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MICHAEL DUNNE: I'm Michael Dunne. We've done several shows about the Cascadia subduction zone, the major seismic fault that could lead to a massive earthquake and tsunami in our region, since the publication of a very scary and provocative New Yorker article years ago about Cascadia, much of the Pacific Northwest and even the world has focused on its dangerous potential. Well, a new study based on decades of hypothesis and research suggests it could be much, much worse. Today, on the show, we talked to an Oregon State University professor who led a study that shows a real link between Cascadia and the famous and destructive fault to our south, the San Andreas The study shows the potential that seismic activity on one fault could influence the other, including a massive co joined quake that could devastate the entire west coast. Professor Chris Goldfinger, a marine and earthquake geologist with Oregon State University. Thanks for coming on and talking to us.
CHRIS GOLDFINGER: Thanks, Michael, thanks for having me.
MICHAEL DUNNE: Interesting study you've been a part of. I think if those of us in the Pacific Northwest were worried about one fault, the Cascadia Subduction Zone, you've given us potentially something else to worry about. Talk about what your study found.
CHRIS GOLDFINGER: Well, this is, this has been a long-term project that really started almost by accident in 1999 where we were off Southern Cascadia, taking some cores, and we made a little navigational error, and we wound up off the northern San Andreas Fault, which is just next door to the south. We took a core there and hoped it might, you know, lead to working on the San Andreas at some time in the future, and like most people, we, you know, treated the faults as separate entities that don't, you know, don't interact. And so, we worked on those for a number of years, and wrote in a couple of early papers on it. And then, and then, somewhere in the early 2000s we started to notice that the ages, the radio carbon ages of Cascadia earthquakes, were very similar to the radiocarbon ages of the Northern San Andreas earthquakes. And we started head scratching and wondering what, what kind of sense that could make and wasn't terribly obvious. But then we realized that maybe one fault was actually triggering the other fault. And so, we enter, you know, one fault transferring stress to another fault is a relatively new concept, less than 30 years old in geology. And, you know, we're still learning, since plate tectonics isn't that old at this stage, we're still learning big things. And so, that idea was, you know, floated around a bit, and we continued to work on it, and then we finally wrote a paper in 2008 which is now, you know, a long time ago, suggesting this hypothesis. And we worked with Roland Bergman at UC Berkeley, who did the modeling of how the stress would transfer from one to the other. And it turned out it was possible, but not, not very efficient, and not, not all that favorable, but possible and so, but at that time, we had only radiocarbon ages to compare the timings with. And radiocarbon, you know, is notoriously both useful and uncertain. So, the radiocarbon age of, you know, something several 100 years old, might have an uncertainty range of 150 to 250 years, or sometimes even bigger. So, while the most probable age isn't matched up pretty well, the uncertainty was large. So, you couldn't, you know that the smoking gun just wasn't there. And so, we wrote more proposals, and went out and collected more cores and continued on. And quite a few more years went by without, really, you know, with improving the data sets and improving all, every, every aspect of it, but, but without finding a, you know, a key link to how, you know, how can we test this hypothesis? And, but there was a thing, something that bugged us a great deal about these, these beds, they're called turbidites. They're submarine landslide deposits. And the thing that bugged us about them is the ones on San Andreas and Cascadia, or the faults that were close to each other and close to them. The boundary between the two faults at Cape Mendocino, they seem to be upside down. They had the sand at the top instead of the bottom where it normally belongs. And, and this is like, you know, imagine taking a, you know, a bucket full of sand at the beach and swirling it around and, and the sand should be at the bottom, but these, these beds had the sand at the top, and that bugged us for actually, quite a few years. And left the question open, you know what? What's causing this? And does it have any relationship to anything useful and, and so some sometime around mid, well, 2015, 16, somewhere in that timeframe, it dawned on us, and I'm not quite sure how this happened, but that we were looking at not one bed with the sand on top, but two beds, and the lower one was finer grained and the upper one was coarser grained. That's where the sand was. And so that explained it. You know, we gravity couldn't have switched signs and gone the other way during that time. So, we needed some explanation that worked, and that worked so two deposits instead of one, so that double decker turbidite bed. And then when that, when that idea occurred to us, then, then the dam broke open. Then we realized that, Oh, there's the smoking gun, right there you have these beds on top of each other, and they could represent Cascadia earthquakes and San Andreas earthquakes stacked together very closely. And in the case of, say, the well-known 1700 earthquake…
MICHAEL DUNNE: …on their Cascadia Subduction Zone, right?
CHRIS GOLDFINGER: Yeah, on the Cascadia Subduction Zone, which we know very well, and most people have heard about that on directly on top of it seemed to be a San Andreas earthquake that had that happened about the same time, around 1700 and these things were stacked so closely together that you couldn't distinguish the time between them. And that's sort of, that's sort of the short version of how this came about.
MICHAEL DUNNE: And when you say that potentially, that they're linked, does that? Does that mean that, you know, we always, someone like myself, thinks of a fault line as just that. Does that mean that the San Andreas Fault line and the Cascadia subduction fault line they intersect. Or is it, is it not as simple as that?
