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• 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、地下の岩石のいち部分に急激な破壊すべりが起こり、地震波を放射する現象です。地下深くで発生する破壊現象としての地震は、直接目で観察したり、手にとったりすることができません。 そこで、数学・物理学、計算科学など、様々なアプローチを駆使しながら、この見えない現象の解明に取り組んでいます。 とくに、「地震の声」ともいえる地震波形データなど、地球物理学データを使って地震の震源過程を詳細にイメージングすることで、 破壊現象としての地震が、いつ・どこで・どのように発生したのか、巨大地震はなぜ巨大に成長してしまったのか、複雑な断層形状は地震破壊の成長をどのようにコントロールするのか、を解明することを目標に研究をしています。 また、こうした瞬間的な地震発生機構が、山岳や断層構造の形成に関わる、長い期間にわたって地球を駆動するテクトニクスとどのように関係するのかに着目し、地震の発生をカギに、地球のダイナミックな動きを物理的に理解することを目指します。
• 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は、地震時に震源から放射される莫大なエネルギーだけでなく、地震以外の、例えば人間活動に由来する振動現象や、火山活動に起因する微動などに加えて、大気・海洋の摂動に呼応した固体地球の揺れが雑微動として常時記録されています。 雑微動には、台風・低気圧の発達により海底下で誘発される微小な振動現象や、山間部や海底で発生する地すべり、大気・海洋の運動と密接に関連した固体地球変動現象に励起される奇妙な地震波シグナルの存在が指摘され始めています。 一方、そうしたシグナルは、普通の地震シグナルと比較するとたいへん微弱であり、地震波形データの「ノイズ」として埋もれてしまい、その実態はほとんど不明です。 この研究室では、「地震以外」のさまざまな振動現象にも着目し、地震波形データを用いて、海底下や地球表層で生じる奇妙なシグナル励起源の新たな検出法の開発を行い、日本や世界で観測される連続地震波形データに適用し、その励起メカニズムを明らかにすることを目標に研究をしています。
• 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.
• 研究キーワード：
  固体地球物理学、地震学、環境地震学、地震発生物理学、震源過程イメージング (バックプロジェクション、震源インバージョン)、地震波形データ解析、雑微動、 大気・海洋・固体地球連関、地震計アレイ解析、地すべり、火山活動
• Keywords:
  Geophysics, Seismology, Earthquake seismology, Earthquake-source kinematics and physics, Earthquake source imaging (backprojection, finite-fault modeling), Earth’s subsurface phenomena, Environmental seismology, Array seismology

* 一部のゼミは八木勇治教授の研究室と共同で実施しています。

* also co-advising students at Prof. Yujj Yagi's laboratory

• DeSalvio, N. D., Fan, W., & Okuwaki, R. (submitted). Seismicity burst evolution suggests systematic fault-zone condition changes in Japan after the 2011 M9 Tohoku-oki earthquake. , , .
• Yagi, Y., Fukahata, Y., Okuwaki, R., Takagawa, T., & Toda, S. (submitted). Breaking the Cycle: Short Recurrence and Overshoot of an M9-class Kamchatka Earthquake. , , . 10.31223/X5475Z
• 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
• Sato, D. S. K., Yagi, Y., Okuwaki, R., & Fukahata, Y. (submitted). Smooth surface reconstruction of earthquake faults from distributed potency beachballs. , , . 10.48550/arXiv.2506.14082
• 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, 1–2. 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