We asked the two students who were selected for FY2025 Integrated Research Project about various aspects of the project. Please take a look!
【Researcher Name】
Kensuke Shobusako (Graduate School of Science, Department of Earth and Planetary Sciences)
Shujiro Fujioka (Graduate School of Engineering, Department of Civil Engineering)
【Integrated Research Title】
The Mesh-Free Method: Pioneering a Borderless Next-Generation Earthquake and Tsunami Simulator for Geophysics and Disaster Prevention Engineering
【Research Abstract】
Predicting earthquakes and tsunamis in Japan is an urgent societal challenge. However, conventional earthquake prediction relies on earthquake cycles based on past observational data, limiting its ability to forecast unprecedented megathrust earthquakes and tsunamis. Earthquakes accompanied by tsunamis originate from subduction of oceanic plates, yet computational methods treating this as part of mantle convection remain unestablished. This research aims to construct a pioneering computational method for earthquake and tsunami prediction by reproducing oceanic plate subduction phenomena using the mesh-free method (particle method).
Q1. What prompted you to start this joint research?
What prompted this joint research was the fact that we shared a common foundational technology, the Smoothed Particle Hydrodynamics (SPH) method, despite belonging to different fields. As it turns out, we both coincidentally belong to the same club (the Kyushu University Men’s Choir, Chor Akademie), which gave us the fortunate opportunity to discuss each other’s research. I (Shobuzako) was studying the phenomenon of Earth’s mantle convection from a planetary science perspective, while Fujioka was studying natural disaster phenomena from a disaster prevention engineering perspective, both using the SPH method. Although our fields are completely different, as we learned more about each other’s work, we came to believe that by applying this common computational method, we can tackle a greater challenge than either of us can alone. Therefore, as the first project to fuse our expertise, we decided to launch a simulation study of the magnificent phenomenon of oceanic plate subduction.
Q2. How did you feel about being selected for the Integrated Research Project?
(Shobuzako) I am deeply honored that our research project was selected and recognized for its great potential. At the same time, receiving this research funding has renewed my determination to tackle the challenging theme of interdisciplinary research responsibly and to ensure that we produce significant results.
(Fujioka) I am deeply honored to have been selected for this project. I regard it as a unique and invaluable opportunity
of the SPRING to create new value through interdisciplinary collaboration. I am determined to make the most of this opportunity and devote myself wholeheartedly to my research.
Q3. What is the current progress of your joint research?
The overall project is about 50 % complete. We are currently working on adapting our new, jointly developed high-accuracy method, the Least Squares SPH (LS-SPH) method, for application to complex phenomena with free surfaces, such as tsunamis. Once this phase is complete, we can finally begin to tackle the main goal of our project: the simulation of oceanic plate subduction.
Q4. What new “insights” have you gained while conducting joint research?
(Shobuzako) Since the SPH method is a mesh-free method, I had always thought it was completely different from conventional methods that use a fixed spatial grid, such as the finite difference method or the finite element method. However, as we delved deeper into the theory through discussions with Fujioka, we made a fundamental discovery; : the two approaches are, in fact, very closely related mathematically. I feel this realization was a major step forward, as it opens the way to applying insights from conventional methods to the SPH framework.
(Fujioka) I have so far focused my research on improving the accuracy of the SPH method. However, through collaborative work with Mr. Shobuzako from the Graduate School of Science, I realized that I had not fully understood the mathematical foundations underlying high-accuracy SPH methods. Furthermore, through this collaboration, I deepened my mathematical understanding, which enabled me to discover new possibilities for applying the SPH method —a significant learning experience for me.
Q5. What are some of the difficulties of joint research that you did not think of when you were planning (applying for) this project?
A significant challenge we encountered is the inherent trade-off between computational accuracy and numerical stability. We found that attempts to enhance the precision of our calculations often introduced instabilities, while prioritizing stability invariably meant compromising accuracy. At the proposal stage, we had not fully appreciated the difficulty of reconciling these two competing objectives. Through our daily process of trial and error, we have gained a profound appreciation for the rigorous nature of research, where progress is often non-linear and feels like taking one step forward, only to take half a step back.
Q6. What is the reaction of your academic advisors and the members around you in the lab?
(Shobuzako) We have been receiving strong support from our respective academic supervisors. My advisor, Associate Professor Shigeo Yoshida, consistently offers advice from the perspective of geophysics, while Fujioka’s advisor, Professor Mitsuteru Asai, provides guidance from the viewpoint of computational engineering. In fact, I had been participating in Professor Asai’s lab seminars even before this project was selected, and this forum for cross-disciplinary discussion laid the foundation for our collaboration. Furthermore, we regularly exchange ideas about the particle method with the students in both labs, which has created a very fortunate and supportive environment for our research.
