening in the Lab at that point? What were people excited about?
BRODSKY: There was the constant conversation about earthquake energy budgets. When I went back to visit ten years later, they were still having the conversation.
ZIERLER: What were people talking about?
BRODSKY: You draw a triangle and you figure out whether or not there's absolute complete stress drop or not, and where all the energy goes in the earthquake, and how that constrains the physics. I suppose there's a line to be drawn from that to my work on earthquake friction and taking the temperature on the fault. There's a very direct line.
ZIERLER: Please, explain it. What is the line?
BRODSKY: It's the same problem. Looking at the energy balance of an earthquake is something that can turn the forces and processes into something observable. The problem with the energy balance on earthquakes specifically has to do with what the absolute stress is on the fault, that the total elastic energy to be expended depends on the absolute level of stress. If it's high stress, you have a lot more energy available to you than if it's low stress. The seismological observations can't tell you the absolute level of it. The seismology tells you about stress changes. You bang on a table; it's the stress change that makes the waves. If you press slowly, if you just put a quasi-static weight on it, that doesn't make any seismic waves. I was Hiroo's student who studied earthquakes by not doing seismology. That's I think maybe my claim to fame.
BRODSKY: I do seismology, but it's not my focus. I'm not sure if any of his other students really went there. I think I realized from the infinite loop of the energy balance conversations that this was not going to be a problem solved by seismology and that one needed a larger set of tools in one's repertoire. Maybe a little bit of that was my initial reticence to even do seismology in the first place.
ZIERLER: Did you see that as an opportunity? That's where you could slot in.
BRODSKY: Yeah. I'm not sure if was a fully conscious decision, but I think it came from sort of my iconoclastic instincts that I never really wanted to be a seismologist, and so this was something I could do and not be a seismologist. I don't think that was a fully articulated thought at the time, but there is a line to be drawn from my emotional reactions to those conversations and what I ended up doing.
ZIERLER: What field work or observational work was most important for your thesis research?
BRODSKY: None. Field work, I did sort of recreationally as a grad student. I went and volunteered myself to do a field deployment at Long Valley with some USGS people, which was kind of a miserable experience, but got me out and about and learning stuff. I did something similar going to Kamchatka with a bunch of people I met at a meeting. I took a gravimeter and tagged along. I also learned a ton, but none of it made it to my thesis. All of that was intellectually valuable. Possibly the most formative thing was fairly late. Actually, three things. Fairly late in my grad career, we were starting to get very interested in dissipation on faults and the width of the dissipative zone, and I guess Hiroo had just done a paper with Don Anderson about the Bolivia earthquake dissipation. All of that revolved around how thick the fault zone was. Hiroo was starting to talk to some geologists, and we got Fred Chester out and gave us all a field trip to the Punchbowl Fault, which was actually a place I had gone. In my second year of grad school, I decided to take an intro mapping geology course. It was an undergrad course. None of the Seismo Lab advisors—Mike Gurnis said, "Why are you doing this?" [laughs] They all thought it was a crazy thing to do, but I thought I needed to go learn something about rocks, and so I went and did that.
That turned out—where Barclay took us on that trip turned out to be the same locality that we went back to for this field trip later for the Punchbowl Fault. I remember sort of standing there with Hiroo and with Brad looking at this fault in the field and just sort of starting to understand what it is you can learn from rocks about process. I think that was actually quite influential. I think having done that field mapping class was quite influential with Barclay. I think he has the honor of being the only person I've ever talked about thermodynamics with before 8:00 a.m. in the morning.
ZIERLER: [laughs] That's rare company.
BRODSKY: It is rare company! Barclay was great. What other observations were influential? It's a very interesting question. The Chi-Chi earthquake was very influential, which happened right towards the end.
ZIERLER: Why? What was it about it?
BRODSKY: That it had this difference in ground shaking. There was a difference in how the high frequency and low frequency behaved in that earthquake in the north and the southern end of the fault, and it was potentially very well instrumented with strong ground motion stations. That's when I started to understand how to put together—I guess the earthquake happened in September of 1999. The 21st, right?
