Kohtaro Ujiie

field geology, international cooperation, life onboard, Nankai Trough, JFAST, marine geology, Chikyu, JOIDES Resolution

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This transcript is based on a video-recorded interview deposited at MarE3, JAMSTEC (Yokosuka, Japan).

The transcripts of the research project Oral Histories of Scientific Ocean Drilling are polished representations of oral conversations, and are intended solely for the purpose of preserving and documenting personal accounts and memories. They are not a literary product, and are not intended to exhibit literary qualities.

The primary goal of this transcript is to capture the spoken words and memories of the interviewee as accurately as possible. Minor editing and polishing works have been performed to enhance clarity and readability while maintaining the authenticity of spoken discourse, including non-standard grammar, inconsistencies, repetitions, and pauses.

The reader must be aware that memories of an event can vary between individuals and may evolve over time due to various factors, such as subsequent experiences, interactions with others, and personal emotions.

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Please cite the interview as:

Interview of Kohtaro Ujiie by Beatriz Martinez-Rius on 2024 September 07, D/V Chikyu, Japan. [link]

Beatriz Martinez-Rius (BMR): Today is Sept 7 of 2024, I’m Beatriz Martinez-Rius, historian of science at JAMSTEC. I’m onboard Chikyu on Expedition 405 with Kohtaro Ujiie. Thank you.

Khotaro Ujiie (KU): Thank you.

BMR: Can you tell me your name, affiliation, and current position?

KU: I’m Kohtaro Ujiie, Professor at the University of Tsukuba, and I’m a specialist in structural geology and fault mechanics.

BMR: Please tell me about your background.

KU: My research is mainly to understand how slow and fast earthquakes occur in subduction zones. And I’d like to know the deformation processes and mechanisms of slow earthquake and fast earthquakes. The method is… field work in exhumed accretionary complexes and metamorphic rocks, laboratory experiments using fault zone material, and IODP cruises (drilling into the seismogenic zone).

BMR: How did you got interested in these topics?

KU: First of all, I got a PhD based on deformation and fluid processes in exhumed accretionary complexes. But when I finished my PhD – there’s a seismogenic zone located in the accretionary complex. At that period, the temperature conditions of the seismogenic zone were getting known, the knowledge on temperature conditions was improving, and we noticed that the seismogenic zone is located within accretionary complexes. In the future, we should focus on how and what deformation processes and mechanisms of the huge earthquakes in seismogenic zones. So it’s highly motivated.

BMR: And before that, what lead you to choose Earth Sciences?

KU: No specific reason… But I like the field, rather than lab experiments. Field studies attracted me because I could go outside.

BMR: I think that many people of this field come into it because they like hiking, or they like being outdoors…

KU: Yes, yes.

BMR: Was there any one during your undergraduate or PhD training that was influential for you? Some kind of mentor that drove you to this pathway?

KU:The previous president of JAMSTEC, Asahiko Taira. I read his book; the title is How the Japanese Islands Were Formed. The formation of the accretionary complex is the key to the formation of the Japanese islands. I became very much interested in accretionary complex. That’s one of the reasons why I chose accretionary complexes.

BMR: Have you worked with him?

KU: Yes, yes. Actually, when I was a postdoc, he invited me onboard as a structural geologist while he was co-chief of the Nankai Trough expedition. In ODP, before IODP. In the Ocean Drilling Project.

Kohtaro as a postdoc, working together with co-chief Asahiko Taira onboard the JOIDES Resolution, during Leg 190 to the Nankai Trough (2000). Left, Asahiko Taira, Kohtaro and Chris Fergusson (sedimentologist, Australia) taking notes about the just-recovered cores. Right, the day shift discussing together. Courtesy of IODP-USSO.

BMR: Actually I have interviewed Taria san for this project four times, I think he has been an influence or point of contact in this field for many people.

KU: Yes. This was an amazing expedition. There were famous researchers onboard, and I also made new friends, so many good friends.

BMR: Was this your first contact with scientific ocean drilling?

KU: The Nankai Trough leg? It was an ODP cruise, offshore Shikoku island. ODP Leg 190, yes.

BMR: Was this also your first international collaboration?

KU: Yes.

BMR: What kind of things do you remember about it?

KU: I was a little bit nervous, but also exited. Half and half. In less than one week, I got familiar with the life, the lifestyle onboard ODP.

