 It's one o'clock on a Monday afternoon, so you must be watching Think Tech Hawaii Research in Manoa. I'm your host, Pete McGuinness-Mark, and today it's really a pleasure to welcome my good friend, Rhett Butler, who is a geophysicist at the Hawaii Institute of Geophysics at UH Manoa. Rhett, you're going to tell us about a detective story, I believe, because you investigate a seismologist and a geophysicist, you investigate tsunamis and their deposits, and we've got a fascinating tale today for the viewers, because apparently you've found this cold case out in Kauai, where you're actually looking at old deposits from tsunamis. So can you give us a little bit of background? Very quick background. This is the most recent chapter in this detective story. It started after Tohoku, where we had a huge tsunami and there's some concern about how big it could be in Hawaii, which then led to doing studies of the allusions and how big earthquakes you could get in the allusions. And then looking for, is there any evidence that we've had a truly great earthquake in the allusion, which then keys into, gee, the Kauai deposit? And of course, for our viewers who are not that familiar, Tohoku was the giant tsunami. In March 2011, magnitude 9 and 9.1. Just over six years ago, and here in Hawaii, it obviously was a big concern in case there was... Well, we're all coastline here. Yeah. So every time there's a tsunami, all the coasts get it. It's a serious issue in Hawaii. And I guess what you're trying to do, you obviously understand something about the Tohoku tsunami, but there must have been earlier tsunamis which affected the islands. And this is where the story leads into the days. Yeah, exactly. So literally, there's been about five or six really big ones in the last hundred years. But since in the last hundred years, we've had five magnitude 9 earthquakes, the truly great earthquakes that have huge tsunamis. You could expect that in the prior hundreds of years, there were previous events. But is there any evidence? So in studying the possibility of an elution event, we found a, not myself, but David Burney, who is co-author on all of this work, found a deposit in a sinkhole on Kauai. So a sinkhole is basically a limestone deposit that gets turned into a cave by flow of water and then eventually the roof collapses, fills up with sediments, and then people go in and do archeology to look for human evidence, floral fossils, things like that. And what I think you're saying is that this evidence that you have found gives some hint that it took place before Western contact. Yeah, it's around that time frame. If you do carbon-14 dating, in fact, let me step back one moment. So this sinkhole is basically, this was unexpected. So as they would excavate into it about six feet down, they found this one yard thick layer of beach cobbles and shells and beach sand and huge thick thing. And then when you look at the entire deposit at the bottom, it's like several shipping containers with material. Well, this particular place is a hundred yards from the beach. It's about 20 or 30 feet uphill. So it takes a huge wave to carry all that material all the way up and then into the actual sinkhole itself, which then gets covered up by regular rainfall and other stuff. But do you think you've found a unique locality or do we find all of the sediments? We know very little bit. We know very little about what we call paleo-sonami, which is prehistoric tsunami record in the islands itself. So this is actually the only site that we actually have really solid evidence for prior tsunamis hitting Hawaii prior to about 1850. So quite exciting. So you can date it, carbon-14 dating. Carbon-14 dating, as it turns out, is not very precise. I mean, it's as good as you can get with using carbon-14, but the uncertainty was about plus or minus 120 years, which you get in a 240-year window. So, well, it's hard to nail down what it could relate to at other places around the Pacific. So what we've followed up doing is working with Ken Rubin at the university to date the corals that were found in the tsunami deposit for two reasons. One, to make sure that it fit the carbon-14 dating, double corroboration. And two, to get a tighter range of ages that then you could compare around the Pacific to see what other events might be correlated with. So a giant tsunami like the one you think you've determined must have been circum-Pacific in its extent. Precisely. So we can do the modeling for the Tohoku event. And so we have a good idea knowing the size of the earthquake, how big the waves are going to be. So you can do the same thing for Alaska allusions to say, okay, if we have a big magnitude 9, 9 and a quarter event, how big is it down in Kauai? And as it turns out, it takes a really big event, about a 9 and a quarter, to get enough energy to put all that material in the sinkhole. Now we've