BRODSKY: That's interesting. I guess I hadn't quite put together the timing. It must have been right when I got back from Kamchatka, because I was in Kamchatka in September of 1999. I guess the İzmit earthquake—1999 was an important year for me [laughs]—was that year as well. The İzmit earthquake was my first "I'm going to just run after this earthquake and understand it and look at the dynamic triggering in Greece." Luis Rivera introduced me over email to some guy who I, to this day, have never met, in the Geological Survey equivalent in Greece, the Seismic Network. We did a paper together on how the Turkish earthquake triggered earthquakes in Greece. That was the first time I ran after an earthquake and found the story in it.
Then Chi-Chi happened. At that time, I was spinning up on this story about hydrodynamic lubrication of faults with Brad and Hiroo, which was in some sense a continuity of my undergrad, thinking about how viscous flows work, and my wanting to be a fluid dynamicist and thinking about the lubrication physics of how a gouge might behave inside a fault zone. I had come up with a theoretical framework of how this would work, but I really didn't understand how to hook it into observations. I could hook it into maybe some geological observations, but I was sort of stuck on how to make an observational test of it. Chi-Chi had this difference in how the fault—where it slipped a lot, the ground shaking was actually quite moderate, the high-frequency ground shaking. And the opposite—and where it slipped less, it was much more chattering. That seemed to work well with this lubrication idea that where it slips a lot, then it becomes lubricated, the friction goes down, and it chatters less. That story was worked out partially when Hiroo's former student, Kuo-Fong Ma—who you should definitely talk to if you haven't already.
BRODSKY: She was—is—in Taiwan, and has done extremely well there. She came back right after Chi-Chi and came to Hiroo and said, "What should I do about this earthquake?" basically. She is very capable in a number of senses. Among them, she is the best diplomat I know. She at this point runs I don't know what swath of the scientific enterprise in Taiwan, but it's a big one. She's always my go-to on—even though we never overlapped at Caltech, but we got connected over Chi-Chi when she came back. She said, "What do I do about this?" I was walking down the hallway, and I think Hiroo practically, literally grabbed me and said, "Talk to Kuo-Fong." We sort of figured out this story about lubrication, which became a major part of the story of Chi-Chi. She started up a drilling project because she decided that to answer these questions, we really needed to go look at the fault. Then I got involved in that drilling project and that was my first drilling project. That involvement with Kuo-Fong—and Jim Mori got involved—was extremely instrumental in how I thought about things going further.
ZIERLER: What were some of the instruments, or broadly speaking the technology, that was most important for your thesis research?
BRODSKY: Technology? Just having public data. It was still a new thing, then, that I could just sit at my computer and download the waveforms. That was life-changing.
ZIERLER: Where was the data coming from?
BRODSKY: The waveforms came from IRIS for the most part. The catalogs at that point in time were more or less being composited by Berkeley. The data—the instruments were everywhere, from a whole bunch of regional networks and the Global Seismic Network.
ZIERLER: The laboratory experience that you have now, to some degree, that was not really part of your research?
BRODSKY: No, that came much later. Much later.
ZIERLER: What is the origin story of that? Was there a seed planted in you at Caltech where you realized you wanted to be more involved in a laboratory setting?
BRODSKY: [laughs] Maybe. My first project actually was a lab project. They tried to make a laboratory experimentalist out of me. I went over to Brad's lab and was sort of the lab assistant on these shock tube experiments to look at rapid degassing explosions. The experiments were water and CO2 in a shock tube, and then you popped it and you degassed it and took a high-speed movie, which in those days was a high-speed film camera, and we projected it on the wall. My job was to trace around the little blobs of fluid on the piece of paper as we projected it on the wall! We did it frame by frame and measured the speed, I kid you not! [laughs] It worked. I think that did sort of plant a seed of experimental work, but I was not lab-comfortable. I learned over time that that's a common issue, is that people who simply are just too uncomfortable with screwing around with stuff in the lab, that that is a barrier. They really wanted me to do more lab work than I did. When did I start really doing lab stuff? Two years ago, to some extent. Where did that come from? I think eventually I just wanted to answer questions. I got annoyed by being dependent on other people's labs. I kept wanting to answer these experimental questions, and I kept running around to colleagues. I went through a phase where I was going to Penn State a lot to use Chris Marone's lab.