Kohtaro participating in ODP Leg 190, aboard the JOIDES Resolution. Left, group photo of the day shift scientists, over a core from the decollement zone. Upper right, Kohtaro discussing with Chris Fergusson about the Site 1175 results. Lower right, Kohtaro teaching chopstick skills to the onboard scientists before the portcall in Yokohama. Courtesy of IODP-USSO.

BMR: How your involvement in scientific ocean drilling continued after that?

KU: When I attended to the ODP cruise, I was a postdoc, a JSPS (Japan Society for the Promotion of Science) postdoc fellow. Then, JAMSTEC invited me to be a researcher, and I moved to JAMSTEC as a researcher. Chikyu was then constructed, and I attended the first IODP cruise by Chikyu. Marianne (Connin), actually, she was in the first LWD (Logging While Drilling). She was in leg 314, and I attended leg 316.

BMR: At that time, you had been on board the JOIDES Resolution and then on board Chikyu. What kind of things surprised you or were different? What do you remember, of the first time you were on Chikyu?

KU: We obtained very good results. Before the Chikyu’s cruise, our objective was to characterize how seismic deformation occur through the fault, between the shallow portion of the mega-split fault and the plate boundary fault. Our result was that we found evidence of a co-seismic slip, even if it’s a very shallow portion. This was so surprising. Nobody expected such kind of result. And I conducted high-velocity friction experiment using the Nankai fault zone material got some mechanical data demonstrating earthquake rupture can propagate easily along shallow portion of the faults.

So, this leg of NanTroSEIZE was in Nankai Trough, as well as the ODP Leg you did in the nineties. Both were around ten year apart. What kind of differences in terms of science and technology you found? I’m asking about the development of the scientific knowledge in the area.

The ODP cruise was focused in deformation and fluid processes, at the toe of the accretionary complex. When I was a PhD student, I studied the exhumed accretionary complex called the Shimanto accretionary complex – on land analog of the Nankai Trough. I was studying the deformation and fluid processes. But I’d liked to see an active accretionary complex, so the ODP cruise was a very good chance for me to see an active accretionary processes. But Chikyu’s cruise was quite different than the ODP one. It was more focused on studying the seismogenic zone.

IODP Expedition 334 to Costa Rica’s seismogenic zone, in 2011. Left, Staff Scientists Nicole Stronick (left) with co-chief scientists Kohtaro Ujiie and Paola Vannucchi (University of Florence). Right, group photo of the scientific party on the JOIDES Resolution. Courtesy of IODP-USSO.

BMR: How many times more did you embark on Chikyu, in total?

KU: This time is the fourth.

BMR: So, two expeditions of the NanTroSEIZE Project?

KU: The first and final parts of NanTroSEIZE; so, IODP Expeditions 316 and 358.

BMR: So please, tell me about the J-FAST expedition. How did you got involved in that?

KU: Actually, before J-FAST, we made a kind of committee to assess whether such kind of fast drilling was feasible or not, and I was invited to present the results of fault rocks in Nankai Trough and friction experiments, which were performed as a structural geologist. Several people were invited from all over the world, and each of them had a different expertise. We had a 3-days meeting in Tokyo. And our decision was, that it was feasible and an important to detect the temperature. We also need to take samples from the seismogenic zone, which is actually located near the trench; so it was a good chance to drill into the seismogenic plate-boundary fault. And then, we decided to write a proposal and I wrote some part of it. And of course, I applied (to sail) at J-FAST.

BMR: You applied and became part of the scientific team.

KU: Yes, I attended as a leader of structural geologist.

Kohtaro during different IODP expeditions onboard Chikyu. Left, during Expedition 316 to the Nankai Trough. Right, Mariane Connin (University of Nancy), Kohtaro Ujiie and Jim Mori (Kyoto University) pointing to the portion of the plate boundary fault zone recovered during JFAST (IODP Expedition 343), in 2012. Both images, courtesy of JAMSTEC/IODP.

BMR: Now that you are co-chief, what are the differences between that time, when you were in the scientific party, and this time?

KU: A co-chief has many responsibilities… The other co-chiefs of this Expedition are excellent so… It will go well. We will have a nice expedition, I think.

BMR: I’m sure it will go well. Did you play any role in selecting the scientific party for this expedition?

KU: Yes, yes. This kind is part of the co-chiefs’ tasks.

BMR: What kind of things did you take into account in order to prepare the group, the team?

KU: We considered a lot of things. For example, diversity, nationality, experiences, and so on. And also, whether they are a new or younger generation. We thought about a lot of things, yes.