been talking about Kauai, I believe we actually got an image of the field locality. Is that correct? Exactly. Maybe we can bring the first slide on them and we can take a look at what exactly we're looking at. Yeah, now this is from Google Maps and this is up elevated looking down at the sinkhole. And you can see in the distance, that's the beach and the water. And so like I say, it's about 100 meters up the hill and the two smaller pictures show if you stand above this and take pictures down into it, how, I mean, this is a large thing. And we're looking at the southeast and shore of Kauai. Right. And... So everything has to come from the distant ocean over this rim and then fill up this sinkhole to a foot of a yard, to a yard thick and then it was subsequently covered up. Why is this an unusual locality, presuming the tsunami affected all of the coastline around Kauai? Right, and I've been working with the USGS and others to try to do some tsunami reconnaissance on other beaches and parts of the island, but that's an ongoing project. You can see in this picture, on the right side there, those are people. So you get a size of the scale of the sinkhole. It's really a large feature, even though it's just a little dot on the corner of Kauai near Pauifu Beach. And when you talk about the sinkhole, this is a fairly rare landform here in Hawaii. Quite. And of course, the distance away from the coastline is critical because only a large giant wave would be strong enough to transport this amount. Correct, correct. In other words, you've got to have enough energy to get it, you know, like I say, 100 yards inland and up over the lip of this and then you have to... It's not just a thin little layer. This thing is a meter thick. And the sinkhole presumably was what stopped all the material flying back into the ocean. Yeah. Which is why you don't see it at Waikiki. Yeah, on a flood plain, the waves would come in, the waves would go out, they would pull off a lot of this stuff. Here it goes in and it can't really get out. Who made this discovery again? David Burney, who is the director of the National Tropical Botanical Garden on Kauai. And he was doing work looking for fossils of pollen and little botanical things to date when different materials came to Hawaii. And he was confronted with this incredible, what he called a major marine incursion layer with shells and things. It's not obvious how you could do this except all the beach cobbles and things you find obviously came from the beach. Well, how to get up here. You can come up with many theories, but the most self-consistent one is that it's caused by the sun. And of course native Hawaiians before Western contact would not have put this amount of material. No, it would be underwater. It would be underwater. In other words, where you find it is below the water table. And so for the ancient Hawaiians to fill this thing up just seems a little well, it's pushing it. But once again, unless you find additional evidence, you always have to corroborate things. So anyway, so we did the coral dating. And the interesting thing that really came out of it was we could tighten it down from being plus or minus about 250 years to about plus or minus 20 years. And that date was I believe was 1572 plus or minus about 20 years. And so then, well, what does that compare to? In other words, now we have a very tight date. And you look all the way around the Pacific. And you look at all the literature you can find on what tsunamis have been observed in that time interval. And we did a very, very comprehensive look from everything from Alaska to the Pacific Northwest, Chile, Japan. Which are all the places that we normally get concerned about a tsunami. And there's a big earthquake offshore. We worry about tsunamis being generated from Alaska and Chile. So you go through and you find out what correlates. And then you start looking at, well, could this have been a source, another source instead of the elution source? Or is the elution the best source? And the interesting thing that looking around the Pacific is, once again, there's always this plus or minus 100 year kind of uncertainty in carbon 14 dating. But the unique thing about one of the deposits in Japan is it has an actual historical record. And so that was significant. So there is in the history of Japan in 1586 the report of a tsunami that they call an orphan tsunami. In other words, there was not a local earthquake that caused it. So all of a sudden a tsunami comes in, they're all surprised, and they made a note of that, but they did not have a local earthquake to relate it to. Like Tohoku, big tsunami comes in. The ground shaking as well. It's obvious, and that's the way it is in most of Japan. Ground shaking, then there's a tsunami. Well, here was just the tsunami. And in about 1960, after the Great Chilean earthquake, which is a huge earthquake in