ZIERLER: What was happening there? What was his lab doing?
BRODSKY: He has a big Biax that's a rock mechanics lab, and so we did some experiments where we were looking at how seismic waves change the permeability of rocks, which was something that a previous student and I had figured out observationally. That was in a 2006 paper where we looked at the tidal response in wells and showed that regional earthquakes changed the permeability probably by the seismic waves pushing fluids in and out of wells and unclearing fractures. Then we wanted to understand the mechanics of that, so Chris offered his apparatus, and we did a bunch of experiments there. I did that for a while. Then eventually I got tired of running to Penn State to do experiments, and we got to the end of that train of thought for a while, and the end of the postdocs, and the postdoc moved here, because he liked it here better than Penn State.
It's the granular flow stuff that I guess really got me into the lab, which I guess was an outgrowth of the lubrication stuff. It's always about people. In the end, it's always about people. I think I share this with Hiroo—that I tend to be very influenced by whoever I am around at any moment in time, and open to being pushed in directions. At the beginning of my career, I was on the faculty at UCLA. There was somebody over at Engineering who had a rheometer and wanted to talk to me and do experiments. I think he was just casting around for a connection. I said, "Well, I did this lubrication stuff, and I always thought maybe the gouge behaved like a fluid, but I was never really clear on what the right rheology of the gouge was, so why don't we do some experiments in your rheometer?" I think it was that. I think we were having lunch and we were all junior faculty together. He had worked with Howard before, and so somehow that endeared him to me. So, we did that. Those experiments turned out to be pretty interesting, so when I got here, I got a rheometer and started continuing that line of experiments. I guess Paul Johnson pushed me in that direction. Paul was at Los Alamos, and he was also interested in the connection between granular flow and fault gouge physics, and he had some resources to buy me a rheometer, basically, so he bought me a rheometer. Thank you very much, Paul. I still have it. We did a bunch of experiments together on that. Then that sort of started me off actually having a lab. It was a fairly small hobby, really I would say until two years ago. Now it's a hobby that has gotten a little out of control.
BRODSKY: That's sort of how I started having a lab. I just moved to a bigger room a couple years ago, and now it has expanded to fill the space.
Seismology at the Dawn of the Internet
ZIERLER: Having the internet—really one of, if not the first, academic generations in graduate school to have the internet—did that make your graduate research more sedentary than it otherwise would have been? Would you have done more field work if not for the ability to download data from wherever you wanted?
BRODSKY: Yes. It's interesting that you say that. I think that was the watershed of why we were doing things the way we were doing things, is we were suddenly—when I was a grad student, they were still trying to get us to work in the computer lab, because your desk didn't have a computer on it when I first got there. The computers were in the computer lab. I threw a temper tantrum at one point and said, "Actually, I'd like to work at my desk. Could I have a computer at my desk, please?" That was a novel concept and I think I was probably one of the first students in the lab to have a computer at my desk. Then of course everybody did. Then what happened immediately after that was that my hands went out, because the desks weren't built for computers. Nobody knew what we were doing to our bodies at that time. I went out, and then Sarah, Magali and Ben Weiss—I mean, we all went out one after another. All of our hands went. I road-tested the occupational therapists and then we all ended up going to the same PT. In retrospect, they totally didn't know how to treat it, either. They treated it like you had a hand injury and put me in splints, and I was trying to type in splints for a while, which made everything worse. No, there was a real change, and we didn't yet know even how to do it that way. It changed the kind of science we did. The fact that to me the resource was IRIS, not Caltech's network. And, it physically changed how we had to actually do stuff.
ZIERLER: What are the benefits and pitfalls, looking back? What did you gain from having all this ability to have data come to you, and what did you lose from not going out and doing more of the research yourself?
BRODSKY: I consider analyzing the data the research, so I would push back on that a little bit. That is the research.
ZIERLER: I mean just in terms of leaving Caltech, going out into the field.