CHRIS GOLDFINGER: Well, it's, that's a great question. So, the Cascadia subduction zone ends at Cape Mendocino along another fault called the Mendocino fault, and the Santa San Andreas Fault comes up to, you know, in very close proximity to it. And then what physically happens is very unclear. Nobody's really sure exactly how they physically interact. And the latest studies suggest that the San Andreas may extend into the Cascadia Subduction Zone some distance past Eureka and up a little, maybe a little bit further north, and the geophysical and the GPS, evidence of what's actually moving suggests that, but physically how that happens, it really knows right now. And that's, that's, that's a topic of debate and future research.
MICHAEL DUNNE: I'm a native Californian, and I know the San Andreas Fault well, and certainly, if My memory and knowledge is correct, the San Andreas has had earthquakes on it much more recent than 1700s so I'm wondering in some of your research, did you find, I guess, famously, like the 1906 San Francisco earthquake, if my memory serves, that was a San Andreas Fault earthquake. Did you find evidence in a much, relatively more recent time like 1906 versus 1700 a relationship between San Andreas and Cascadia?
CHRIS GOLDFINGER: Yeah, great question. I'm also a native Californian. My grandma's house in Daly City was right, almost right on top of the San Andreas Oh, wow. Okay, so I'm very interested in both, you know, for that reason as well. But yes, so when we started working on the cores from the San Andreas area, and yes, we found, the first thing we found was, was the 1906 earthquake. It's very, very easily identifiable. It's traceable all the way from Cape Mendocino to San Francisco. And our cores, our cores go all the way, actually, to Monterey Bay. So, you know, in Paleo seismology, of course, if you go back to a historical earthquake, and you're proposing that the beds you're seeing are earthquakes, you definitely want to see a. Uh, historical earthquakes in the record, if, if you don't see them, then something's wrong, sure. And so, the 1906 earthquake was there. It wasn't the youngest event, though. It was overlain by 1992 and 1980 earthquakes that were actually on Cascadia, but close enough that they could deposit a bid at the northern end of the San Andreas Fault. So, we have three historical earthquakes that were recorded in that region. And so that really helps us in the confidence department. And in terms of, you know, are, what are we looking at? Are we really look, for sure, looking at earthquakes? And when we found that we had three historical events clearly in the record and datable to very tight timelines, then that lend a great deal of, you know, confidence into what we were doing.
MICHAEL DUNNE: I'm fascinated by how you conducted this study. Talk about the way in which you, you, you get these core samples?
CHRIS GOLDFINGER: Oh, well, this is sort of an industrial operation. We're using a ship that's about 270 feet long, and a crew of Science Party and ship’s crew of about 50 people, and we're taking them in water depths of around 3000 meters or so, sometimes a little bit more. And so, it's, yeah, it's an industrial operation where we're lowering this core coring device to the sea floor, and then it free falls, kind of like a lawn dart into the sea floor, and it collects a four-inch diameter sample, and we pull that back up to the surface, and we slice open the liner that it comes in. And then we start doing things like CT, scanning the core and collecting geophysical data from the core photo photography and magnetics and density and all those sorts of, these sorts of things. And then there, these cores are assembled and worked up and correlated from place to place in much the same way the oil industry correlates their core samples when they're looking for oil, they're also working with the same type of turbinates that we are.
MICHAEL DUNNE: What are the implications from your findings in terms of we, as I mentioned, you know, at the top, I think we're all very cognizant of the potential danger of the Cascadia subduction zone. What do your findings suggest about the potential, I guess, increase in veracity and power from an earthquake, if these two faults are linked?
CHRIS GOLDFINGER: Well, I think that if I can go back, if I can step back to talk about the timing between them, because the timing is an important feature of this whole story. If they're separated in time, then they just remain, you know, separate events. But in our case, we found evidence that these are fairly close in time, and that has big implications. So radio carbon doesn't really allow you to get close timing to within, you know, better than 50 years, or in a lot of cases, sometimes not as good as that. And so, what we use is called a relative dating technique, where we look at the timing between events to see what the separation and time is independent of, you know, the absolute timing that's available from, say, radio carbon. And so what we found was, for example, in our in our best example, the seven the famous 1700 Cascadia earthquake, which is known to have occurred on January 26 1700 that bed in on the Cascadia side in our samples, looks like it's directly overlain by the San Andreas earthquake that happened about the same time. But that bed was apparently laid down while the Cascadia bed was still depositing so that's telling us that the time frame is probably hours, potentially minutes, but probably hours to maybe a day or two at the most, at the very most. And so that gets us very close in time where radio carbon just gets us in the ballpark. And then we have two others that are similar to that very close timing, but absolute timing, you know, not as well known. The 1700 event is also supported by tree ring evidence. So, a group has worked on tree rings in Northern California, looking for the penultimate San Andreas earthquake. And they believe they found it. And they are there. There's a little ambiguity, but they think that the last earthquake was either 1698 AD or 1700 AD. And we think it's a 1700 option. And so that puts us in the same year using completely independent methods. So, to come back to the implications of it, of course, if they were decades apart, that would. Be quite different. But the potential is that these things, these earthquakes, could happen closer in time than that. And if that were to happen, and it seems to be that these timings are not or these pairings of these events are not a rare event, they seem to be actually the majority of the case, with 1906 being an exception. So, if that's the case, then you can imagine that we've talked for years and years about, you know, the quote, big one in Cascadia being a, you know, a major, you know, possibly the worst disaster in North American history. To borrow a phrase from, you know, The New Yorker article a few years back. And so, if that were the case, and then the San Andreas were to go in an earthquake that stretched to San Francisco in some short time frame, that would be huge, you know, in the draw, the draw down of the resources of the of the country to try to respond to two events like that and not one. It's difficult to imagine. We're having a hard time just imagining one of them, let alone two. So, it's, it's a, yeah, it's a significant thing that hasn't really been considered. Emergency Managers have not really considered this in any significant way. It's been discussed a few times in FEMA, and it's even in one of their documents, but I don't think it's really been taken very seriously up to now.