Chile, was so large that it killed people actually all the way across the Pacific Ocean in Japan. And it made the Japanese start thinking, oh, there are other sources for these tsunamis. Now one of them has turned out they had a orphan tsunami in 1700, and when they carefully batch everything and look at the historical record and they look at the Pacific Northwest Coast, it turns out that it's almost certainly a major magnitude about nine earthquake that happened off the Oregon, Washington coast. On January 26th, 1700, you had the exact date because the Japanese haven't dated. And the Japanese records go back hundreds of years further than Hawaiian records or native records. They keep track of such things. And they put up monuments and they put stuff that set out there for hundreds of years. They have a very excellent historical background. The Chileans have a pretty good one too along the South American coast, where the Spanish had settled and they kept track of things. So we had an orphan tsunami that was the 1700 event. So we have the 1586 event. And so could our Aleutian event have caused the tsunami in 1586? The timing is right. So then you have to go through the modeling. You have to say, okay, how big an earthquake would it take to create the tsunami that we saw in Chile? As it turns out, if you just plug in the numbers we've been using for the Aleutian event that we've seen now in Kauai, you can predict the amplitudes are on the order of a meter or two, which is what they saw back in 1586. So it's consistency, but it's not proof. Part of the reason that it makes an interesting story is that in 1960, when they started once again, the Japanese started looking at tsunamis coming across the ocean and impacting them. At that time, the Japanese were then trying to match the orphan tsunamis with other tsunamis. And they basically took two observations that if you look in the records of the history of the Jesuits in Japan who transmitted their stories, their reports, they got written up into the history of Japan and these got incorporated into earthquake and tsunami records by the British and others. Let me interrupt you there, Rat, because we're getting close to the break. So let me remind all the viewers you're watching Think Tech Hawaii Research in Manoa. I'm your host, Pete McGinnis-Mark, and my guest today is my good friend, Rat Butler, from the Hawaii Institute of Geophysics and Planetology, and Rat is a geophysicist and a seismologist. And when we come back, Rat, I will be asking you some more specific questions about it. So we'll be back in about a minute. Hello, everyone. I'm DeSoto Brown, the co-host of Human Humane Architecture, which is seen on Think Tech Hawaii every other Tuesday at 4 p.m. And with the show's host, Martin Desbang, we discuss architecture here in the Hawaiian Islands and how it not only affects the way we live, but other aspects of our life, not only here in Hawaii, but nationally as well. So join us for Human Humane Architecture every other Tuesday at 4 p.m. on Think Tech Hawaii. And welcome back. You're watching Think Tech Hawaii Research in Mana. I'm your host, Pete McGinnis-Mark, and my guest today is Dr. Rat Butler, who's a geophysicist and a seismologist. And we've been hearing about this orphan tsunami back in the 16th century. And Rat, before we go much further, let's take a look at a slide you brought along which actually shows the deposits. So if we can go to the second slide, this will give the viewers and the listeners a bit of a better understanding of what it is we're looking at. So here, tell us what we're looking at. So in the upper right corner there is the bottom of the sinkhole, and there was an excavation right beside one of those caves about 10 feet, 12 feet down. Now you have to pump it out to actually get in there because it's below the water table. But Dr. Bernie was very gracious to do that. And if we shift now to the left, to the upper left slide, you can see, if you're down in this, and you can see water at the bottom there and the pump or whatever. Yeah, the hose is for the pump. David Bernie is there putting his hand showing the level where above it is basically red clays and different kinds of terrestrial deposits. But below it is this black layer of basalts and sand, black sand and shells. And so this thing is about a meter thick and it's six feet underground. So it's quite a unique deposit. Now if we go down to the lower pictures, these are just with a water bottle for size, water bottle for scale, yeah. And all these beach cobbles are all rounded so that they've been bashed around the beach. So they pull all these things out as well as lots of shells. And if we go to the right one, we can see some of the pieces of coral that were actually picked up in this deposit. So the basis for all the work is actually the tight dates we can get on that coral. And it's using