BRODSKY: Right. I always kept going. As I said, I would volunteer myself for these things, and so even though that wasn't the data I ended up using, I got a fair amount of experience. I knew what a seismometer looked like, I knew what an installation looked like, and all of that. I don't think everybody did that. I do think, in terms of science, this ability to just reach out and grab data from anywhere in the world was transformative. That's part of why at least I could take the approach I always have, which is I'm just going to go follow the problems, and I don't need to have this sort of regional investment in a particular place or particular instrument. It gave me a ton of freedom. The internet is a good thing. What was lost? I don't know what was lost. I wasn't there beforehand to know. I'm sure something was lost, but it's hard for me to put my finger on it.
ZIERLER: What was Hiroo's style like as a mentor? Obviously you meshed wonderfully on an interpersonal level, but how hands-on was he in what you were doing?
BRODSKY: Oh, very skilled. I had two mentors. I had Brad and Hiroo, and it worked extremely well as a team. As far as Brad was concerned, everything I did was terrible, and as far as Hiroo was concerned, everything I did was perfect. I knew reality had to be somewhere in the middle! [laughs] He was definitely good cop. He was extremely enthusiastic and engaged in the science and willing to talk about it forever. The hours and hours and hours I have spent talking to Hiroo Kanamori, the amount of time we've talked about anything other than science has got to be like this much, so the interpersonal was scientific. I think he was very skillful. Now that I have advised for a lot of years, I can see what he was doing, but I didn't see it at the time. What he told me when I first started advising is, "Always encourage, never push." He actually said that to me, because I think he saw that I was pushing too much. That was very much the way he did it, is he would find something to encourage, and very gentle guiding.
ZIERLER: When did you know you had enough to defend?
ZIERLER: It's got to end sometime.
BRODSKY: This is a very funny story, actually; that's why I'm laughing. Because there was a moment. I was ready to go. I was ready. He wanted me to do one more project. He wanted me to work on this Nakajima sequence. It's kind of the only fight we ever had. We were kind of having a fight about it in August of 2000. And he went to visit the Pope. I don't know why he went to visit the Pope. Somebody—I think it must have been Enzo—somebody invited him to go visit the Pope, and so he went to visit the Pope. You ask him why he was visiting the Pope; I don't know why he was visiting the Pope. But he was away for a week! So, I took all my papers and I reformatted them and I stapled them together and he came back from the Pope and I'm like, "Here's the thesis! [laughs] I'm ready! I'm leaving!" [laughs]
BRODSKY: He really wanted that Nakajima stuff in there, and I thought—I was done.
ZIERLER: You put your foot down.
ZIERLER: Obviously, it worked out.
BRODSKY: It worked out okay.
ZIERLER: Who else was on your committee?
BRODSKY: That's complicated. My committee was Hiroo and Brad, and I guess originally Ed Stolper would have been the third. But Brad passed away a week before my defense. Do you know about Brad? You're the Caltech historian.
ZIERLER: Yeah, but please tell me how you heard of the news.
BRODSKY: Brad had cancer. He told me at the end of August, beginning of September, or somewhere around there, he was diagnosed that he had pancreatic cancer. I heard the news because he told me. He told me himself, in his office.
ZIERLER: Told you in the sense that he might not survive to the defense?
BRODSKY: He told me—can I remember his words? He told me he had pancreatic cancer. Oh, I do remember what he said. I said, "What am I going to do?" He goes, "Well, you're lucky you have two. It won't be a problem." That was the last time I saw him, because he declined very, very rapidly after that. I remember I was trying to see him or visit, and Carol just wasn't having any of it and wasn't interested, after that. Well, I guess I must have seen him one more time after he told me, because I remember him sort of looking aged over the course of a couple weeks. Like he had aged ten years over a couple weeks; I do remember that. Then he had passed away by early October. As I said, he passed away a week before my defense. Don Anderson substituted in at the last moment.
ZIERLER: What influence did Brad have on you? What lasted from your interactions with him?
BRODSKY: Quite a bit. Maybe that's where the experimental bug comes from? Who knows. Could be.
ZIERLER: That's kind of what I was thinking. That seems like that's the connection.
