Ryo Okuwaki

この研究室は、地震と地震以外の現象をターゲットに、それらの震源過程について研究しています。
We study earthquake and non-earthquake source processes.
地震は、地下にある岩石の一部分で急激な破壊すべりが起こり、そのときに地震波が周囲へと放射される現象です。地下深くで起こる破壊現象である地震は、直接目で見たり手に取ったりすることができません。そこで私たちは、数学や物理学、計算科学といったさまざまなアプローチを組み合わせ、この「見えない現象」の解明に取り組んでいます。なかでも、「地震の声」ともいえる地震波形データをはじめとする地球物理学データを手がかりに、地震の震源過程を詳しくイメージングしています。これによって、地震が「いつ・どこで・どのように」起こったのか、巨大地震はなぜそれほど大きく成長してしまうのか、複雑な断層の形は破壊の成長をどのように左右するのか、といった問いに答えることを目指しています。さらに、こうした一瞬の地震発生のしくみが、山脈や断層といった地形・地下構造をつくりながら、長い時間をかけて地球を動かし続けるテクトニクスとどのように結びついているのかにも注目しています。地震をカギとして、地球のダイナミクスを物理的に理解することが大きな目標です。
Earthquake is one of the most energetic Earth dynamics that generates seismic waves by an instantaneous rupture of a rock in Earth. Earthquakes are the "voice" of the Earth, telling us how the tectonic plates move and how the strain energy is stored, so it is critical to get access to earthquake dynamics and its driving mechanism. One of the challenges to study earthquakes is that we cannot directly observe earthquake behaviour, because the earthquake occurs in a deeper part of the Earth. Seismic records should be the primary means to resolve the earthquake behaviours, regardless of the event depth or location. We are developing and applying earthquake-source imaging techniques to unravel earthquake rupture complexities and aiming to answer; how does the earthquake initiate, propagate and terminate?
一方で地震波形データに記録されているのは、地震の震源から放射される莫大なエネルギーだけではありません。人間活動に由来する振動や、火山活動による微動や噴火、さらには大気や海洋の動きに呼応した固体地球のかすかな揺れまでもが、「雑微動」として常に記録され続けています。近年、こうした雑微動のなかに、風変わりな地震波シグナルが潜んでいることがわかり始めてきました。台風や低気圧の発達によって海底下で引き起こされる微小な振動、山間部や海底で発生する地すべり、あるいは大気・海洋の運動と深く結びついた固体地球の変動現象が、その発生源として指摘されています。ただし、これらのシグナルは普通の地震のそれと比べてとても弱く、地震波形データの「ノイズ」に埋もれてしまうため、その正体はまだほとんどわかっていません。この研究室では、そうした「地震以外」のさまざまな振動現象にも目を向けています。海底下や地球の表層で生じる奇妙なシグナルの発生源を見つけ出し、震源過程を解析するアプローチを開発し、その励起メカニズムの解明を目指しています。
Seismic records contain signals from coupled systems of the solid Earth, the ocean, and the atmosphere, which are dominated by non-earthquake signals. However, these signals are complex and difficult to interpret, leaving their excitation sources poorly understood. Often these signals are characterized as noise and rarely examined. We are developing and applying seismic array techniques to explore unconventional seismic sources. We are working on detecting and locating peculiar seismic sources (e.g., icequakes, landslides, volcanic tremors, stormquakes). By analysing unconventional seismic sources, we hope to gain insights of physical mechanisms of those unconventional seismic source processes that are capable of generating spatiotemporally discrete seismic sources but have been missed by conventional catalogs.

members

奥脇亮 / 准教授 / e-mail / CV / Google Scholar

Ryo Okuwaki / Associate professor / e-mail / CV / Google Scholar

青木泰智 / 学生 / 海底活火山周辺における震源検出と震源過程解析

Taichi Aoki / Master's student / Seismicity and source process analyses for submarine volcanoes

田中隼斗 / 学生 / DASを利用した震源過程解析

Hayato Tanaka / Undergraduate student / Seismicity and source process analyses using DAS