really state-of-the-art techniques at the university to get the precision necessary to date these to that value. So in terms of the research being done at the university, it's not only somebody like yourself, a seismologist who's trying to infer what the strength of the tsunami wave was on the earthquake which produced it, but it also relies very heavily on this dating technique that will give you a precise, relatively precise plus or minus a few decades. I find getting a plus or minus 20-year date is extraordinary. It is remarkable given it's over 400 years ago. Basically they're counting atoms and doing the decay rate stuff. So this really has been a team effort. Is this the sort of thing which is commonly done or does UH have a unique combination of skills? It's relatively unique. There's a group in Germany that does some of this work and of course I chose to work with my UH colleagues. And I also involved David Walsh who's at the Pacific Tsunami Warning Center. He was very gracious to do some of the tsunami modeling necessary to prove the case here. So it's a team effort. I was going to mention the Tsunami Warning Center because clearly the general public have heard a lot of the advisories when we've had some of these recent tsunami warnings. And they are the experts as well. But getting more to sort of how this might impact the general public here in Hawaii. What's the point of this investigation apart from it's an interesting science sleuthing story? It is an interesting story and part of it is just the story. But, I mean, if you're trying to understand what the risk to Hawaii is to tsunamis you have to understand what we've experienced. Now we have good records of the 1950 Kamchatka events, 64 Alaska, et cetera, all of the recent stuff. When you go further back in the record, there is no record. So we've built tsunami evacuation maps that basically are good enough for the last 100 years. But the recognition of the Tohoku event is that you can get really large events that are unexpected. And so when you model those events, it's pretty clear that our evacuation zones had to be much larger for very large events. So the impact of this research is once again to try to really define how big an event we've seen in the past, how much run up could we get from modeling and to then working with the state civil defense to reevaluate the evacuation map such that we have something that's really state of the art compared even to the Western United States. And I presume you're studying the recurrence info how often do these really giant events? Yeah, I did a study with Neil Frazier and Will Templeton on the projected recurrence rate and it's about a 10% chance over the next 50 years in round numbers. So 90% chance, nothing, 10%? Nasty. And that's the really big ones. Yeah, these are the really big ones, right. Okay. And they have a huge impact on the islands because as I mentioned earlier, we are all coastline. So, you know, you go to California, yeah, the coast when I get here. You can just run inland. You move a kilometer inland. There's no effect whatsoever other than local beach stuff. Whereas in Hawaii, we're all... So why don't we see more historical or prehistoric evidence for these giant tsunamis then? Well, as you know, we have hurricanes, we have rain, wind, we have lots of stuff that erodes away evidence. So you have to go look around and that's what's been going on, looking in the various marshes around Oahu and on the big island and beginning to start dating these layers because it hasn't been done before. And so this has kind of precipitated a lot of interest in doing this background work to once again define how many tsunamis we've had in the past, how big they are, how extensive they are. And by looking around the Pacific, then that helps to constrain how large it is because something locally can be large and distantly very tiny. But if you can start seeing this all around the Pacific, you know, you're dealing with extremely large events. So as a seismic detective working on these cold cases, it now sounds as if you're getting experience on understanding where to actually look in order to build up this sort of sequence of events. An interesting twist in this is that after 1960, when the Japanese were looking at these orphan tsunamis, they said, well, this 1586 event, it's probably from South America also. And in 1586, there was an earthquake in Lima, Peru and they said, okay, it must be the same one. Even though the historical leads were different, that was obviously some error in the past. But you can actually now look at the data for that 1586 earthquake in Peru. Now, you don't have any seismometers, but you do know where the buildings fell down. And in the local publications, they say, you know, where the shaking was intense and where it was mild. And if you match that to recent earthquakes, you can show that that 1586 