Good Science and Good Writing
BRODSKY: That could be! [laughs] That's fair. Brad worked on my writing. Oh my god, Brad had had it with my writing. That was some of the biggest fights we had, was over my writing. We would yell at each other. We would really scream at each other. He had a secretary sitting in his outer office, and she would just like cower. [laughs] She was like, "What's going on in there?" The biggest fight we had I think was over em dashes. You know the ones that have three?
BRODSKY: It was an issue! [laughs] I think I had sort of scooted through with being a pretty good writer up to that point, so nobody ever really took me to task, because I was good enough, and so they were working on the people who were not that good. He fixed my writing. A careful proofreader. He told me I was lazy, and I said I wasn't lazy. Anyhow! He made me into a careful proofreader and a much better writer.
ZIERLER: Writing matters, even for scientists.
BRODSKY: Especially for scientists! My mother always thought I was going to be a writer, and I tell her, "I am a writer. That is what I do for a living. I write!"
BRODSKY: At this point, I think I'm a pretty good writer. Brad definitely was influential in my writing. He said, "If you're going to go into a new field, you should have an unfair advantage." That was one of his statements.
ZIERLER: What do you think he meant by that? Just being ahead of the curve?
BRODSKY: I know exactly what he meant by it. He was this fluid dynamicist, shock wave guy, who went into volcanology.
ZIERLER: He could do things that no one else could.
BRODSKY: Exactly. That's a good way to enter a new field. I have pulled that trick repeatedly in my career, following his advice. That, I think, is what Brad gave me.
ZIERLER: By the time you defended, what opportunities were available to you? What were you looking at?
ZIERLER: Yeah, in terms of postdocs, faculty appointments.
BRODSKY: I had my NSF postdoc lined up with Michael Manga to go to Oregon, and so that's what I did right after. I defended in October, I hung out for a few months, and then I moved January 1st up to Oregon.
ZIERLER: What was compelling about Michael's group? What was happening there?
BRODSKY: Michael had been after me for a few years. I had known him from when he was a grad student at Harvard when I was an undergrad, so we knew each other. He just kept talking to me at various meetings, and sort of had been very interested in this fluids and faulting thing, and what you could tell from hydrological systems about earthquakes. I had started getting into that problem as a grad student. Hiroo must have given me this. I can't believe I can just put my hand out quite that quickly still. "Notes …"—this is my grad student handwriting. There was this sort of funny little thing from RPI. Hiroo must have given this to me, a technical report from 1964 about water wells used as seismometers for earthquakes and explosion detection. That's fine; this was Hiroo's fault. He had gotten me interested in the water well and earthquake problem, and that was also my first trip to Japan. I'm going backwards in time. He had gone to some review panel or other and was talking to his friend Wakita-sensei, who was about to retire, because they had mandatory retirement—and still do, but it was younger than—in Japan. He was an expert in looking at water wells and earthquakes. Hiroo was very interested in this as an underutilized observation. I got very interested in it, in grad school, although I didn't really do anything about it until later. But Hiroo certainly pushed me down that road. No, he didn't push; he encouraged. Hiroo was telling him he had this great grad student who was interested in these problems, and Wakita was like, "Well, let me invite her over."
It was this bizarre trip where I was invited right before his retirement. I suspect he was just burning his money at the end of his projects. I was invited to go absorb his knowledge like literally a couple weeks before his retirement. I went and visited the lab. I got this big tour of what they were doing in the lab. Then we went and did some field work. I tagged along on some field work on the Izu Peninsula, got shown all these water wells. I had never been in Japan before. That was an extremely influential trip. I got interested in what you could do on water chemistry and water wells in studying earthquakes. That led to all the permeability enhancement stuff.
Then I was telling Michael about this over a succession of AGUs. I guess my NSF proposal was actually to do volcanology with him. That's what it was. Sorry, I think I figured out what happened. I still wanted to be a volcanologist, and Michael was willing to tell me I was still going to be a volcanologist. Nobody else would lie to me! [laughs] Michael said I was still going to be a volcanologist, and we were going to get together, and I was going to work with him and Kathy Cashman, and we were going to do volcanology in Oregon. I said, "Great, I'll come do a postdoc with you." But he kept talking to me about the water well problem, and you know of course when I got there, I never did volcanology; I did water wells. That sort of started this hydrological earthquake thing that I think has been a huge part of what he has done since then.