(Fujioka) I had already been engaged in discussions on the SPH method with Mr. Shobuzako before the adoption of this project, as he had been participating in seminars in my laboratory. Since the adoption, we have been bringing together perspectives from geophysics and disaster prevention engineering and have been conducting discussions with an emphasis on interdisciplinary integration. Whenever gaps arise, our supervisors provide us with appropriate advice, which has been a highly reassuring source of support. In addition, many members of my laboratory are considering pursuing further studies, and by learning about the existence of this project, the number of those who wish to take on such a challenge when given the opportunity has increased, bringing positive stimulation to the entire group
Q7. How do you actually conduct this joint research? (online, get together in a lab, etc.)
We have a research meeting once a week, and we use tools like Slack for day-to-day communication and sharing our calculation results. We work on the theoretical aspects of the project together, while the implementation is divided according to our respective areas of expertise. This approach allows us to conduct our research efficiently.
Q8. How did you spend your research budget? What could you do/what would you like to do if you had another research budget?
We are carefully using the research funds we received to cover open-access publication fees for our academic papers and travel expenses for domestic conferences, which helps us share our research findings widely with the global community. If we had an additional budget, we would like to purchase a high-performance computer to enable us to run larger-scale simulations.
Q9. Do you think there is a good chance of presenting this joint research at a conference or writing a paper? What percentage do you think there is?
We have an achievement rate of 100%. Through our joint research, we developed a generalized model of the SPH method called the “Least Squares SPH (LS-SPH) method,” which can achieve any accuracy. Our paper on this work has already been published in the journal Results in Applied Mathematics. We also presented these findings at a conference of the Japan Society for Computational Engineering and Science.
Publication details:
Kensuke Shobuzako, Shigeo Yoshida, Yoshifumi Kawada, Ryosuke Nakashima, Shujiro Fujioka, & Mitsuteru Asai (2025) A generalized smoothed particle hydrodynamics method based on the moving least squares method and its discretization error estimation, Results in Applied Mathematics, Volume 26, 100594.
https://doi.org/10.1016/j.rinam.2025.100594
Q10. What are your future prospects and aspirations for this joint research?
The subduction of oceanic plates, which we are studying in this project, is the very mechanism that causes massive earthquakes. Successfully simulating this will be a major milestone toward our ultimate goal of completing an earthquake and tsunami simulator using the SPH method. This joint project is the first step toward that grand objective, and we intend to continue to deepen our collaboration in the future.
Q11. What are your dreams for the future and what kind of person do you both aspire to be?
(Shobuzako) My goal is to become a researcher who is not confined to a single specialty, but who can understand and explain a wide range of natural phenomena using the universal languages of physics and mathematics. With the powerful computational fluid dynamics tool of the SPH method, I would like to continue tackling the mysteries of everything from the dynamics of the Earth’s interior to everyday fluid phenomena, transcending the boundaries of different fields. Ultimately, I hope that my research findings will contribute to solving societal challenges.
(Fujioka) I aim to become a researcher who can contribute to disaster prevention and mitigation by achieving outcomes that minimize the number of disaster victims as much as possible and return those achievements to society. While my research has primarily focused on the SPH method, through collaborative work, I have realized that insights from other methods can also be applied to its mathematical aspects. Moving forward, I aspire to become a researcher equipped with multifaceted abilities, capable of flexibly employing multiple approaches to achieve this goal.
Q12. Please leave a message for the program students who follow to take on the challenge of the Integrated Research Project and joint research.
(Shobuzako) When you feel stuck doing research in your own specialized field alone, a perspective from a different field can sometimes create an unexpected breakthrough. I myself have experienced that many times through this joint research. If you find a topic or a person that you feel is even a little interesting, please try to start by simply having a casual conversation. From there, I am sure that a door to new research will open. I really hope that you will take on the challenge of this valuable opportunity.
(Fujioka) In collaborative research, you can encounter perspectives and approaches that you might not notice on your own. In my own experience, by learning mathematical ways of thinking from other fields, I was able to discover new possibilities for the SPH method. You may feel uncertain at first, but by engaging in discussions with people from different areas of expertise, you will surely gain discoveries and learning opportunities. Through the Emergent Subjects program, I believe you can easily reach out to others, so I encourage you to give it a try.