兼平菜月 / 学生 / 地震波形データを使った質量移動解析

Hazuki Kanehira / Undergraduate student / Mass transfer analyses using seismological data

publications

Burnett, H. J., Fan, W., Okuwaki, R. & Matsuzawa, T. (submitted). Identifying very low frequency earthquakes in the Japan subduction zone from 2006 to 2016 using the Hi-net high-sensitivity accelerometers. , .
Sato, D. S. K., Yagi, Y., Okuwaki, R., & Fukahata, Y. (submitted). Strike-slip restraining screwed fault geometry reconstructed from the 2025 Myanmar earthquake. , , . 10.31223/X5XX6C
DeSalvio, N. D., Fan, W., & Okuwaki, R. (2026). Seismicity Burst Evolution Suggests Systematic fault zone Condition Changes in Japan after the 2011 M9 Tohoku-oki Earthquake. Journal of Geophysical Research: Solid Earth, 131, . 10.1029/2025JB033202
Sato, D. S. K., Yagi, Y., Okuwaki, R., & Fukahata, Y. (2026). Smooth surface reconstruction of earthquake faults from distributed moment-potency-tensor solutions. Geophysical Journal International, 245, ggag116. 10.1093/gji/ggag116
Yagi, Y., Fukahata, Y., Okuwaki, R., Takagawa, T., & Toda, S. (2025). Breaking the Cycle: Short Recurrence and Overshoot of an M9-class Kamchatka Earthquake. Seismica, 4, 2012. 10.26443/seismica.v4i2.2012
Thingbaijam, K. K. S., Okuwaki, R., & Hobbs, T. E. (2025). Fast Reports of the 2025 Mw 7.8 Mandalay, Myanmar Earthquake: unraveling the rupture characteristics. Seismica, 4, 1914. 10.26443/seismica.v4i2.1914
Hu, WL., Tan, E., Okuwaki, R., & Yagi, Y. (2025). Intraslab stress heterogeneity and continental mantle faulting revealed by the 2006 Pingtung offshore earthquake doublet. Communications Earth & Environment, 6, 726. 10.1038/s43247-025-02719-x
Inoue, N., Yamaguchi, R., Yagi, Y., Okuwaki, R., Enescu, B., & Tadapansawut, T. (2025). A multiple asymmetric bilateral rupture sequence derived from the peculiar tele-seismic P-waves of the 2025 Mandalay, Myanmar earthquake. Seismica, 4, 1691. 10.26443/seismica.v4i1.1691
Yamaguchi, R., Yagi, Y., Okuwaki, R., & Enescu, B. (2025). The complex rupture evolution of the long and slow, tsunamigenic 2021 South Sandwich Islands earthquake. Scientific Reports, 15, 17706. 10.41598/s41598-025-02043-6
Okuwaki, R., Yagi, Y., Murakami, A., & Fukahata, Y. (2024). A Multiplex Rupture Sequence under Complex Fault Network due to Preceding Earthquake Swarms during the 2024 Mw 7.5 Noto Peninsula, Japan, Earthquake. Geophysical Research Letters, 51(11), e2024GL109224. 10.1029/2024GL109224
Ohara, K., Yagi, Y., & Okuwaki, R. (2024). Complex rupture evolution of the 2007 Martinique earthquake: a non-double-couple event in the Caribbean Sea. Geophysical Journal International, 236(3), 1743–1752. 10.1093/gji/ggae024
Yagi, Y., Okuwaki, R., Hirano, S., Enescu, B., Chikamori, M., & Yamaguchi, R. (2024). Barrier-induced rupture front disturbances during the 2023 Morocco earthquake. Seismological Research Letters, 95(3), 1591–1598. 10.1785/0220230357
Ohara, K., Yagi, Y., Yamashita, S., Okuwaki, R., Hirano, S., & Fukahata, Y. (2023). Complex evolution of the 2016 Kaikoura earthquake revealed by teleseismic body waves. Progress in Earth and Planetary Science, 10(35), 1–12. 10.1186/s40645-023-00565-z