MICHAEL DUNNE: Okay, again, putting on my extremely amateur earthquake scientist hat, I've always heard that small earthquakes can be good because they can alleviate pressure. Is the potential linkage between San Andreas and Cascadia? Are there elements, and I think you've used the term sort of shared energy with regard to these two faults. Is it possible that a small earthquake on for example, the San Andreas Fault might help alleviate some pressure on Cascadia and vice versa?
CHRIS GOLDFINGER: Well, I wish that were the case, but it's probably not the case. So typically, if one fault has a major rupture, what it does is it relieves the local stress, but it transfers that stress to other segments of the same fault or other nearby faults. And it can transfer stress in in either increasing the load on those faults, or can actually sometimes decrease the load on those faults, just depending on the geometry so but relieving stress in that sense, is probably not going to be the case in the modeling that Roland Bergman did in our 2008 paper, we found that it would load parts of, you know, a Cascadia earthquake would stress parts of the San Andreas, and it Would de stress other parts of the San Andreas, but the key bit was near the very north end, where the rupture might begin. And so, you know how that actually works? Loops back to what we discussed about the geometry. We just don't know the geometry all that well, so modeling it is problematic. And so we're, you know, in this paper, we discuss just, just the strategy, stratigraphic evidence that it happened, exactly how it happened is, you know, a question yet to be resolved.
MICHAEL DUNNE: My last question for you may be, fall into that category too, but I, I am curious, as I understand it, one of the sorts of the holy grail of studying earthquakes is, is the idea of eventually getting to a place where we might be able to detect them before they actually occur. And I'm wondering in your study, is this linkage of such that, for example, if something were to happen in Cascadia, and knowing now this, this, this linkage, might it be that it would give us some time so that phone calls could be made to San Francisco saying, Oh, we're seeing this here, and it might be headed your way. Or maybe I'm obviously being too overly simplistic, but I'm just wondering if there's any, any benefit in this linkage towards detection.
CHRIS GOLDFINGER: Well, I Yes, I think, I think there is, and, you know, I've had my head down just working on the geology only, and the paper just came out. So, the implications of it are, you know, yet to be, yet to be thought through. But there is the possibility. And you mentioned things, you know, like early detection, or, you know, we in geology, the prediction is the P word, and we try to never even utter that word, because it's just not possible at present, sure, but if we have a lot of data that shows that. This linkage, this pairing, or synchronization of the faults, has gone on for a number of 1000s of years. Then you, you would have to say that if Cascadia had an earthquake, that the northern San Andreas, you know, could very well go within some time frame. And so, it's possible that Cascadia can serve as a natural warning for the northern San Andreas and the Bay Area. Now, the complexity of it is, you know what, if you have an indication of something that could happen, it could happen minutes from now, or months from now, or maybe a couple of decades from now, and you wouldn't know which you know, you know. And I don't think anyone has considered that possibility. What, what would you do with that information as a society? I really have no idea, but, but, but that's a secondary feature. The fact that it would act as a potential warning is a real thing, and it could potentially give much more, much more warning time than the current automated warning systems, which give you seconds to minutes, depending on you know your range and the type of earthquake.
MICHAEL DUNNE: Fascinating, fascinating professor, Chris Goldfinger, a marine and earthquake geologist with Oregon State University, really appreciate you coming on and talking about this fascinating subject.
CHRIS GOLDFINGER: Thank you for having me on, Michael.
MICHAEL DUNNE: That's the show for today. All episodes of Oregon On The Record are available as a podcast at KLCC.org. Tomorrow, on the show, we'll talk with a documentary film director who's put together a new movie about how indigenous people view Bigfoot, and it's strikingly different from what Western civilization has imagined and cultivated. The film just debuted at the Bend Film Festival, and it will be making the rounds throughout Oregon. I'm Michael Dunne, host of On The Record, thanks for listening.