event in Peru was not big enough to actually cause the tsunami in Japan. Now, you've done this work in Hawaii, but do you have to then go around the Pacific Rim? You've mentioned the Aleutians as well as Chile. Yes. Does your own research actually take you to these more distant places, or can you, so if you use Hawaii, it's a calibration plan? Pretty much I use the excellent library at the university. Okay. Because now on the internet, you can look up everybody's papers and really catch up. So, I am not a geologist or a true paleo-synomy expert, but there are people that really are experts and you rely on their work, and you put that in the context of what we're studying here. So, no, I'm not traveling around the world. I've done enough of that. You're not doing more field work in the institutions in the middle of going through anything like that. Just the field work here on Oahu and the islands. Okay. But you've mentioned that, say, civil defense in Hawaii is starting to pay attention to this. Have you seen further field? I recall in the 2004 Indian Ocean tsunami, they started to become aware of the risks of these events, which may only occur once every few hundred to a thousand years, sort of thing. Is this a growing aspect of your field? Certainly the 2004 event in the Indian Ocean, the one that happened on the day after Christmas, Boxing Day, exactly, depending upon which time. And the Tohoku event in 2011 were both surprises in subtle ways, but they were not expected. And so it really taught us, the geophysical and seismological community, that our preconceived notions, even though they fit all the model data, we have to think a little bit bigger for the unexpected. And so both of those were unexpected and so we've had to ramp up what is possible in terms of how big an earthquake can be, whether you can get a truly great earthquake. Are there only specific places, or is it in general? And then trying to look at, from what evidence you can, what are the recurrences of this? I recall Gerard Frier, who worked at the tsunami warning center. There are specific ways of modeling the path of a tsunami when it's generated for the dilutions and that sort of thing. So the seafloor matters, you can focus things from the seafloor, it provides little channels. It actually makes a big effect. It's a wonderful detective story. It's definitely very interesting. Are there students being involved in this kind of work? Will Templeton, who's one of Kwak Fai Chung's students, helped very much with Neil and I on the estimation of risk and the probabilities. I wonder what skill sets they really need. He's now in graduate school up in Oregon. So do they need a mixture of skills, both understanding the field deposits, as well as doing the numerical modeling? Well, if you really want to enjoy it, you've got to kind of dip your fingers in all of it to pull it all together. Now, that means you don't know everything. You become a jack of many trades and maybe you're not the ace, but you've got a lot of aces you can talk to and work with. We both live here on Oahu in Hawaii and maybe every few years we hear the tsunami warnings going off trying to appreciate the magnitude of what events might actually be possible. We all live here. Your family's here and if you know something about this and you can learn something and share it and make perhaps people more safe and better risk reduction, of course you're going to do it to the state. And these events may occur thousands of miles away from where we live, right? Well, you know, for better or worse, being out in the middle of the North Pacific here, we are surrounded by earthquake zones and we get tsunamis from all directions. So we really are kind of the focal point. It's not the best place to be other than the humidity we have here. We hope at least we see them coming in the sense that... We at least have a little bit of warning because it takes a while for those waves to cross the ocean. So we're 18 hours from Chile, but we're only 4 and a half hours from the Aleutians. So you've got to be ready. I'm afraid we've run out of time, but thank you very much for appearing on today's show. As I said, it's a great detective story that you have with a lot of science but also real significance to the residents here on the Wahoo and Naval Islands, of course. It would also be effective. It's more interesting as a detective story. It's not just the science. It's how it all comes together. Unexpected. Thank you so much for appearing on the show. Let me just remind the viewers you've been watching Think Tech Kauai Research in Manoa. I'm your host, Pete McGinnis Mark and my guest today has been Dr. Rhett Butler, who's a geophysicist and a seismologist telling us all about this orphan tsunami from the 16th century. So thank you for watching and please come back at 1 o'clock and we'll have another show for you. Bye for now.