Okuwaki, R., Yagi, Y., Taymaz, T., & Hicks, S. P. (2023). Multi-scale rupture growth with alternating directions in a complex fault network during the 2023 south-eastern Türkiye and Syria earthquake doublet. Geophysical Research Letters, 50(12), e2023GL103480. 10.1029/2023GL103480
Yagi, Y., Okuwaki, R., Enescu, B., & Lu, J. (2023). Irregular Rupture Process of the 2022 Taitung, Taiwan, Earthquake Sequence. Scientific Reports, 13, 1107. 10.1038/s41598-023-27384-y
Fang, J., Ou, Q., Wright, T. J., Okuwaki, R., Amey, R. M. J., Craig, T. J., Elliott, J. R., Hooper, A., Lazecky, M., & Maghsoudi, Y. (2022). Earthquake Cycle Deformation Associated with the 2021 Mw 7.4 Maduo (Eastern Tibet) Earthquake: An Intrablock Rupture Event on a Slow-Slipping Fault from Sentinel-1 InSAR and Teleseismic Data. Journal of Geophysical Research: Solid Earth, 127(11), 1–30. 10.1029/2022JB024268
Rowe, C. D., Agius, M., Convers, J., Funning, G., Galasso, C., Hicks, S., Huynh, T., Lange, J., Lecocq, T., Mark, H., Okuwaki, R., Ragon, T., Rychert, C., Teplitzky, S., & van den Ende, M. (2022). The Launch of Seismica: a seismic shift in publishing. Seismica (non-peer reviewed article), 1, 1–14. 10.26443/seismica.v1i1.255
Okuwaki, R. (2022). Chasing supershear earthquakes. Nature Geoscience (non-peer reviewed News & Views article), 15, 863–864. 10.1038/s41561-022-01054-6 | SharedIt link
Yamashita, S., Yagi, Y., Okuwaki, R., Shimizu, K., Agata, R., & Fukahata, Y. (2022). Potency density tensor inversion of complex body waveforms with time-adaptive smoothing constraint. Geophysical Journal International, 231(1), 91–107. 10.1093/gji/ggac181
Tadapansawut, T., Yagi, Y., Okuwaki, R., Yamashita, S., & Shimizu, K. (2022). Complex rupture process on the conjugate fault system of the 2014 Mw 6.2 Thailand earthquake. Progress in Earth and Planetary Science, 9(1), 26. 10.1186/s40645-022-00484-5
Yamashita, S., Yagi, Y., & Okuwaki, R. (2022). Irregular rupture propagation and geometric fault complexities during the 2010 Mw 7.2 El Mayor-Cucapah earthquake. Scientific Reports, 12(1), 4575. 10.1038/s41598-022-08671-6
Fan, W., Barbour, A. J., McGuire, J. J., Huang, Y., Lin, G., Cochran, E. S., & Okuwaki, R. (2022). Very Low Frequency Earthquakes in Between the Seismogenic and Tremor Zones in Cascadia? AGU Advances, 3(2), 1–19. 10.1029/2021AV000607
Fan, W., Okuwaki, R., Barbour, A. J., Huang, Y., Lin, G., & Cochran, E. S. (2022). Fast rupture of the 2009 Mw 6.9 Canal de Ballenas earthquake in the Gulf of California dynamically triggers seismicity in California. Geophysical Journal International, 230(1), 528–541. 10.1093/gji/ggac059
Okuwaki, R., & Fan, W. (2022). Oblique Convergence Causes Both Thrust and Strike-Slip Ruptures During the 2021 M 7.2 Haiti Earthquake. Geophysical Research Letters, 49(2), 1–12. 10.1029/2021GL096373
Okuwaki, R., Hicks, S. P., Craig, T. J., Fan, W., Goes, S., Wright, T. J., & Yagi, Y. (2021). Illuminating a Contorted Slab With a Complex Intraslab Rupture Evolution During the 2021 Mw 7.3 East Cape, New Zealand Earthquake. Geophysical Research Letters, 48(24), 1–13. 10.1029/2021GL095117
Hu, Y., Yagi, Y., Okuwaki, R., & Shimizu, K. (2021). Back-propagating rupture evolution within a curved slab during the 2019 Mw 8.0 Peru intraslab earthquake. Geophysical Journal International, 227(3), 1602–1611. 10.1093/gji/ggab303