ZIERLER: Including the fracking stuff?
BRODSKY: Fracking is a related phenomenon, but yeah, that included the permeability enhancement stuff. We wrote a paper together when I was a postdoc about a particular well in Oregon that sort of spun up that field, where you could look at and analyze the reaction of the water well to the seismogram because they're both at very high resolution, this high-frequency water well data, and you can see the response to the seismic wave change in the middle of the waveform. That's what started this whole permeability enhancement thing.
Yeah, he told me I was going to become a volcanologist and we were going to work on volcanology together, and so I went to Oregon to work on volcanology, and then as soon as I got there, he took the job at Berkeley, so then I applied for and got the Miller Fellowship, and then we all moved to Berkeley six months later. That's how that worked. I was only at Oregon for six months, but it was a good six months. Then I was at Berkeley for another seven months. I was planning to be there for three years, but then 9/11 happened. My now-husband, then-fiancé, was working at Ames, but he had an external fellowship, and he's British, and the way that all shook down was he lost access to the facility after 9/11. We all tried to explain that we were all bombing the same people together, but that explanation didn't fly, and British citizens or any other non-U.S. were not allowed in the facility, so he effectively lost his job. I already had the offer from UCLA at that point. I had been planning on not taking the offer, because they had not come through with anything for him. I was perfectly happy with the Miller Fellowship. But we very quickly, like over the course of a couple weeks, decided to move to UCLA, and so we did that.
ZIERLER: What's the takeaway, even the poetic takeaway, of starting at Caltech and thinking you were pursuing volcanology and then jumping right back into it for your postdoc?
BRODSKY: I wanted to be a volcanologist! [laughs]
ZIERLER: Caltech was just holding you back the whole time.
BRODSKY: Well, I can't blame them, because I'm still studying earthquakes now, so I don't think it was necessarily a problem. There's only so much they can take the blame for.
ZIERLER: To go back to that formative advice from Brad about being ahead of the curve, did you see that to be the case based on your education at Caltech and what you pursued afterwards?
BRODSKY: Yes. I have good fundamentals, and I am very comfortable with observations and uncertainty, and those have served me well.
ZIERLER: When you got to Oregon and then all of the institutions afterward, to go back to that very interesting thing you said about Caltech Seismo Lab thinking it's the center of the universe, did you think that in real time, or that's more of a retrospective comment that you can only make based on being elsewhere and looking back?
BRODSKY: That is retrospective. I certainly didn't understand that at the time.
ZIERLER: My last question goes back to the previous one, which is what did you learn at Caltech, the style of doing the science, the way of interacting with your colleagues, that stayed with you ever since and has made possible so many of the things that you've gone on to accomplish?
BRODSKY: What did I learn? So many things. I learned to be careful. I don't think we talked about it much, but I think that is what I learned. I will lay that at Brad's door, and Hiroo's door, both of them.
ZIERLER: Careful in analyzing the data?
BRODSKY: Yes. And thinking, carefully. To be careful. I think I went in there with a lot of enthusiasm and some reasonable education before then, but I had not yet learned to be careful. That's just a personality thing, I think, by nature. I needed to be taught to be careful and to connect all my dots. I don't think I needed to be taught the value of going out and talking to people, but content-wise, I knew nothing. I had a lot of raw energy but I was sort of mushy when I got there. I wanted to be a volcanologist, and I didn't even really know what a volcanologist was! It's the rigor, it's being careful. I remember Hiroo saying, "The thing you knew least about when you got here was earthquakes." I didn't actually know anything about earthquakes. There is a style thing, obviously, that came out of it—the Seismo Coffee style and this highly interactive style of doing science. I may have gotten there on my own, I might have gotten there just wherever I went, but I think it certainly fostered it and helped it and encouraged that. I don't want to undersell the actual content of what I learned there, either.
ZIERLER: Emily, this has been a very fun and insightful conversation. Thank you so much.
BRODSKY: Oh, thank you.