BMR: What other things did you do for preparing this expedition? I know that the preparation started some years ago, so what has been your involvement?

KU: This time, a difficult thing is that we have split the scientific party in two windows, and both need to communicate with each other very well. That’s a very important thing.

BMR: It’s nice that many people of the previous J-FAST expedition is participating onboard. So, what are your views on these 12 year period? What kind of relation have you kept with the shipboard scientists?

KU: As a co-chief, the important thing is that everybody can get samples for post-cruise research. And, of course, during the cruise hopefully everything should go well. Personally, I’m very much interested in healing processes. Actually, the J-TRACK proposal was approved for drilling more than 5 years ago, but we had to wait for a budget issue or the Covid issue. But, on the other hand, time has passed, which means that it has provided a good chance to examine healing processes.

If J-TRACK was held just five years after J-FAST, healing may not be expected. But, after more than ten years, we have a better chance to examine how healing processes occur. This is a very important, unresolved issue, to really understand how shallow slip occurs. We provided that co-seismic friction is very low. So, it facilitated the slip to the trench. But on the other hand, we don’t know whether large, shallow slip occur as a result of accumulated strain or just when the deeper portion ruptures, and propagates to the shallow portion. In this case, even the unstrained shallow portion could rupture associated with rupture progression from deeper portion… So, it’s a good opportunity to answer this. Personally I’ve prepared these two hypothesis and I’d like to answer them.

You mean that your hypothesis is about stress accumulation?

Yes, stress accumulation. We would like to know whether the locking of the plate boundary faults has already started, or is still unlocked.

BMR: According to your perspective, what role does international collaboration play in organizing and  running such a study?

KU: Actually, I collaborated with one of the shipboard scientists, and we plan to conduct long-term healing experiments. We’d like to construct an equation showing the relationship between healing rate against time. And then, we also calculated the accumulation of stress later, and compare it to when the next earthquake will occur. Or, continue to unlocking.

Kohtaro in the core lab during IODP Expedition 405, onboard Chikyu. Right, talking to geologist Cath Ross. ©️Doriane Letexier / JAMSTEC / IODP.

BMR: So, now I want to ask you about the future. This expedition has just started so we cannot think about the results, but what kind of things do you expect for the future of scientific ocean drilling?

KU: The results of this expedition are important for the Japanese people. This is not only important for science, but it’s also useful or informative from social point of view. Actually, I had an interview two days ago, and they always ask me, “Is your result useful for better understanding when the next earthquake will occur?” I always say that it’s difficult to predict. But, on the other hand, we need to explain what’s going on at the shallow plate boundary. So, we may say whether stress is now starting to accumulate or not. This could be important… So, the future IODP should do not only be curiosity-driven science, but also ready to communicate science with social importance.

BMR: In this sense, how has scientific ocean drilling changed throughout your career?

KU: More social relevance. And the key word would be geohazards. This means, not only focusing on the seismogenic zone but also including submarine landslides, and submarine volcanic activity… All of them, very important for society. We have had some domestic and international meetings about the future of the IODP, but unfortunately the US won’t be able to participate. So, it will mainly be based on Japan and ECORD.

BMR: Yes, it will be starting soon.

KU: Yes… This is actually last IODP cruise (laughs).

BMR: Actually, how do you feel about being a co-chief in the last IODP expedition?

KU: It is an amazing experience, yes.

BMR: Being the first and the last one, it’s something…

KU: Yes, yes; it’s something special.

BMR: Let me ask you one more question. What is the most valuable thing that you have learned or experienced in scientific ocean drilling in your career?

KU: I have learned a lot, from scientific ocean drilling. And it’s always surprising. Not only seismogenic-zone related stuff, but even during the ODP cruise, it was always surprising. We prepare a proposal and put together some hypothesis, but it’s usually wrong (laughs). And then, we found new discoveries. This is one of the things why I like IODP: unexpected surprises can be obtained. And also, we can discuss with other expertise people, like physical property specialist and geochemist and reach out various opinions… It’s interesting, to see that. We can also discuss a lot when we look at cores, yes.

BMR: It’s interdisciplinary.

KU: Yes, that’s right.

BMR: Well, thank you very much for your time.

KU: Thank you.

First core on deck! during IODP Expedition 405, where Kohtaro was co-chief scientist. ©️Doriane Letexier / JAMSTEC / IODP.