Okuwaki, R., Fan, W., Yamada, M., Osawa, H., & Wright, T. J. (2021). Identifying landslides from continuous seismic surface waves: a case study of multiple small-scale landslides triggered by Typhoon Talas, 2011. Geophysical Journal International, 226(2), 729–741. 10.1093/gji/ggab129
Heidarzadeh, M., Pranantyo, I. R., Okuwaki, R., Dogan, G. G., & Yalciner, A. C. (2021). Long Tsunami Oscillations Following the 30 October 2020 Mw 7.0 Aegean Sea Earthquake: Observations and Modelling. Pure and Applied Geophysics, 178(5), 1531–1548. 10.1007/s00024-021-02761-8
Yamashita, S., Yagi, Y., Okuwaki, R., Shimizu, K., Agata, R., & Fukahata, Y. (2021). Consecutive ruptures on a complex conjugate fault system during the 2018 Gulf of Alaska earthquake. Scientific Reports, 11(1), 5979. 10.1038/s41598-021-85522-w
Shimizu, K., Yagi, Y., Okuwaki, R., & Fukahata, Y. (2021). Construction of fault geometry by finite-fault inversion of teleseismic data. Geophysical Journal International, 224(2), 1003–1014. 10.1093/gji/ggaa501
Tadapansawut, T., Okuwaki, R., Yagi, Y., & Yamashita, S. (2021). Rupture Process of the 2020 Caribbean Earthquake Along the Oriente Transform Fault, Involving Supershear Rupture and Geometric Complexity of Fault. Geophysical Research Letters, 48(1), 1–9. 10.1029/2020GL090899
Okuwaki, R., Hirano, S., Yagi, Y., & Shimizu, K. (2020). Inchworm-like source evolution through a geometrically complex fault fueled persistent supershear rupture during the 2018 Palu Indonesia earthquake. Earth and Planetary Science Letters, 547, 116449. 10.1016/j.epsl.2020.116449 | preprint
Hicks, S. P., Okuwaki, R., Steinberg, A., Rychert, C. A., Harmon, N., Abercrombie, R. E., Bogiatzis, P., Schlaphorst, D., Zahradnik, J., Kendall, J.-M., Yagi, Y., Shimizu, K., & Sudhaus, H. (2020). Back-propagating supershear rupture in the 2016 Mw 7.1 Romanche transform fault earthquake. Nature Geoscience, 13(9), 647–653. 10.1038/s41561-020-0619-9 | preprint
Takemura, S., Okuwaki, R., Kubota, T., Shiomi, K., Kimura, T., & Noda, A. (2020). Centroid moment tensor inversions of offshore earthquakes using a three-dimensional velocity structure model: slip distributions on the plate boundary along the Nankai Trough. Geophysical Journal International, 222(2), 1109–1125. 10.1093/gji/ggaa238
Aránguiz, R., Esteban, M., Takagi, H., Mikami, T., Takabatake, T., Gómez, M., González, J., Shibayama, T., Okuwaki, R., Yagi, Y., Shimizu, K., Achiari, H., Stolle, J., Robertson, I., Ohira, K., Nakamura, R., Nishida, Y., Krautwald, C., Goseberg, N., & Nistor, I. (2020). The 2018 Sulawesi tsunami in Palu city as a result of several landslides and coseismic tsunamis. Coastal Engineering Journal, 62(4), 445–459. 10.1080/21664250.2020.1780719
Shimizu, K., Yagi, Y., Okuwaki, R., & Fukahata, Y. (2020). Development of an inversion method to extract information on fault geometry from teleseismic data. Geophysical Journal International, 220(2), 1055–1065. 10.1093/gji/ggz496
Hirano, S., & Okuwaki, R. (2020). Note on "Backprojection to image slip". OSF non-peer reviewed preprint. 10.17605/osf.io/pb7hk
Okuwaki, R., Kasahara, A., Yagi, Y., Hirano, S., & Fukahata, Y. (2019). Backprojection to image slip. Geophysical Journal International, 216(3), 1529–1537. 10.1093/gji/ggy505
Aránguiz, R., Urra, L., Okuwaki, R., & Yagi, Y. (2018). Development and application of a tsunami fragility curve of the 2015 tsunami in Coquimbo, Chile. Natural Hazards and Earth System Sciences, 18(8), 2143–2160. 10.5194/nhess-18-2143-2018
Okuwaki, R., & Yagi, Y. (2018). Role of geometric barriers in irregular-rupture evolution during the 2008 Wenchuan earthquake. Geophysical Journal International, 212(3), 1657–1664. 10.1093/gji/ggx502
Okuwaki, R., & Yagi, Y. (2017). Rupture Process During the Mw 8.1 2017 Chiapas Mexico Earthquake: Shallow Intraplate Normal Faulting by Slab Bending. Geophysical Research Letters, 44(23), 11,816-11,823. 10.1002/2017GL075956
Miyakawa, A., Sumita, T., Okubo, Y., Okuwaki, R., Otsubo, M., Uesawa, S., & Yagi, Y. (2016). Volcanic magma reservoir imaged as a low-density body beneath Aso volcano that terminated the 2016 Kumamoto earthquake rupture. Earth, Planets and Space, 68(1), 208. 10.1186/s40623-016-0582-2
Yagi, Y., Okuwaki, R., Enescu, B., Kasahara, A., Miyakawa, A., & Otsubo, M. (2016). Rupture process of the 2016 Kumamoto earthquake in relation to the thermal structure around Aso volcano. Earth, Planets and Space, 68(1), 118. 10.1186/s40623-016-0492-3
Okuwaki, R., Yagi, Y., Aránguiz, R., González, J., & González, G. (2016). Rupture Process During the 2015 Illapel, Chile Earthquake: Zigzag-Along-Dip Rupture Episodes. Pure and Applied Geophysics, 173(4), 1011–1020. 10.1007/s00024-016-1271-6
Mai, P. M., Schorlemmer, D., Page, M., Ampuero, J., Asano, K., Causse, M., Custodio, S., Fan, W., Festa, G., Galis, M., Gallovic, F., Imperatori, W., Käser, M., Malytskyy, D., Okuwaki, R., Pollitz, F., Passone, L., Razafindrakoto, H. N. T., Sekiguchi, H., Song, S. G., Somala, S. N., Thingbaijam, K. K. S., Twardzik, C., van Driel, M., Vyas, J. C., Wang, R., Yagi, Y., & Zielke, O. (2016). The Earthquake-Source Inversion Validation (SIV) Project. Seismological Research Letters, 87(3), 690–708. 10.1785/0220150231
Aránguiz, R., González, G., González, J., Catalán, P. A., Cienfuegos, R., Yagi, Y., Okuwaki, R., Urra, L., Contreras, K., Del Rio, I., & Rojas, C. (2016). The 16 September 2015 Chile Tsunami from the Post-Tsunami Survey and Numerical Modeling Perspectives. Pure and Applied Geophysics, 173(2), 333–348. 10.1007/s00024-015-1225-4
Yagi, Y., & Okuwaki, R. (2015). Integrated seismic source model of the 2015 Gorkha, Nepal, earthquake. Geophysical Research Letters, 42(15), 6229–6235. 10.1002/2015GL064995
Yagi, Y., Okuwaki, R., Enescu, B., & Fukahata, Y. (2015). Unusual low-angle normal fault earthquakes after the 2011 Tohoku-oki megathrust earthquake. Earth, Planets and Space, 67(1), 100. 10.1186/s40623-015-0271-6
Okuwaki, R., Yagi, Y., & Hirano, S. (2014). Relationship between High-frequency Radiation and Asperity Ruptures, Revealed by Hybrid Back-projection with a Non-planar Fault Model. Scientific Reports, 4(1), 7120. 10.1038/srep07120
Yagi, Y., Okuwaki, R., Enescu, B., Hirano, S., Yamagami, Y., Endo, S., & Komoro, T. (2014). Rupture process of the 2014 Iquique Chile Earthquake in relation with the foreshock activity. Geophysical Research Letters, 41(12), 4201–4206. 10.1002/2014GL060274